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          WEBDAV Working Group                     Y. Y. Goland, Microsoft
          INTERNET-DRAFT                 E. J. Whitehead, Jr., U.C. Irvine
          <draft-ietf-webdav-protocol-04>               A. Faizi, Netscape
                                                       S. R Carter, Novell
                                                         D. Jensen, Novell
          Expires April 20, 1998                          October 12, 1997
          
          
                   Extensions for Distributed Authoring and Versioning
                                        on the
                                World Wide Web -- WEBDAV
          
          
          Status of this Memo
          
          This document is an Internet-Draft. Internet-Drafts are working
          documents of the Internet Engineering Task Force (IETF), its
          areas, and its working groups. Note that other groups may also
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          Internet-Drafts are draft documents valid for a maximum of six
          months and may be updated, replaced, or made obsolete by other
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          Distribution of this document is unlimited. Please send comments
          to the Distributed Authoring and Versioning (WEBDAV) working
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          Discussions of the WEBDAV working group are archived at
          <URL:http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth>.
          
          
          Abstract
          
          This Document specifies a set of methods and content-types
          ancillary to HTTP/1.1 for the management of resource properties,
          simple name space manipulation, simple resource locking
          (collision avoidance) and resource version control.
          
          
                                  Table of Contents
          Abstract
          1    Terminology
          2    Data Model and Methods for DAV Properties
               2.1  Introduction
                    2.1.1   The DAV Property
                    2.1.2   Existing Metadata Proposals
                    2.1.3   Properties and HTTP Headers
               2.2  A Property Model for HTTP Resources
                    2.2.1   Overview
                    2.2.2   Property Namespace
               2.3  Schemas
                    2.3.1   PropSchema XML Element
                    2.3.2   DTD XML Element
                    2.3.3   DefinedProps XML Element
          
          
          
          
          
          
                    2.3.4   PropEntries XML Element
                    2.3.5   Live XML Element
               2.4  DAV Schema
                    2.4.1   DAV Property
                    2.4.2   Level XML Element
                    2.4.3   Prop XML element
                    2.4.4   PropLoc XML Attribute
                    2.4.5   Example
               2.5  Property Identifiers
                    2.5.1   Problem Definition
               2.6  Link XML Element
                    2.6.1   Problem Description
                    2.6.2   Solution Requirements
                    2.6.3   Link XML Element
                    2.6.4   Src XML Element
                    2.6.5   Dst XML Element
                    2.6.6   Example
               2.7  Multi-Status Response
                    2.7.1   Problem Definition
                    2.7.2   Solution Requirements
                    2.7.3   Multi-Status Response
               2.8  Properties and Methods
                    2.8.1   DELETE
                    2.8.2   GET
                    2.8.3   PROPPATCH
                    2.8.4   PUT
                    2.8.5   PROPFIND
          3    A Proposal for Collections of Web Resources and Name Space
               Operations
               3.1  Observations on the HTTP Object Model
                    3.1.1   Collection Resources
                    3.1.2   Creation and Retrieval of Collection
                            Resources
                    3.1.3   Source Resources and Output Resources
               3.2  MKCOL Method
                    3.2.1   Problem Description
                    3.2.2   Solution Requirements
                    3.2.3   Request
                    3.2.4   Response
                    3.2.5   Example
               3.3  Standard DAV Properties
                    3.3.1   IsCollection Property
                    3.3.2   DisplayName Property
                    3.3.3   CreationDate Property
                    3.3.4   GETentity Property
                    3.3.5   INDEXentity Property
                    3.3.6   Content-Type XML Element
                    3.3.7   Content-Length XML Element
                    3.3.8   Content-Language XML Element
                    3.3.9   Last-Modified XML Element
                    3.3.10  Etag XML Element
               3.4  INDEX Method
                    3.4.1   Problem Description
                    3.4.2   Solution Requirements
                    3.4.3   The Request
                    3.4.4   The Response
                    3.4.5   ResInfo XML Element
                    3.4.6   Members XML Element
                    3.4.7   Href XML Element
                    3.4.8   Example
               3.5  Behavior of RFC 2068 Methods on Collections
                    3.5.1   GET, HEAD for Collections
                    3.5.2   POST for Collections
                    3.5.3   PUT for Collections
                    3.5.4   DELETE for Collections
          
          
          
          
          
          
                    3.5.5   DELETE Method for Non-Collection
                            Resources
               3.6  COPY Method
                    3.6.1   Problem Description
                    3.6.2   Solution Requirements
                    3.6.3   The Request
                    3.6.4   The Response
                    3.6.5   Examples
               3.7  MOVE Method
                    3.7.1   Problem Description
                    3.7.2   Solution Requirements
                    3.7.3   The Request
                    3.7.4   The Response
                    3.7.5   Examples
               3.8  ADDREF Method
                    3.8.1   Problem Definition
                    3.8.2   Solution Requirements
                    3.8.3   The Request
                    3.8.4   Example
               3.9  DELREF Method
                    3.9.1   Problem Definition
                    3.9.2   Solution Requirements
                    3.9.3   The Request
                    3.9.4   Example
               3.10 PATCH Method
                    3.10.1  Problem Definition
                    3.10.2  Solution Requirements
                    3.10.3  The Request
                    3.10.4  text/xml elements for PATCH
                    3.10.5  The Response
                    3.10.6  Examples
               3.11 Headers
                    3.11.1  Destination Header
                    3.11.2  Enforce-Live-Properties Header
                    3.11.3  Overwrite Header
                    3.11.4  Destroy Header
                    3.11.5  Collection-Member Header
               3.12 Links
                    3.12.1  Source Link Property Type
          4    State Tokens
               4.1  Overview
                    4.1.1   Problem Description
                    4.1.2   Solution Requirements
               4.2  State Token Syntax
               4.3  State Token Conditional Headers
                    4.3.1   If-State-Match
                    4.3.2   If-None-State-Match
               4.4  State Token Header
               4.5  E-Tag
          5    Locking
               5.1  Locking: Introduction
                    5.1.1   Exclusive Vs. Shared Locks
                    5.1.2   Required Support
               5.2  LOCK Method
                    5.2.1   Operation
                    5.2.2   The Effect of Locks on Properties and
                            Containers
                    5.2.3   Locking Replicated Resources
                    5.2.4   Locking Multiple Resources
                    5.2.5   Interaction with other Methods
                    5.2.6   Lock Compatibility Table
                    5.2.7   Status Codes
                    5.2.8   Lock-Info Request Header
                    5.2.9   Owner Request Header
                    5.2.10  Time-Out Header
                    5.2.11  Lock Response
          
          
          
          
          
          
                    5.2.12  Example - Simple Lock Request
                    5.2.13  Example - Multi-Resource Lock Request
               5.3  Write Lock
                    5.3.1   Methods Restricted by Write Locks
                    5.3.2   Write Locks and Properties
                    5.3.3   Write Locks and Null Resources
                    5.3.4   Write Locks and Collections
                    5.3.5   Write Locks and COPY/MOVE
                    5.3.6   Re-issuing Write Locks
                    5.3.7   Write Locks and The State-Token Header
               5.4  Lock Tokens
                    5.4.1   Problem Description
                    5.4.2   Lock Token Introduction
                    5.4.3   Generic Lock Tokens
                    5.4.4   OpaqueLockToken Lock Token
               5.5  UNLOCK Method
                    5.5.1   Problem Definition
                    5.5.2   Example
               5.6  Discovery Mechanisms
                    5.6.1   Lock Capability Discovery
                    5.6.2   Active Lock Discovery
          6    Version Control
          7    Internationalization Support
          8    Security Considerations
          9    Copyright
          10   Acknowledgements
          11   References
          12   Authors' Addresses
          
          
          
          1    Terminology
          
          Collection - A resource that contains member resources.
          
          Member Resource - a resource referred to by a collection. There
          are two types of member resources: external and internal.
          
          Internal Member Resource - the name given to a member resource of
          a collection whose URI is relative to the URI of the collection.
          
          External Member Resource - a member resource with an absolute URI
          that is not relative to its parent’s URI.
          
          Properties - A set of name/value pairs that contain descriptive
          information about a resource.
          
          Live Properties - Properties whose semantics and syntax are
          enforced by the server. For example, a live "read-only" property
          that is enforced by the server would disallow PUTs to the
          associated resource.
          
          Dead properties - Properties whose semantics and syntax are not
          enforced by the server. A dead "read-only" property would not be
          enforced by the server and thus would not be used by the server
          as a reason to disallow a PUT on the associated resource.
          
          The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
          NOT", "SHOULD", SHOULD NOT", "RECOMMENDED",  "MAY", and
          "OPTIONAL" in this document are to be interpreted as described in
          RFC 2119 [Bradner, 1997].
          
          
          2    Data Model and Methods for DAV Properties
          
          
          
          
          
          
          2.1  Introduction
          
          
          2.1.1     The DAV Property
          
          Properties are pieces of data that describe the state of a
          resource. Properties are data about data. The term property is
          used within this specification to disambiguate the concept from
          the overloaded terms "metadata" and "attribute".
          
          Properties are used within distributed authoring environments to
          provide for efficient discovery and management of resources. For
          example, a 'subject' property might allow for the indexing of all
          resources by their subject, and an 'author' property might allow
          for the discovery of what authors have written which documents.
          
          
          2.1.2     Existing Metadata Proposals
          
          Properties have a long played an essential role in the
          maintenance of large document repositories, and many current
          proposals contain some notion of a property. These include PICS
          [Miller et al., 1996], PICS-NG, the Rel/Rev draft [Maloney,
          1996], Web Collections, XML [Bray, Sperberg-McQueen, 1997],
          several proposals on representing relationships within HTML,
          digital signature manifests (DCMF), and a position paper on Web
          metadata architecture [Berners-Lee, 1997].
          
          Some proposals come from a digital library perspective. These
          include the Dublin Core [Weibel et al., 1995] metadata set and
          the Warwick Framework [Lagoze, 1996], a container architecture
          for different metadata schemas. The literature includes many
          examples of metadata, including MARC [MARC, 1994], a
          bibliographic metadata format, RFC 1807 [Lasher, Cohen, 1995], a
          technical report bibliographic format employed by the Dienst
          system, and the proceedings from the first IEEE Metadata
          conference describe many community-specific metadata sets.
          
          Participants of the 1996 Metadata II Workshop in Warwick, UK
          [Lagoze, 1996], noted that, "new metadata sets will develop as
          the networked infrastructure matures" and "different communities
          will propose, design, and be responsible for different types of
          metadata." These observations can be corroborated by noting that
          many community-specific sets of metadata already exist, and there
          is significant motivation for the development of new forms of
          metadata as many communities increasingly make their data
          available in digital form, requiring a metadata format to assist
          data location and cataloging.
          
          
          2.1.3     Properties and HTTP Headers
          
          Properties already exist, in a limited sense, within HTTP through
          the use of message headers. However, in distributed authoring
          environments a relatively large number of properties are needed
          to describe the state of a resource, and setting/returning them
          all through HTTP headers is inefficient. Thus a mechanism is
          needed which allows a principal to identify a set of properties
          in which the principal is interested and to then set or retrieve
          just those properties.
          
          
          2.2  A Property Model for HTTP Resources
          
          
          
          
          
          
          2.2.1     Overview
          
          The DAV property model is based on name/value doubles. The name
          of a property identifies the property's syntax and semantics, and
          provides an address with which to refer to a property. The name
          and value of a property is expressed as a well-formed XML
          element, where the name of the property is the name of the XML
          element, and the value of the property MUST be either blank, or a
          well-formed XML element value.
          
          
          2.2.2     Property Namespace
          
          
          2.2.2.1   Problem Definition
          
          The requirement is to be able to associate a value with a
          property name on a resource.  It must be possible to associate a
          URL with the property name.
          
          
          2.2.2.2   Solution Requirement
          
          Ideally a property namespace should work well with extant
          property implementations as well as database systems. The DAV
          property namespace has been specified with the following two
          facts in mind:
          ·    Namespaces associated with flat file systems are ubiquitous.
          ·    The majority of databases use a fixed schema mechanism.
          The last point makes efficient implementation of hierarchical
          properties difficult. Specifically, each property has a random
          set of children; the best a relational database can do is provide
          a table with name and value, where the value is a series of
          indexes into other tables and each index represents a specific
          value. However most RDBS do not provide for table pointers, only
          index values. Such a system would have to be jury-rigged to
          handle table pointers. In addition, indexing systems are
          optimized for a small set of relatively large tables;
          hierarchical property systems tend toward many properties, each
          with different numbers and types of children, thus potentially
          requiring a table for each child.
          
          It would seem best to implement a flat property namespace,
          inducing a natural isomorphism between DAV and most native file
          systems. Adopting such a model will not restrict RDBS from taking
          full advantage of their search facilities.
          
          However, it seems that future trends might be toward hierarchical
          properties. Therefore, DAV requirements [Slein et al.] stipulate
          that the design of the flat property system MUST be such that it
          will be possible to add true hierarchical properties later
          without breaking downlevel clients. Specifically, a flat client
          MUST be able to speak to a hierarchical server and a hierarchical
          client MUST be able to speak to a flat server. Worst case either
          way MUST be that the request fails.
          
          
          2.2.2.3   Property Names
          
          A property name identifies both the syntax and semantics of the
          property's value. It is critical that property names do not
          collide, e.g., two principals defining the same property name
          with two different meanings.
          
          The URI framework provides a mechanism to prevent namespace
          
          
          
          
          
          
          collision and for varying degrees of administrative control.
          Rather than reinvent these desirable features, DAV properties
          make use of them by requiring that all DAV property names MUST be
          URIs.  Since a property is also an XML element, the name of the
          XML element is a URI.
          
          The property namespace is flat, that is, it is not possible to
          string together a series of property names in order to refer to a
          hierarchy of properties. Thus it is possible to refer to a
          property B but not a property A/B, where A is also a property
          defined on the resource.
          
          Finally, it is not possible to define the same property twice as
          this would cause a collision in the resource's property
          namespace.
          
          
          2.3  Schemas
          
          A schema is a group of property names and XML elements.
          
          Schema discovery is used to determine if a system supports a
          group of properties or XML elements. A property does not
          necessarily contain sufficient information to identify any
          schema(s) to which it may belong.
          
          As with property names, schemas MUST use URIs as their names.
          
          A resource declares its support for a schema by defining a
          property whose name is the same as the schema's. The property
          SHOULD contain the PropSchema XML element.
          
          
          2.3.1     PropSchema XML Element
          
          Name:     http://www.ietf.org/standards/dav/PropSchema
          Purpose:  To provide information about properties
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   [DTD] [DefinedProps]
          Description:This property contains the definition of the schema.
          This definition consists of two parts. A DTD element that
          contains a DTD that declares all XML elements and DefinedProps
          that defines any properties associated with the schema. As with
          all XML it is possible to add extra XML elements. Therefore
          schemas may define extra XML elements which are to be included
          with their values.
          
          2.3.2     DTD XML Element
          
          Name:          http://www.ietf.org/standards/dav/DTD
          Purpose:  To contain the DTD for XML elements associated with the
          schema.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values:   XML Declaration statements
          
          
          2.3.3     DefinedProps XML Element
          
          Name:          http://www.ietf.org/standards/dav/DefinedProps
          Purpose:  To contain a list of properties defined by the schema.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   1*PropEntries
          
          
          
          
          
          
          
          
          2.3.4     PropEntries XML Element
          
          Name:          http://www.ietf.org/standards/dav/PropEntries
          Purpose:  To contain the name of a defined property, the DTD of
          its value, and its live/dead status.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   DefinedProps
          Values=   Prop [DTD] [Live]
          Description:Prop contains the name of the property. The DTD
          contains the DTD of the property's value. Live, if defined,
          indicates that the property has semantics and syntax that are
          enforced by the server.
          
          
          2.3.5     Live XML Element
          
          Name:          http://www.ietf.org/standards/dav/Live
          Purpose:  If present this indicates the server MUST enforce the
          syntax and semantics of the property.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   PropEntries
          
          
          2.4  DAV Schema
          
          The DAV Schema is specified as
          http://www.ietf.org/standards/dav/. This schema is used to
          indicate support for
          ·    properties that may be defined on a resource and
          ·    XML elements that may be returned in responses.
          
          
          2.4.1     DAV Property
          
          Name:          http://www.ietf.org/standards/dav
          Purpose:  Defines support for the DAV schema and protocol.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   PropSchema Level
          Description:This property indicates that the resource supports
          the DAV schema and protocol to the level indicated. THE VALUE IN
          PROPSCHEMA IS TBD, WE NEED TO PROVIDE IT IN AN APPENDIX.
          
          
          2.4.2     Level XML Element
          
          Name:          http://www.ietf.org/standards/dav/level
          Purpose:  To indicate the level of DAV compliance the resource
          meets.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   DAV
          Values=   "1" | "2" | "3"
          Description:A value of 1 for level indicates that the resource
          supports the property and namespace sections of the DAV
          specification. Level 2 indicates that the resource supports level
          1 and the lock section of the specification, with a minimum
          locking capability of the write lock. Level 3 indicates support
          for levels 1 and 2 as well as support for the versioning section
          of the DAV specification.
          
          
          2.4.3     Prop XML element
          
          Name:          http://www.ietf.org/standards/dav/prop
          
          
          
          
          
          
          Purpose:  Contains properties related to a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values:   XML Elements
          Description:The Prop XML element is a generic container for
          properties defined on resources. All elements inside Prop MUST
          define properties related to the resource. No other elements may
          be used inside of a Prop element.
          
          
          2.4.4     PropLoc XML Attribute
          
          Name:          http://www.ietf.org/standards/dav/PropLoc
          Purpose:  To specify the location of the associated property.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   URL
          Description:This attribute is used with elements inside of Props
          contained in responses to specify the URL of the property on the
          associated resource. The PropLoc attribute MUST NOT be used in
          requests.
          
          
          2.4.5     Example
          
          <?XML:Namespace href="http://www.ietf.org/standards/dav/"
          AS="D"/>
          <?XML:Namespace href="AIIM:Dublin:" AS="A"/>
          <D:Prop>
               <A:Author
          D:PropLoc="http://www.foo.com/resource/props/Author">
                    Larry Masinter
               </A:Author>
          </D:Prop>
          
          The previous specifies that the property author exists on some
          unspecified resource and that the property can be directly
          referenced at http://www.foo.com/resource/props/Author. The
          resource upon which the property is defined must be determined
          from context.
          
          
          2.5  Property Identifiers
          
          
          2.5.1     Problem Definition
          
          DAV properties are resources and thus may have a URI where the
          value of an instance of the property may be retrieved.  This URI
          is separate from the URI name of the property, which identifies
          the syntax and semantics of the property, but which does not give
          information on how to access the value of an instance of the
          property.
          
          A server is free to assign whatever URI it chooses to identify an
          instance of a property defined on a resource. In fact, a server
          is free not to reveal the URI of an instance of a particular
          resource and instead require that the client access the property
          through PROPFIND and PROPPATCH.  However, many servers will want
          to allow clients to directly manipulate properties. On these
          servers, a client can discover the URI of an instance of a
          property by performing a PROPFIND and examining the PropLoc
          attribute, if returned, of each property.
          
          2.6  Link XML Element
          
          
          
          
          
          
          
          2.6.1     Problem Description
          
          A mechanism is needed to associate resources with other
          resources. These associations, known as links, consist of three
          values, a type describing the nature of the association, the
          source of the link, and the destination of the link. In the case
          of annotation, neither the source nor the destination of a link
          need be the resource upon which the link is recorded.
          
          
          2.6.2     Solution Requirements
          
          The association mechanism MUST make use of the DAV property
          mechanism in order to make the existence of the associations
          searchable.
          
          
          2.6.3     Link XML Element
          
          Name:          http://www.ietf.org/standards/dav/link
          Purpose:  To identify a property as a link and to contain the
          source and destination of that link.
          Schema:   http://www.ietf.org/standards/dav/
          Values=   1*Src 1*Dst
          Description:Link is used to provide the sources and destinations
          of a link. The type of the property containing the Link XML
          element provides the type of the link. Link is a multi-valued
          element, so multiple Links may be used together to indicate
          multiple links with the same type.
          
          
          2.6.4     Src XML Element
          
          Name: http://www.ietf.org/standards/dav/src
          Purpose: To indicate the source of a link.
          Schema: http://www.ietf.org/standards/dav/
          Parent: http://www.ietf.org/standards/dav/link
          Values= URI
          
          
          2.6.5     Dst XML Element
          
          Name: http://www.ietf.org/standards/dav/Dst
          Purpose: To indicate the destination of a link
          Schema: http://www.ietf.org/standards/dav/
          Parent: http://www.ietf.org/standards/dav/link
          Values= URI
          
          
          2.6.6     Example
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.foocorp.com/Project/" AS = "F"/>
          <D:Prop>
               <Source>
                    <Link>
                         <F:ProjFiles>Source</F:ProjFiles>
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/main.c</dst>
                    </Link>
                    <Link>
                         <F:ProjFiles>Library</F:ProjFiles>
          
          
          
          
          
          
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/main.lib</dst>
                    </Link>
                    <Link>
                         <F:ProjFiles>Makefile</F:ProjFiles>
                         <src>http://foo.bar/program</src>
                         <dst>http://foo.bar/src/makefile</dst>
               <Link>
               </Source>
          </D:Prop>
          
          In this example the resource http://foo.bar/program has a source
          property defined which contains three links. Each link contains
          three elements, two of which, src and dst, are part of the DAV
          schema defined in this document, and one which is defined by the
          schema http://www.foocorp.com/project/ (Source, Library, and
          Makefile). A client which only implements the elements in the DAV
          spec will not understand the foocorp elements and will ignore
          them, thus seeing the expected source and destination links. An
          enhanced client may know about the foocorp elements and be able
          to present the user with additional information about the links.
          
          
          2.7  Multi-Status Response
          
          
          2.7.1     Problem Definition
          
          Some methods effect more than one resource. The effect of the
          method on each of the scoped resources may be different, as such
          a return format that can specify the effect of the method on each
          resource is needed.
          
          
          2.7.2     Solution Requirements
          
          The solution must:
          - communicate the status code and reason
          - give the URI of the resource on which the method was invoked
          - be consistent with other return body formats
          
          2.7.3     Multi-Status Response
          
          The default multi-status response body is an text/xml HTTP entity
          that contains a single XML element called multiresponse, which
          contains a set of XML elements called response, one for each 200,
          300, 400, and 500 series status code generated during the method
          invocation.  100 series status codes MUST NOT be recorded in a
          response XML element.
          
          
          2.7.3.1   MultiResponse
          
          Name: http://www.ietf.org/standards/dav/multiresponse
          Purpose:  Contains multiple response messages.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    1*Response [ResponseDescription]
          Description:The ResponseDescription at the top level is used to
          provide a general message describing the over arching nature of
          the response. If this value is available an application MAY use
          it instead of presenting the individual response descriptions
          contain within the responses.
          
          
          
          
          
          
          2.7.3.2   Response
          
          Name: http://www.ietf.org/standards/dav/response
          Purpose:  Holds a single response
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    (Prop | HREF) Status [ResponseDescription]
          Description: Prop MUST contain one or more empty XML elements
          representing the name of properties. Multiple properties may be
          included if the same response applies to them all. If HREF is
          used then the response refers to a problem with the referenced
          resource, not a property.
          
          
          2.7.3.3   Status
          
          Name: http://www.ietf.org/standards/dav/status
          Purpose:  Holds a single HTTP status-line
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Response
          Value:    status-line   ;status-line defined in [Fielding et al.,
          1997]
          
          
          2.7.3.4   ResponseDescription
          
          Name:
          http://www.ietf.org/standards/dav/ResponseDescription
          Purpose:  Contains a message that can be displayed to the user
          explaining the nature of the response.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Multiresponse and/or Response
          Value:    Any
          Description:   This XML element provides information suitable to
          be presented to a user.
          
          
          2.8  Properties and Methods
          
          
          2.8.1     DELETE
          
          As properties are resources, the deletion of a property causes
          the same result as the deletion of any resource. It is worth
          pointing out that the deletion of a property effects both direct
          manipulation, that is by the property's URL, as well as indirect
          discovery and manipulation, that is PROPPATCH and PROPFIND.
          
          
          2.8.2     GET
          
          A GET with a Request-URI that identifies a property returns the
          name and value of that property.  Accept types may be used to
          specify the format of the return value, but all DAV compliant
          servers MUST at minimum support a return type of text/xml. If
          text/xml is used as the response format then it MUST return the
          name and value of the property using the Prop XML element.
          
          
          2.8.2.1   Example
          
          The following example assumes that the property's URL, originally
          generated by the server, was discovered by examining the proploc
          XML attribute returned on a result from a FINDPROP.
          
          
          
          
          
          
          GET /bar.html;prop=z39.50_authors HTTP/1.1
          Host: foo.com
          
          HTTP/1.1 200 OK
          Content-Type: text/xml
          Content-Length: xxxx
          E-tag: "1234"
          Last-Modified: xxxx
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.w3.com/standards/z39.50/"AS = "Z"/>
          <D:prop>
               <Z:Authors>
                    <Z:Author>Jane Doe</Z:Author>
                    <Z:Author>Joe Doe</Z:Author>
                     <Z:Author>Lots o'Doe</Z:Author>
               </Z:Authors>
          </D:prop>
          
          
          2.8.3     PROPPATCH
          
          The PROPPATCH method processes instructions specified in the
          request body to create and/or remove properties defined on the
          resource identified by Request-URI.
          
          All DAV compliant servers MUST process instructions which are
          specified using the PropertyUpdate, Create, and Remove XML
          elements of the DAV schema.  The request message body MUST
          contain at least one PropertyUpdate XML element.  Instruction
          processing MUST occur in the order instructions are received
          (i.e., from top to bottom), and MUST be performed atomically.
          
          
          2.8.3.1   PropertyUpdate XML element
          
          Name:          http://www.ietf.org/standards/dav/PropertyUpdate
          Purpose:  To contain a request to alter the properties on a
          resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   *(Create | Remove)
          Description:This XML element is a container for the information
          required to modify the properties on the resource. This XML
          element is multi-valued.
          
          
          2.8.3.2   Create XML element
          
          Name:          http://www.ietf.org/standards/dav/create
          Purpose:  To create the DAV properties specified inside the
          Create XML element.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   http://www.ietf.org/standards/dav/PropertyUpdate
          Values=   Prop
          Description:This XML element MUST contain only a Prop XML
          element. The elements contained by Prop specify the name and
          value of properties that are created on Request-URI. If a
          property already exists then its value is replaced. The Prop XML
          element MUST NOT contain a PropLoc XML attribute.
          
          
          2.8.3.3   Remove XML element
          
          
          
          
          
          
          
          Name:          http://www.ietf.org/standards/dav/remove
          Purpose:  To remove the DAV properties specified inside the
          Remove XML element.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   http://www.ietf.org/standards/dav/PropertyUpdate
          Values=   Prop
          Description:Remove specifies that the properties specified in
          Prop should be removed. Specifying the removal of a property that
          does not exist is not an error. All the elements in Prop MUST be
          empty, as only the names of properties to be removed are
          required.
          
          
          2.8.3.4   Response
          
          The response MUST have a response body that contains a
          multiresponse identifying the results for each property.
          
          
          2.8.3.5   Response Codes
          
          200 OK - The command succeeded. As there can be a mixture of
          Create and Removes in a body, a 201 Create seems inappropriate.
          403 Forbidden - The client, for reasons the server chooses not to
          specify, can not alter one of the properties.
          405 Conflict - The client has provided a value whose semantics
          are not appropriate for the property. This includes trying to set
          read only properties.
          413 Request Entity Too Long - If a particular property is too
          long to be recorded then a composite XML error will be returned
          indicating the offending property.
          417 Insufficient Space on Resource - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.
          418 Atomicity Failure - The command was not executed because of
          an atomicity failure elsewhere the caused the entire command to
          be aborted.
          
          
          2.8.3.6   Example
          
          PROPPATCH /bar.html HTTP/1.1
          Host: www.foo.com
          Content-Type: text/xml
          Content-Length: xxxx
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href = "http://www.w3.com/standards/z39.50/" AS = "Z"/>
          <D:PropertyUpdate>
               <Create>
                    <prop>
                         <Z:authors>
                              <Z:Author>Jim Whitehead</Z:Author>
                              <Z:Author>Roy Fielding</Z:Author>
                         </Z:authors>
                    </Prop>
               </Create>
               <Remove>
                    <prop><Z:Copyright-Owner/></prop>
               </Remove>
          </D:PropertyUpdate>
          
          
          
          
          
          
          HTTP/1.1 405 Conflict
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
               href="http://www.ietf.org/standards/dav/" AS = "D"/>
          <?XML:Namespace
               href="http://www.w3.com/standards/z39.50/" AS = "Z"/>
          <D:MultiResponse>
               <ResponseDescription> Copyright Owner can not be deleted or
          altered.</ResponseDescription>
               <Response>
                    <Prop><Z:authors/></Prop>
                    <Status>HTTP/1.1 418 Atomicity Failure</Status>
               </Response>
               <Response>
                    <Prop><Z:Copyright-Owner/></Prop>
                    <Status>HTTP/1.1 405 Conflict</Status>
               </Response>
          </D:MultiResponse>
          
          
          2.8.4     PUT
          
          A PUT is specified in order to control what is returned by a GET.
          However a GET on a property always returns a predefined property
          containment format. Therefore PUT can not be used if the Request-
          URI refers to a property.
          
          
          2.8.5     PROPFIND
          
          The PROPFIND method retrieves properties defined on Request-URI.
          The request message body is an XML document that MUST contain
          only one PropFind XML element, which specifies the type of
          property find action to be performed.  The XML element contained
          by PropFind specifies the type of action to be performed:
          retrieve all property names and values (AllProp), retrieve only
          specified property names and values (Prop), or retrieve only a
          list of all property names (Propname).  When a Prop XML element
          is present, it specifies a list of the names of properties whose
          name and value are to be returned.  The Prop element, when used
          within a FINDPROP request body MUST be empty.
          
          The response is a text/xml message body that contains a
          MultiResponse XML element which describes the results of the
          attempts to retrieve the various properties. If a property was
          successfully retrieved then its value MUST be returned in the
          prop XML element. In the case of Allprop and Findprop, if a
          principal does not have the right to know if a particular
          property exists, an error MUST NOT be returned. The results of
          this method SHOULD NOT be cached.
          
          
          2.8.5.1   Propfind XML element
          
          Name:          http://www.ietf.org/standards/dav/Propfind
          Purpose:  To specify the set of matching properties
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Values=   (Prop | Allprop | Propname)
          Description: Propfind is a container element for the exact
          specification of a PROPFIND request.
          
          
          
          
          
          
          2.8.5.2   Allprop
          
          Name:          http://www.ietf.org/standards/dav/Allprop
          Purpose:  To specify that all properties are to be returned
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Propfind
          Description: Its presence in a PROPFIND request specifies the
          name and value of all properties defined on the resource MUST be
          returned.
          
          
          2.8.5.3   Propname
          
          Name:          http://www.ietf.org/standards/dav/Propname
          Purpose:  To specify that the names of all properties defined on
          the resource are to be returned.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Propfind
          Description: Its presence in a PROPFIND request specifies the
          name of all properties defined on the resource MUST be returned.
          
          
          2.8.5.4   PropFindResult XML element
          
          Name: http://www.ietf.org/standards/dav/PropFindResult
          Purpose: To contain the results of a SEARCH request
          Schema: http://www.ietf.org/standards/dav/
          Parent: Any
          Values: Prop
          
          
          2.8.5.5   Example 1 - Prop
          
          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml
          
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "G"/>
          <?XML:Namespace href =
               "http://www.foo.bar/boxschema/" AS = "B"/>
          <G:PROPFIND>
               <prop>
                    <B:bigbox>
                    <B:author>
                    <B:DingALing>
                    <B:Random>
               </prop>
          </G:PROPFIND>
          
          HTTP/1.1 207 Multi-Response
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
               href ="http://www.ietf.org/standards/dav/" AS = "S">
          <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
          <D:MultiResponse>
               <ResponseDescription> There has been an access violation
          error. </ResponseDescription>
               <Response>
                    <Prop>
                         <R:bigbox D:Proploc="http://prop.com/BoxType">
          
          
          
          
          
          
                              <BoxType>Box type A</BoxType>
                         </R:bigbox>
                         <R:author D:Proploc="http://prop.com/Author">
                              <Name>J.J. Dingleheimerschmidt</Name>
                         </R:author>
                    </Prop>
                    <Status>HTTP/1.1 200 Success</Status>
          </Response>
               <Response>
                    <Prop><R:DingALing/><R:Random/></>
                    <Status>HTTP/1.1 403 Forbidden</Status>
                    <ResponseDescription> The user does not have access to
          the DingALink property. </ResponseDescription>
               </Response>
          </D:MultiResponse>
          
          The result will return all properties on the container. In this
          case only two properties were found. The principal did not have
          sufficient access rights to see the third and fourth properties
          so an error was returned.
          
          
          2.8.5.6   Example 2 - Allprop
          
          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "G"/>
          <G:PROPFIND>
               <Allprop/>
          </G:PROPFIND>
          
          HTTP/1.1 200 Success
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" As = "S">
          <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
          <S:MultiResponse>
               <Prop>
                    <R:bigbox D:Proploc="http://prop.com/BigBox">
                         <BoxType>Box type A</BoxType>
                    </R:bigbox>
                    <R:author D:Proploc="http://prop.com/Author">
                         <Name>Hadrian</Name>
                    </R:author>
               </Prop>
               <Status>HTTP/1.1 200 Success</Status>
          </S:MultiResponse>
          
          This particular client only had the right to see two properties,
          BoxType and Author. No error is returned for the remaining
          properties, as the client does not even have sufficient rights to
          know they exist. If the client did have the right to know they
          existed but did not have the right to see their value, a 207
          multi-response with a multiresponse, as used in the previous
          example, would have been returned.
          
          
          2.8.5.7   Example 3 - Propname
          
          
          
          
          
          
          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" AS = "G"/>
          <G:PROPFIND>
               <Propname/>
          </G:PROPFIND>
          
          HTTP/1.1 200 Success
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" As = "S">
          <?XML:Namespace
               href = "http://www.foo.bar/boxschema" AS = "R">
          <S:MultiResponse>
               <Prop>
                    <R:bigbox D:Proploc="http://prop.com/BigBox"/>
                    <R:author D:Proploc="http://prop.com/Author"/>
                    <R:DingALing/>
                    <R:Random/>
               </Prop>
               <Status>HTTP/1.1 200 Success</Status>
          </S:MultiResponse>
          
          In this case only two of the properties have direct URLs
          available, while the other two properties can only be referenced
          via PROPFIND and PROPPATCH.
          
          
          3    A Proposal for Collections of Web Resources and Name Space
             Operations
          
          3.1  Observations on the HTTP Object Model
          
          This section provides a description of a new type of Web
          resource, the collection, and discusses its interactions with the
          HTTP URL namespace.  This discussion is a prerequisite for the
          specification of methods that operate on collections, given later
          in this document.
          
          
          3.1.1     Collection Resources
          
          A collection is a resource whose state consists of a list of
          internal members, a list of external members, and a set of
          properties.  An internal member resource MUST have a URI that is
          immediately relative to the base URI of the collection, that is,
          a relative URI in which "../" is illegal, which must begin with
          "./" and which MAY contain only one other "/" at the end of the
          URI. An external member resource MUST be an absolute URI that is
          not an internal URI.  Any given internal or external URI MUST
          only belong to the collection once, i.e., multiple instances of
          URIs in a collection are illegal.  Properties defined on
          collections have no special distinction, and behave exactly as do
          properties on non-collection resources.
          
          The purpose of a collection resource is to model collection-like
          objects (e.g., a filesystem directory) within a server's
          namespace.  Once these objects have been modeled with
          collections, a client may perform an INDEX, add and remove
          
          
          
          
          
          
          external members using ADDREF and DELREF, and perform recursive
          operations, such as a full hierarchy copy.
          
          To support methods which operate on collections, a server SHOULD
          model its collection-like objects with collection resources.  For
          example, a server which is implemented on top of a filesystem
          SHOULD treat all filesystem directories exposed by the server as
          collection resources.
          
          
          3.1.2     Creation and Retrieval of Collection Resources
          
          This document specifies the MKCOL method to create new collection
          resources, and the INDEX method to list their contents.
          
          In HTTP/1.1, the PUT method is defined to store the request body
          at the location specified by Request-URI.  While a description
          format for a collection can readily be constructed that could be
          used with PUT, the implications of sending such a description to
          the server are undesirable.  For example, if a description of a
          collection that omitted some existing resources were PUT to a
          server, this might be interpreted as a command to remove those
          members.  This would extend PUT to perform DELETE functionality,
          which is undesirable since it changes the semantics of PUT, and
          makes it difficult to control DELETE functionality with an access
          control scheme based on methods.
          
          While the POST method is sufficiently open-ended that a "create a
          collection" POST command could be constructed, this is
          undesirable because it would be difficult to separate access
          control for collection creation from other uses of POST if they
          both use the same method.
          
          While it might seem desirable to have GET return a listing of the
          members of a collection, this is foiled by the existence of the
          "index.html" de-facto standard namespace redirection, in which a
          GET request on a collection is automatically redirected to the
          index.html resource.
          
          The exact definition of the behavior of GET and PUT on
          collections is defined later in this document.
          
          
          3.1.2.1   Example
          
          The structured resource http://foo/bar is created with a PUT. Bar
          is a multipart/related file with two members http://foo/bar/a and
          http://foo/bar/b. If bar were deleted then both a and b would
          also be deleted since they are all really just one resource. If
          http://foo/bar/a/c was PUT then a DELETE on http://foo/bar/a
          would also delete http://foo/bar/a/c as c was created with a PUT
          not a MKCOL.
          
          If http://foo/bar/b/d is created with a MKCOL and
          http://foo/bar/b/d/e was created then a DELETE on d would fail
          because d is a collection with an internal member. However the
          existence of the collection d is something of an illusion. If a
          DELETE was executed on http://foo/bar then everything would be
          deleted, even though http://foo/bar/b/d was created with a MKCOL.
          
          Thus the effect of a MKCOL within a composite resource’s
          namespace is felt on its children, not its ancestors. The
          children of d MUST be treated as members of a collection when a
          method is executed on d. But a method executed on b or a is
          treated as if there only existed a non-collection resource.
          
          
          
          
          
          
          
          
          3.1.3     Source Resources and Output Resources
          
          For many resources, the entity returned by GET exactly matches
          the persistent state of the resource, for example, a GIF file
          stored on a disk.  For this simple case, the URL at which a
          resource is accessed is identical to the URL at which the source
          (the persistent state) of the resource is accessed. This is also
          the case for HTML source files that are not processed by the
          server prior to transmission.
          
          However, the server can sometimes process HTML resources before
          they are transmitted as a return entity body. For example,
          server-side-include directives within an HTML file instruct a
          server to replace the directive with another value, such as the
          current date.  In this case, what is returned by GET (HTML plus
          date) differs from the persistent state of the resource (HTML
          plus directive). Typically there is no way to access the HTML
          resource containing the unprocessed directive.
          
          Sometimes the entity returned by GET is the output of a data-
          producing process that is described by one or more source
          resources (that may not even have a location in the URL
          namespace).  A single data-producing process may dynamically
          generate the state of a potentially large number of output
          resources. An example of this is a CGI script that describes a
          "finger" gateway process that maps part of the namespace of a
          server into finger requests, such as
          http://www.foo.bar.org/finger_gateway/user@host.
          
          In the absence of distributed authoring capability, it is
          acceptable to have no mapping of source resource(s) to the URI
          namespace, and in fact has desirable security benefits. However,
          if remote editing of the source resource(s) is desired, the
          source resource(s) should be given a location in the URI
          namespace. This source location should not be one of the
          locations at which the generated output is retrievable, since in
          general it is impossible for the server to differentiate requests
          for source resources from requests for process output resources.
          There is often a many-to-many relationship between source
          resources and output resources.
          
          For DAV compliant servers all output resources which have a
          single source resource (and that source resource has a URI), the
          URI of the source resource SHOULD be stored in a single link on
          the output resource with type
          http://www.ietf.org/standards/dav/source. Note that by storing
          the source URI in links on the output resources, the burden of
          discovering the source is placed on the authoring client.
          
          
          3.2  MKCOL Method
          
          
          3.2.1     Problem Description
          
          A client must be able to create a collection.
          
          
          3.2.2     Solution Requirements
          
          The solution must ensure that a collection has been made (i.e.
          that it responds to the INDEX method) as opposed to a non-
          
          
          
          
          
          
          collection resource. If a collection could not be made, it must
          indicate this failure to the user-agent.
          
          
          3.2.3     Request
          
          MKCOL creates a new collection resource at the location specified
          by the Request-URI. If the Request-URI exists, then MKCOL must
          fail. During MKCOL processing, a server MUST make the Request-URI
          a member of its parent collection. If no such an ancestor exists,
          the method MUST fail. When the MKCOL operation creates a new
          collection resource, all ancestors MUST already exist, or the
          method MUST fail with a 409 Conflict status code.  For example,
          if a request to create collection /a/b/c/d/ is made, and neither
          /a/b/ nor /a/b/c/ exist, the request MUST fail.
          
          
          3.2.3.1   MKCOL Without Request Body
          
          When MKCOL is invoked without a request body, the newly created
          collection has no members.
          
          
          3.2.3.2   MKCOL With Request Body
          
          A MKCOL request message MAY contain a message body.  The behavior
          of a MKCOL request when the body is present is limited to
          creating collections, members of a collection, bodies of members
          and properties on the collections or members. If the server
          receives a MKCOL request entity type it does not support or
          understand it MUST respond with a 415 (Unsupported Media Type)
          status code.  The exact behavior of MKCOL for various request
          media types is undefined in this document, and will be specified
          in separate documents.
          
          
          3.2.4     Response
          
          Responses from a MKCOL request are not cacheable, since MKCOL has
          non-idempotent semantics.
          201 (Created) - The collection or structured resource was created
          in its entirety.
          403 (Forbidden) - This indicates at least one of two conditions:
          1) The server does not allow the creation of collections at the
          given location in its namespace, and 2) The parent collection of
          the Request-URI exists but cannot accept members.
          409 (Conflict) - A collection cannot be made at the Request-URI
          until one or more intermediate collections have been created.
          415 (Unsupported Media Type)- The server does not support the
          request type of the body.
          417 (Insufficient Space on Resource) - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.
          
          
          3.2.5     Example
          
          This example creates a container collection called
          /webdisc/xfiles/ on the server www.server.org.
               MKCOL /webdisc/xfiles/ HTTP/1.1
               Host: www.server.org
          
          
               HTTP/1.1 201 Created
          
          
          
          
          
          
          
          3.3  Standard DAV Properties
          
          The following properties are defined on DAV compliant resources.
          All enclosed properties are part of the DAV Schema.
          
          
          3.3.1     IsCollection Property
          
          Name:     http://www.ietf.org/standards/dav/iscollection
          Purpose:  This property contains a Boolean value that is set to
          "true" if the resource is a collection
          Schema:   http://www.ietf.org/standards/dav/
          Value:    ("true" | "false")
          Description: This property MUST be defined on all DAV compliant
          resources.
          
          
          3.3.2     DisplayName Property
          
          Name: http://www.ietf.org/standards/dav/displayname
          Purpose:  A name for the resource that is suitable for
          presentation to a user.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Any valid XML character data (as defined in [Bray,
          Sperberg-McQueen, 1997])
          Description: This property SHOULD be defined on all DAV compliant
          resources. If present, the property contains a description of the
          resource that is suitable for presentation to a user.
          
          
          3.3.3     CreationDate Property
          
          Name: http://www.ietf.org/standards/dav/creationdate
          Purpose:  The time and date the resource was created.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    The time and date MUST be given in ISO 8601 format
          [ISO8601]
          Description: This property SHOULD be defined on all DAV compliant
          resources. If present, it contains a timestamp of the moment when
          the resource was created (i.e., the moment it had non-null
          state).
          
          
          3.3.4     GETentity Property
          
          Name: http://www.ietf.org/standards/dav/GETentity
          Purpose:  Contains the value of headers that are returned by a
          GET without Accept headers.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Content-Type Content-Length Content-Language Last-
          Modified Etag Creation-Date
          Description: This property MUST be defined on all DAV compliant
          resources unless GET is not supported, in which case this
          property MUST NOT be defined. This property MUST contain at most
          one instance of each element in its Value, if they are defined.
          
          3.3.5     INDEXentity Property
          
          Name: http://www.ietf.org/standards/dav/INDEXentity
          Purpose:  Contains the value of headers that are returned by an
          INDEX.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    Content-Type Content-Length Content-Language Last-
          Modified Etag Creation-Date
          
          
          
          
          
          
          Description: This property MUST be defined on all DAV compliant
          resources unless INDEX is not supported, in which case this
          property MUST NOT be defined. This property MUST contain at most
          one instance of each element in its Value, if they are defined.
          
          
          3.3.6     Content-Type XML Element
          
          Name: http://www.ietf.org/standards/dav/content-type
          Purpose:  The content-type of the member resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   GETentity or INDEXentity
          Value:    media-type   ; defined in Section 3.7 of [Fielding et
          al., 1997]
          Description: If the parent of this element is GETentity, the
          value MUST be identical to the content-type returned by a GET on
          the resource without Accept headers.  If the parent is
          INDEXentity, the value MUST be identical to the content-type
          returned by an INDEX on the resource.  If no content-type is
          available, this element MUST NOT be defined.
          
          
          3.3.7     Content-Length XML Element
          
          Name:          http://www.ietf.org/standards/dav/content-length
          Purpose:  Describes the default content-length of the resource.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    content-length ; see section 14.14 of RFC 2068
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the content-length header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the
          content-length returned by an INDEX on the resource.  If no
          content-length is available, this element MUST NOT be defined.
          
          
          3.3.8     Content-Language XML Element
          
          Name:          http://www.ietf.org/standards/dav/content-language
          Purpose:  Describes the default natural language of a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Value:    language-tag   ;language-tag is defined in section
          14.13 of RFC 2068
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the content-language header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the
          content-language header returned by an INDEX on the resource.  If
          no content-language header is available, this element MUST NOT be
          defined.
          
          
          3.3.9     Last-Modified XML Element
          
          Name:     http://www.ietf.org/standards/dav/last-modified
          Purpose:  The date the resource was last modified.
          Schema:        http://www.ietf.org/standards/dav/
          Parent:        GETentity or INDEXentity
          Value:    The date MUST be given in RFC 1123 format using the
          rfc-1123  production, defined in section 3.3.1 of [Fielding et al.,
          1997].
          Description: If the parent of this element is GETentity, this
          
          
          
          
          
          
          element MUST have a value equal to the last-modified header
          returned by a GET on the resource without Accept headers.  If the
          parent is INDEXentity, the value MUST be identical to the last-
          modified header returned by an INDEX on the resource.  If no
          last-modified header is available, this element MUST NOT be defined.
          
          
          3.3.10    Etag XML Element
          
          Name: http://www.ietf.org/standards/dav/etag
          Purpose:  The entity tag of the resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   GETentity or INDEXentity
          Value:    entity-tag  ; defined in Section 3.11 of [Fielding et
          al., 1997]
          Description: If the parent of this element is GETentity, this
          element MUST have a value equal to the entity-tag header returned
          by a GET on the resource without Accept headers.  If the parent
          is INDEXentity, the value MUST be identical to the entity-tag
          header returned by an INDEX on the resource.  If no entity-tag
          header is available, this element MUST NOT be defined.
          
          
          3.4  INDEX Method
          
          
          3.4.1     Problem Description
          
          A mechanism is needed to discover if a resource is a collection
          and if so, list its members.
          
          
          3.4.2     Solution Requirements
          
          The solution:
          - must allow a client to discover the members of a collection
          - must always provide a machine-readable description of the
            membership of a collection
          - must be leveraged as a more general mechanism to provide a
            list of contents for any resource which can profitably return a
            membership like listing.
          
          
          3.4.3     The Request
          
          The INDEX method returns a machine-readable representation of the
          membership of the resource at the Request-URI.
          
          For a collection, INDEX MUST return a list of its members. All
          WebDAV compliant resources MUST support the text/xml response
          entity described below.  The INDEX result for a collection MAY
          also return a list of the members of child collections, to any
          depth.
          
          Collections that respond to an INDEX method with a text/xml
          entity MUST contain only one ResInfo element.  This ResInfo
          element contains an Href element, which gives the identifier(s)
          of the resource, a Prop element, which gives selected properties
          of the resource, and a Members element, which contains a ResInfo
          element for each member of the collection.  The Prop element MUST
          
          
          
          
          
          
          contain at least the following properties, if they are defined
          and available: DisplayName, IsCollection, CreationDate,
          GETentity, and INDEXentity.
          
          The response from INDEX is cacheable, and SHOULD be accompanied
          by an ETag header (see section 13.3.4 of RFC 2068). If GET and
          INDEX return different entities for the same resource state, they
          MUST return different entity tags.
          
          
          3.4.4     The Response
          
          200 (OK) - The server MUST send a machine readable response
          entity which describes the membership of the resource.
          
          
          3.4.5     ResInfo XML Element
          
          Name:     http://www.ietf.org/standards/dav/resinfo
          Purpose:  Describes a resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    Href Prop Members
          Description: There MUST be at least one Href element.  Each Href
          element contains a URI for the resource, which MUST be an
          absolute URI. There MUST be a single Prop element that contains a
          series of properties defined on the resource.  If the resource is
          a collection, it MAY have at most one Members element, which
          describes the members of the collection.
          
          
          3.4.6     Members XML Element
          
          Name: http://www.ietf.org/standards/dav/members
          Purpose:  Describes the membership of a collection resource.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   ResInfo
          Value:    ResInfo
          Description: Contains zero or more ResInfo elements, which
          describe members of the collection.
          
          
          3.4.7     Href XML Element
          
          Name: http://www.ietf.org/standards/dav/href
          Purpose:  To identify that the content of the element is a URI.
          Schema:   http://www.ietf.org/standards/dav/
          Parent:   Any
          Value:    URI ; See section 3.2.1 of [Fielding et al., 1997]
          
          3.4.8     Example
          
          INDEX /user/yarong/dav_drafts/ HTTP/1.1
          Host: www.microsoft.com
          
          HTTP/1.1 200 OK
          Content-Type: text/xml
          Content-Length: xxx
          Last-Modified: Thu, 11 Sep 1997 23:45:12 GMT
          ETag: "fooyyybar"
          
          <?XML:Namespace
               href = "http://www.ietf.org/standards/dav/" as = "D"/>
          
          
          
          
          
          
          <D:ResInfo>
               <XML:Href>
                    http://www.microsoft.com/user/yarong/dav_drafts/
               </XML:Href>
               <Prop>
                  <DisplayName>
                    WebDAV working drafts directory
                  </DisplayName>
                  <IsCollection>true</IsCollection>
                  <CreationDate>19970418T070304Z</CreationDate>
                  <GETentity>
                    <Content-Type>text/html</Content-Type>
                    <Content-Length>2754</Content-Length>
                    <Content-Language>en</Content-Language>
                    <Last-Modified>
                         Fri, 22 Aug 1997 10:11:26 GMT
                    </Last-Modified>
                    <Etag>"8675309"</Etag>
                  </GETentity>
                  <INDEXentity>
                    <Content-Type>text/xml</Content-Type>
                    <Content-Length>xxx</Content-Length>
                    <Last-Modified>
                         Thu, 11 Sep 1997 23:45:12 GMT
                    </Last-Modified>
                    <Etag>"fooyyybar"</Etag>
                  </INDEXentity>
               </Prop>
          
               <Members>
                  <ResInfo>
                    <XML:Href>
                    http://www.microsoft.com/user/yarong/dav_drafts/base
                    </XML:Href>
                    <Prop>
                       <IsCollection
               D:PropLoc="http://www.microsoft.com/user/yarong/dav_drafts/b
               ase;props=IsCollection">
                         False
                       </IsCollection>
                       <DisplayName>
                         WebDAV Name Space Operations Draft
                       </DisplayName>
                       <Creation-Date>19970320T230525Z</Creation-Date>
          
                       <GETentity>
                         <Content-Type>application/msword</Content-Type>
                         <Content-Length>1400</Content-Length>
                         <Content-Language>en</Content-Language>
                         <Last-Modified>
                              Fri, 22 Aug 1997 18:22:56 GMT
                         </Last-Modified>
                         <Etag>"8675309"</Etag>
                       </GETentity>
                    </Prop>
                  </ResInfo>
               </Members>
          </D:ResInfo>
          
          This example shows the result of the INDEX method applied to the
          collection resource
          http://www.microsoft.com/user/yarong/dav_drafts/.  It returns a
          response body in XML format, which gives information about the
          container and its sole member,
          http://www.microsoft.com/user/yarong/dav_drafts/base. The entry
          
          
          
          
          
          
          on the collection confirms that the resource the INDEX was
          executed on is a collection. The result also contains the URI of
          the IsCollection property on the member resource.
          
          
          3.5  Behavior of RFC 2068 Methods on Collections
          
          With the introduction of the collection resource type to the HTTP
          object model, it is necessary to define the behavior of the
          existing methods (defined in RFC 2068) when invoked on a
          collection resource to avoid ambiguity.  While some methods, such
          as OPTIONS and TRACE behave identically when applied to
          collections, GET, HEAD, POST, PUT, and DELETE require some
          additional explanation.
          
          
          3.5.1     GET, HEAD for Collections
          
          The semantics of GET are unchanged when applied to a collection,
          since GET is defined as, "retrieve whatever information (in the
          form of an entity) is identified by the Request-URI" [Fielding et
          al., 1997]. GET when applied to a collection MAY return the
          contents of an "index.html" resource, a human-readable view of
          the contents of the collection, or something else altogether, and
          hence it is possible the result of a GET on a collection will
          bear no correlation to the state of the collection.
          
          Similarly, since the definition of HEAD is a GET without a
          response message body, the semantics of HEAD are unmodified when
          applied to collection resources.
          
          
          3.5.2     POST for Collections
          
          Since by definition the actual function performed by POST is
          determined by the server and often depends on the particular
          resource, the behavior of POST when applied to collections cannot
          be meaningfully modified because it is largely undefined.  Thus
          the semantics of POST are unmodified when applied to a
          collection.
          
          
          3.5.3     PUT for Collections
          
          As defined in the HTTP/1.1 specification [Fielding et al., 1997],
          the "PUT method requests that the enclosed entity be stored under
          the supplied Request-URI."  Since submission of an entity
          representing a collection would implicitly encode creation and
          deletion of resources, this specification intentionally does not
          define a transmission format for creating a collection using PUT.
          Instead, the MKCOL method is defined to create collections.  If a
          PUT is invoked on a collection resource it MUST fail.
          
          When the PUT operation creates a new non-collection resource all
          ancestors MUST already exist.  If all ancestors do not exist, the
          method MUST fail with a 409 Conflict status code.  For example,
          if resource /a/b/c/d.html is to be created and /a/b/c/ does not
          exist, then the request MUST fail.
          
          
          3.5.3.1   PUT for Non-Collection Resources
          
          A PUT performed on an existing resource replaces the GET response
          entity of the resource, but MUST NOT change the value of any dead
          properties defined on the resource.  Live properties defined on
          
          
          
          
          
          
          the resource MAY be recomputed during PUT processing.
          
          
          3.5.4     DELETE for Collections
          
          When DELETE is applied to a collection without internal members
          the collection resource, along with its properties, and external
          members, MUST be deleted.  A DELETE method applied to a
          collection resource containing internal member resources MUST
          fail with a 409 Conflict status code.
          
          
          3.5.5     DELETE Method for Non-Collection Resources
          
          If the DELETE method is issued to a non-collection resource which
          is an internal member of a collection, then during DELETE
          processing a server MUST remove the Request-URI from its parent
          collection. A server MAY remove the URI of a deleted resource
          from any collections of which the resource is an external member.
          
          
          3.6  COPY Method
          
          
          3.6.1     Problem Description
          
          Currently, in order to create a copy of a resource, the client
          must GET an entity and then PUT that entity to the desired
          destination. This requires (1) an entity to be transmitted to and
          from the server and (2) that the resource be expressible as an
          entity with complete fidelity.
          
          This is problematic because of the network traffic involved in
          making a copy, and because there is often no way to fully express
          a resource as an entity without a loss of fidelity.
          
          
          3.6.2     Solution Requirements
          
          The solution:
          - MUST allow a principal to create a copy of a resource
            without having to transmit the resource to and from the server.
          
          
          3.6.3     The Request
          
          The COPY method creates a duplicate of the source resource, given
          by the Request-URI, in the destination resource, given by the
          Destination header.  The Destination header MUST be present.  The
          exact behavior of the COPY method depends on the type of the
          source resource.
          
          
          3.6.3.1   COPY for HTTP/1.1 resources
          
          When the source resource is not a collection, and is not a
          property, the body of the destination resource MUST be octet-for-
          octet identical to the body of the source resource. Alterations
          to the destination resource do not modify the source resource.
          Alterations to the source resource do not modify the destination
          resource. Thus, all copies are performed "by-value".
          
          All properties on the source resource MUST be duplicated on the
          destination resource, subject to modifying headers, following the
          definition for copying properties.
          
          
          
          
          
          
          
          
          3.6.3.2   COPY for Properties
          
          The following section defines how properties on a resource are
          handled during a COPY operation.
          Live properties SHOULD be duplicated as identically behaving live
          properties at the destination resource. Since they are live
          properties, the server determines the syntax and semantics (hence
          value) of these properties.  Properties named by the Enforce-
          Live-
          Properties header MUST be live on the destination resource, or
          the method MUST fail.  If a property is not named by Enforce-
          Live-
          Properties and cannot be copied live, then its value MUST be
          duplicated, octet-for-octet, in an identically named, dead
          resource on the destination resource.
          
          If a property on the source already exists on the resource and
          the overwrite header is set to TRUE then the property at the
          destination MUST be overwritten with the property from the
          source. If the overwrite header is false and the previous
          situation exists then the COPY MUST fail with a 409 Conflict.
          
          
          3.6.3.3   COPY for Collections
          
          A COPY on a collection causes a new, empty collection resource to
          be created at the destination with the same properties as the
          source resource.  All properties on the source collection MUST be
          duplicated on the destination collection, subject to modifying
          headers, following the definition for copying properties.  The
          new collection MUST NOT contain any members, internal or
          external.
          
          
          3.6.3.4   Type Interactions
          
          If the destination resource identifies a property and the source
          resource is not a property, then the copy SHOULD fail.
          
          If the destination resource identifies a collection and the
          Overwrite header is "true," prior to performing the copy, the
          server MUST perform a DELETE operation on the collection.
          
          
          3.6.4     The Response
          
          200 (OK) The source resource was successfully copied to a pre-
          existing destination resource.
          
          201 (Created) The source resource was successfully copied.  The
          copy operation resulted in the creation of a new resource.
          
          412 (Precondition Failed) This status code MUST be returned if
          the server was unable to maintain the liveness of the properties
          listed in the Enforce-Live-Properties header, or if the Overwrite
          header is false, and the state of the destination resource is
          non-null.
          
          417 (Insufficient Space on Resource) - The destination resource
          does not have sufficient space to record the state of the
          resource after the execution of this method.
          
          500 (Server Error) The resource was in such a state that it could
          not be copied. This may occur if the Destination header specifies
          a resource that is outside the namespace the resource is able to
          interact with.
          
          
          
          
          
          
          
          
          3.6.5     Examples
          
          
          3.6.5.1   Overwrite Example
          
          This example shows resource
          http://www.ics.uci.edu/~fielding/index.html being copied to the
          location http://www.ics.uci.edu/users/f/fielding/index.html.  The
          contents of the destination resource were overwritten, if non-
          null.
          
          COPY /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html
          
          
          HTTP/1.1 200 OK
          
          
          3.6.5.2   No Overwrite Example
          
          The following example shows the same copy operation being
          performed, except with the Overwrite header set to "false."  A
          response of 412, Precondition Failed, is returned because the
          destination resource has a non-null state.
          
          COPY /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html
          Overwrite: "false"
          
          
          HTTP/1.1 412 Precondition Failed
          
          
          
          
          3.7  MOVE Method
          
          
          3.7.1     Problem Description
          
          The move operation on a resource is the logical equivalent of a
          copy followed by a delete, where the actions are performed
          atomically.  Using RFC 2068 methods only, this procedure could be
          performed in several steps. First, the client could issue a GET
          to retrieve a representation of a resource, issue a DELETE to
          remove the resource from the server, then use PUT to place the
          resource on the server with a new URI. As is the case for COPY -
          because of the network traffic involved in making a move, and
          because there is often no way to fully express a resource as an
          entity without a loss of fidelity - server move functionality is
          preferable.
          
          With a WEBDAV server, a principal may accomplish this task by
          issuing a COPY and then DELETE. Network load decreases, but the
          server load may still be significant because the server must
          create a duplicate resource. Were a server to know beforehand
          that a principal intended to perform COPY and DELETE operations
          in succession, it could avoid the creation of a duplicate
          resource.
          
          
          
          
          
          
          
          3.7.2     Solution Requirements
          
          The solution:
          - Must prevent the unneeded transfer of entity bodies from and
            to the server.
          - Must prevent the unneeded creation of copies by the server.
          
          
          3.7.3     The Request
          
          The move operation on a resource is the logical equivalent of a
          copy followed by a delete, where the actions are performed
          atomically. If a resource exists at the destination, the
          destination resource will be DELETEd as a side effect of the MOVE
          operation, subject to the restrictions of the overwrite header.
          
          
          3.7.4     The Response
          
          200 (OK) - The resource was moved. A successful response must
          contain the Content-Location header, set equal to the URI in
          source. This lets caches properly flush any cached entries for
          the source. Unfortunately the Content-Location header only allows
          a single value so it is not possible for caches unfamiliar with
          the MOVE method to properly clear their caches.
          
          412 (Precondition Failed) This status code MUST be returned if
          the server was unable to maintain the liveness of the properties
          listed in the Enforce-Live-Properties header, or if the Overwrite
          header is false, and the state of the destination resource is
          non-null.
          
          501 (Not Implemented) - This may occur if the Destination header
          specifies a resource which is outside its domain of control
          (e.g., stored on another server) resource and the server either
          refuses or is incapable of moving to an external resource.
          
          502 (Bad Gateway) - This may occur when moving to external
          resources and the destination server refused to accept the
          resource.
          
          
          3.7.5     Examples
          
          
          3.7.5.1   Overwrite Example
          
          This example shows resource
          http://www.ics.uci.edu/~fielding/index.html being moved to the
          location http://www.ics.uci.edu/users/f/fielding/index.html.  The
          contents of the destination resource were overwritten, if non-
          null.
          
          MOVE /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html
          
          
          HTTP/1.1 200 OK
          Content-Location:
          http://www.ics.uci.edu/users/f/fielding/index.html
          
          
          
          
          
          
          3.8  ADDREF Method
          
          
          3.8.1     Problem Definition
          
          There needs to be a way to add an external member to a
          collection.
          
          
          3.8.2     Solution Requirements
          
          The solution must:
          -    allow access control
          -    allow referencing to URIs of external members
          -    not require a body
          
          
          3.8.3     The Request
          
          The ADDREF method adds the URI specified in the Collection-Member
          header as an external member to the collection specified by the
          Request-URI. The value in the Collection-Member header MUST be an
          absolute URI meeting the requirements of an external member URI.
          
          It is not an error if the URI specified in the Collection-Member
          header already exists as an external member of the collection,
          however, after processing ADDREF there MUST be only one instance
          of the URI in the collection.  If the URI specified in the
          Collection-Member header already exists as an internal member of
          the collection, the ADDREF method MUST fail with a 412
          Precondition Failed status code.
          
          
          3.8.4     Example
          
          ADDREF /~whitehead/dav/ HTTP/1.1
          HOST: www.ics.udi.edu
          Collection-Member: http://www.ietf.org/standards/dav/
          
          
          HTTP/1.1 200 OK
          
          
          3.9  DELREF Method
          
          
          3.9.1     Problem Definition
          
          There needs to be a way to remove an external member from a
          collection.
          
          
          3.9.2     Solution Requirements
          
          The solution must:
          - allow access control
          - allow referencing to URIs of external members
          - not require a body
          
          
          3.9.3     The Request
          
          The DELREF method removes the URI specified in the Collection-
          Member header from the collection specified by the Request-URI.
          
          
          
          
          
          
          DELREFing a URI which is not a member of the collection is not an
          error. DELREFing an internal member MUST fail with a 412
          Precondition Failed status code.
          
          
          3.9.4     Example
          
          DELREF /~whitehead/dav/ HTTP/1.1
          Host: www.ics.udi.edu
          Collection-Member: http://www.ietf.org/standards/dav/
          
          
          HTTP/1.1 200 OK
          
          
          3.10 PATCH Method
          
          
          3.10.1    Problem Definition
          
          At present, if a principal wishes to modify a resource, they must
          issue a GET against the resource, modify their local copy of the
          resource, and then issue a PUT to place the modified resource on
          the server. This procedure is inefficient because the entire
          entity for a resource must be transmitted to and from the server
          in order to make even small changes.  Ideally, the update entity
          transmitted to the server should be proportional in size to the
          modifications.
          
          
          3.10.2    Solution Requirements
          
          The solution must:
          -    allow partial modification of a resource without having to
               transmit the entire modified resource
          -    allow byte-range patching
          -    allows extensions so that patches can be done beyond simple
               byte-range patching
          -    allow ranges to be deleted, inserted, and replaced
          
          
          3.10.3    The Request
          
          The request entity of the PATCH method contains a list of
          differences between the resource identified by the Request-URI
          and the desired content of the resource after the PATCH action
          has been applied.  The list of differences is in a format defined
          by the media type of the entity (e.g., "application/diff") and
          must include sufficient information to allow the server to
          convert the original version of the resource to the desired
          version.  Processing performed by PATCH is atomic, hence all
          changes MUST be successfully executed or the method fails. PATCH
          MUST fail if executed on a non-existent resource; i.e. PATCH does
          not create a resource as a side effect.
          
          If the request appears (at least initially) to be acceptable, the
          server MUST transmit an interim 100 response message after
          receiving the empty line terminating the request headers and
          continue processing the request.  Since the semantics of PATCH
          are non-idempotent, responses to this method are not cacheable.
          
          While server support for PATCH is optional, if a server does
          support PATCH, it MUST support at least the text/xml diff format
          defined below.  Support for the VTML difference format [VTML] is
          recommended, but not required.
          
          
          
          
          
          
          
          
          3.10.4    text/xml elements for PATCH
          
          The resourceupdate XML element contains a set of XML sub-entities
          that describe modification operations.  The name and meaning of
          these XML elements is given below. Processing of these directives
          MUST be performed in the order encountered within the XML
          document.  A directive operates on the resource as modified by
          all previous directives (executed in sequential order). The
          length of the resource MAY be extended or reduced by a PATCH.
          
          The changes specified by the resourceupdate XML element MUST be
          executed atomically.
          
          
          3.10.4.1  ResourceUpdate
          
          Name:     http://www.ietf.org/standards/dav/patch/resourceupdate
          Purpose:       Contains an ordered set of changes to a non-
          collection, non-property resource.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        Any
          Value:         *(Insert | Delete | Replace)
          
          
          3.10.4.2  Insert
          
          Name:     http://www.ietf.org/standards/dav/patch/insert
          Purpose:       Insert the XML element’s contents starting at the
          specified octet.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The insert XML element MUST contain an Octet-Range
          XML element that specifies an octet position within the body of a
          resource.  A value of "end" specifies the end of the resource.
          The body of the insert XML element contains the octets to be
          inserted.
          
          Please note that in order to protect the white space contained in
          this XML element the following attribute/value MUST be included
          in the element: XML-SPACE = "PRESERVE".
          
          
          3.10.4.3  Delete
          
          Name:     http://www.ietf.org/standards/dav/patch/delete
          Purpose:       Removes the specified range of octets.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The Delete XML element MUST contain an octet-range
          XML element.
          
          Discussion: The octets that are deleted are removed, which means
          the resource is collapsed and the length of the resource is
          decremented by the size of the octet range.  It is not
          appropriate to replace deleted octets with zeroed-out octets,
          since zero is a valid octet value.
          
          
          3.10.4.4  Replace
          
          Name:     http://www.ietf.org/standards/dav/patch/replace
          Purpose:       Replaces the specified range of octets with the
          contents of the XML element.  If the number of octets in the XML
          
          
          
          
          
          
          element is different from the number of octets specified, the
          update MUST be rejected.
          Schema:        http://www.ietf.org/standards/dav/patch/
          Parent:        ResourceUpdate
          Value:         The Replace XML element MUST contain an octet-
          range XML element. The contents of the entity are the replacement
          octets.
          
          Please note that in order to protect the white space contained in
          this XML element the following attribute/value MUST be included
          in the element: XML-SPACE = "PRESERVE".
          
          
          3.10.4.5  Octet-Range Attribute
          
          Name:          http://www.ietf.org/standards/dav/patch/octet-
          range
          Purpose:  Specifies a range of octets that the enclosing property
          effects.
          Schema:   http://www.ietf.org/standards/dav/patch/
          Parent:   Insert, Delete, Replace
          Value:    number ["-" (number | "end")]
                    Number = 1*Digit
          
          Description: Octet numbering begins with 0. If the octet contains
          a single number then the operation is to begin at that octet and
          to continue for a length specified by the operation. In the case
          of a delete, this would mean to delete a single octet. In the
          case of an insert this would mean to begin the insertion at the
          specified octet and to continue for the length of the included
          value, extending the resource if necessary. In the case of
          replace, the replace begins at the specified octet and overwrites
          all that follow to the length of the included value.
          
          
          3.10.5    The Response
          
          200 (OK) - The request entity body was processed without error,
          resulting in an update to the state of the resource.
          
          409 (Conflict) - If the update information in the request message
          body does not make sense given the current state of the resource
          (e.g., an instruction to delete a non-existent line), this status
          code MAY be returned.
          
          415 (Unsupported Media Type) - The server does not support the
          content type of the update instructions in the request message
          body.
          
          416 (Unprocessable Entity) - A new status code.  The server
          understands the content type of the request entity, but was
          unable to process the contained instructions.
          
          417 (Insufficient Space on Resource) - The resource does not have
          sufficient space to record the state of the resource after the
          execution of this method.
          
          
          3.10.6    Examples
          
          
          3.10.6.1  HTML file modification
          
          The following example shows a modification of the title and
          contents of the HTML resource http://www.example.org/hello.html.
          
          
          
          
          
          
          Before:
               <HTML>
               <HEAD>
               <TITLE>Hello world HTML page</TITLE>
               </HEAD>
               <BODY>
               <P>Hello, world!</P>
               </BODY>
               </HTML>
          PATCH Request:                     Response:
               PATCH hello.html HTTP/1.1
               Host: www.example.org
               Content-Type: text/xml
               Content-Length: xxx
          
                                             HTTP/1.1 100 Continue
               <?XML:Namespace href =
               Shttp://www.ietf.org/standards/dav/patch/" AS = "D"/>
               <D:ResourceUpdate>
                    <Replace XML-SPACE = "PRESERVE"><octet-range>14</octet-
               range>&003CTITLE&003ENew Title&003C/TITLE&003E</Replace>
                    <Delete><octet-range>38-50</Delete>
               <Insert XML-SPACE = "PRESERVE"><octet-range>86</>&
               003CP&003ENew paragraph&003C/P&003E</Insert>
               </D:ResourceUpdate>
                                             HTTP/1.1 200 OK
          After:
               <HTML>
               <HEAD>
               <TITLE>New Title</TITLE>
               </HEAD>
               <BODY>
               <P>Hello, world!</P>
               <P>New paragraph</P>
               </BODY>
               </HTML>
          
          
          3.11 Headers
          
          
          3.11.1    Destination Header
          
          The Destination header specifies a destination resource for
          methods such as COPY and MOVE, which take two URIs as parameters.
               Destination= "Destination" ":" URI
          
          
          3.11.2    Enforce-Live-Properties Header
          
          The Enforce-Live-Properties header specifies properties that MUST
          be "live" after they are copied (moved) to the destination
          resource of a copy (or move). If the value "*" is given for the
          header, then it designates all live properties on the source
          resource.  If the value is "Omit" then the server MUST NOT
          duplicate on the destination resource any properties that are
          defined on the source resource. If this header is not included
          then the server is expected to act as defined by the default
          property handling behavior of the associated method.
          
               EnforceLiveProperties = "Enforce-Live-Properties" ":" ("*" |
               "Omit" | 1#(Property-Name))
               Property-Name = "<" URI ">"
          
          
          
          
          
          
          3.11.3    Overwrite Header
          
          The Overwrite header specifies whether the server should
          overwrite the state of a non-null destination resource during a
          COPY or MOVE.  A value of "false" states that the server MUST NOT
          perform the COPY or MOVE operation if the state of the
          destination resource is non-null. By default, the value of
          Overwrite is "true," and a client MAY omit this header from a
          request when its value is "true." While the Overwrite header
          appears to duplicate the functionality of the If-Match: * header
          of HTTP/1.1, If-Match applies only to the Request-URI, and not to
          the Destination of a COPY or MOVE.
          
               Overwrite = "Overwrite" ":" ("true" | "false")
          
          If there is a conflict and the Overwrite header equals "true", or
          is absent and thus defaults to "true", then the method MUST fail
          with a 409 Conflict.
          
          
          3.11.4    Destroy Header
          
          When deleting a resource the client often wishes to specify
          exactly what sort of delete is being enacted. The Destroy header,
          used with the Mandatory header, allows the client to specify the
          end result they desire. The Destroy header is specified as
          follows:
          
          The Undelete token requests that, if possible, the resource
          should be left in a state such that it can be undeleted. The
          server is not required to honor this request.
          
          The NoUndelete token requests that the resource MUST NOT be left
          in a state such that it can be undeleted.
          
          The VersionDestroy token includes the functionality of the
          NoUndelete token and extends it to include having the server
          remove all versioning references to the resource that it has
          control over.
          
               DestroyHeader = "Destroy" ":" #Choices
          
          Choices = "VersionDestroy" | "NoUndelete" | "Undelete" | token
          |"<" URI ">" ; a token extension MUST NOT be used unless it is
          specified in a RFC16, otherwise a URI MUST be used for
          extensions.
          
          
          3.11.5    Collection-Member Header
          
          The Collection-Member header specifies the URI of an external
          resource to be added/deleted to/from a collection.
          
               CollectionMember = "Collection-Member" ":" URI
          
          
          3.12 Links
          
          
          3.12.1    Source Link Property Type
          
          Name:     http://www.ietf.org/standards/dav/link/source
          Purpose:       The destination of the source link identifies the
          resource that contains the unprocessed source of the link’s
          source.
          
          
          
          
          
          
          Schema:        http://www.ietf.org/standards/dav/link/
          Parent:        Any
          Value:         An XML document with zero or more link XML
          elements.
          
          Discussion: The source of the link (src) is typically the URI of
          the output resource on which the link is defined, and there is
          typically only one destination (dst) of the link, which is the
          URI where the unprocessed source of the resource may be accessed.
          When more than one link destination exists, this specification
          asserts no policy on ordering.
          
          
          4    State Tokens
          
          4.1  Overview
          
          
          4.1.1     Problem Description
          
          There are times when a principal will want to predicate
          successful execution of a method on the current state of a
          resource.  While HTTP/1.1 provides a mechanism for conditional
          execution of methods using entity tags via the "If-Match" and
          "If-None-Match" headers, the mechanism is not sufficiently
          extensibleto express conditional statements involving more
          generic state indicators, such as lock tokens.
          
          The fundamental issue with entity tags is that they can only be
          generated by a resource. However there are times when a client
          will want to be able to share state tokens between resources,
          potentially on different servers, as well as be able to generate
          certain types of lock tokens without first having to communicate
          with a server.
          
          For example, a principal may wish to require that resource B have
          a certain state in order for a method to successfully execute on
          resource A. If the client submits an e-tag from resource B to
          resource A, then A has no way of knowing that the e-tag is meant
          to describe resource B.
          
          Another example occurs when a principal wishes to predicate the
          successful completion of a method on the absence of any locks on
          a resource. It is not sufficient to submit an "If-None-Match: *"
          as this refers to the existence of an entity, not of a lock.
          
          This draft defines the term "state token" as an identifier for a
          state of a resource. The sections below define requirements for
          state tokens and provide a  state token syntax, along with two
          new headers which can accept the new state token syntax.
          
          
          4.1.2     Solution Requirements
          
          
          4.1.2.1   Syntax
          
          Self-Describing. A state token must be self describing such that
          upon inspecting a state token it is possible to determine what
          sort of state token it is, what resource(s) it applies to, and
          what state it represents.
          
          This self-describing nature allows servers to accept tokens from
          other servers and potentially be able to coordinate state
          
          
          
          
          
          
          information cross resource and cross site through standardized
          protocols. For example, the execution of a request on resource A
          can be predicated on the state of resource B, where A and B are
          potentially on different servers.
          
          Client Generable. The state token syntax must allow, when
          appropriate, for clients to generate a state token without having
          first communicated with a server.
          
          One drawback of entity tags is that they are set by the server,
          and there is no interoperable algorithm for calculating an entity
          tag. Consequently, a client cannot generate an entity tag from a
          particular state of a resource.  However, a state token which
          encodes an MD5 state hash could be calculated by a client based
          on a client-held state of a resource, and then submitted to a
          server in a conditional method invocation.
          
          Another potential use for client generable state tokens is for a
          client to generate lock tokens with wild card fields, and hence
          be able to express conditionals such as: "only execute this GET
          if there are no write locks on this resource."
          
          
          4.1.2.2   Conditonals
          
          Universal. A solution must be applicable to all requests.
          Positive and Negative. Conditional expressions must allow for the
          expression of both positive and negative state requirements.
          
          
          4.2  State Token Syntax
          State tokens are URLs employing the following syntax:
          State-Token = "StateToken:" Type ":" Resources ":" State-Info
          Type = "Type" "=" Caret-encoded-URL
          Resources = "Res" "=" Caret-encoded-URL
          Caret-encoded-URL = "^" Resource "^"
          Resource = <A URI where all "^" characters are escaped>
          State-Info = *(uchar | reserved)  ; uchar, reserved defined
          section 3.2.1 of RFC 2068
          
          This proposal has created a new URL scheme for state tokens
          because a state token names a network resource using its normal
          name, which is typically state-invariant, along with additional
          information that specifies a particular state of the resource.
          Encoding the state information into the native URL scheme of the
          network resource was not felt to be safe, since freedom from name
          space collisions could not be guaranteed. If this proposal is
          accepted, the StateToken URL scheme will need to be defined and
          registered with IANA.
          
          State Token URLs begin with the URL scheme name "StateToken"
          rather than the name of the particular state token type they
          represent in order to make the URL self describing. Thus it is
          possible to examine the URL and know, at a minimum, that it is a
          state token.
          
          Labeled name/value pairs are used within the token to allow new
          fields to be added. Processors of state tokens MUST be prepared
          to accept the fields in whatever order they are present and MUST
          ignore any fields they do not understand.
          The "Type" field specifies the type of the state information
          encoded in the state token. A URL is used in order to avoid
          namespace collisions.
          
          The "Res" field identifies the resource for which the state token
          
          
          
          
          
          
          specifies a particular state. Since commas and spaces are
          acceptable URL characters, a caret is used to delimit a URL.
          Since a caret is an acceptable URL character, any instances of it
          must be escaped using the % escape convention.
          
          The State-Info production is expanded upon in descriptions of
          specific state token types, and is intended to contain the state
          description information for a particular state token.
          
          
          4.3  State Token Conditional Headers
          
          
          4.3.1     If-State-Match
          
          If-State-Match = "If-State-Match" ":" ("AND" | "OR") 1#("<"
          State-Token ">")
          
          The If-State-Match header is intended to have similar
          functionality to the If-Match header defined in section 14.25 of
          RFC 2068.
          
          If the AND keyword is used and all of the state tokens identify
          the state of the resource, then the server MAY perform the
          requested method. If the OR keyword is used and any of the state
          tokens identifies the current state of the resource, then server
          MAY perform the requested method.  If neither of the keyword
          requirements is met, the server MUST NOT perform the requested
          method, and MUST return a 412 (Precondition Failed) response.
          
          
          4.3.2     If-None-State-Match
          
          If-None-State-Match = "If-None-State-Match" ":" 1#("<" State-
          Token ">")
          
          The If-None-State-Match header is intended to have similar
          functionality to the If-None-Match header defined in section
          14.26 of RFC 2068.
          
          If any of the state tokens identifies the current state of the
          resource, the server MUST NOT perform the requested method.
          Instead, if the request method was GET, HEAD, INDEX, or GETMETA,
          the server SHOULD respond with a 304 (Not Modified) response,
          including the cache-related entity-header fields (particularly
          ETag) of the current state of the resource.  For all other
          request methods, the server MUST respond with a status of 412
          (Precondition Failed).
          
          If none of the state tokens identifies the current state of the
          resource, the server MAY perform the requested method.
          
          Note that the "AND" and "OR" keywords specified with the If-
          State-Match header are intentionally not defined for If-None-
          State-Match, because this functionality is not required.
          
          
          4.4  State Token Header
          
          State-Token-Header = "State-Token" ":" 1#("<" State-Token ">")
          The State Token header is intended to have similar functionality
          to the etag header defined in section 14.20 of RFC 2068. The
          purpose of the tag is to return state tokens defined on a
          
          
          
          
          
          
          resource in a response. The contents of the state-token are not
          guaranteed to be exhaustive and are generally used to return a
          new state token that has been defined as the result of a method.
          For example, if a LOCK method were successfully executed on a
          resource the response would include a state token header with the
          lock state token included.
          
          
          4.5  E-Tags
          E-tags have already been deployed using the If-Match and If-None-
          Match headers.  Introducing two mechanisms to express e-tags
          would only confuse matters, therefore e-tags should continue to
          be expressed using quoted strings and the If-Match and If-None-
          Match headers.
          
          
          5    Locking
          
          5.1  Locking: Introduction
          
          Locking is used to arbitrate access to a resource amongst
          principals that have equal access rights to that resource.
          
          This specification allows locks to vary over two parameters, the
          number of principals involved and the type of access to be
          granted. Furthermore, this document only provides the definition
          of locking for one access type, write. However, the syntax is
          extensible, and allows the specification of other access types.
          
          
          5.1.1     Exclusive Vs. Shared Locks
          
          The most basic form of lock is an exclusive lock. This is a lock
          where the access right in question is only granted to a single
          principal. The need for this arbitration results from a desire to
          avoid having to constantly merge results. In fact, many users so
          dislike having to merge that they would rather serialize their
          access to a resource rather than have to constantly perform
          merges.
          
          However, there are times when the goal of a lock is not to
          exclude others from exercising an access right but rather to
          provide a mechanism for principals to indicate that they intend
          to exercise their access right.  Shared locks are provided for
          this case. A shared lock allows multiple principals to receive a
          lock, hence any principal with appropriate access can get the
          lock.
          
          With shared locks there are two trust sets that affect a
          resource.  The first trust set is created by access permissions.
          Principals who are trusted, for example, may have permission to
          write the resource, those who are not, don't.  Among those who
          have access permission to write the resource, the set of
          principals who have taken out a shared lock also must trust each
          other, creating a (typically) smaller trust set within the access
          permission write set.
          
          Starting with every possible principal on the Internet, in most
          situations the vast majority of these principals will not have
          write access to a given resource.  Of the small number who do
          have write access, some principals may decide to guarantee their
          edits are free from overwrite conflicts by using exclusive write
          locks. Others may decide they trust their collaborators (the
          potential set of collaborators being the set of principals who
          have write permission) and use a shared lock, which informs their
          
          
          
          
          
          
          collaborators that a principal is potentially working on the
          resource.
          
          The WebDAV extensions to HTTP do not need to provide all of the
          communications paths necessary for principals to coordinate their
          activities.  When using shared locks, principals may use any out
          of band communication channel to coordinate their work (e.g.,
          face-to-face interaction, written notes, post-it notes on the
          screen, telephone conversation, email, etc.)  The intent of a
          shared lock is to let collaborators know who else is potentially
          working on a resource.
          
          Shared locks are included because experience from web distributed
          authoring systems has indicated that exclusive write locks are
          often too rigid.  An exclusive write lock is used to enforce a
          particular editing process: take out exclusive write lock, read
          the resource, perform edits, write the resource, release the
          lock.  What happens if the lock isn't released?  While the time-
          out mechanism provides one solution, if you need to force the
          release of a lock immediately, it doesn't help much.  Granted, an
          administrator can release the lock for you, but this could become
          a significant burden for large sites. In addition there is the
          problem that an administrator may not be immediately available.
          
          Despite their potential problems, exclusive write locks are
          extremely useful, since often a guarantee of freedom from
          overwrite conflicts is what is needed.  The tradeoff described in
          this specification is to provide exclusive write locks, but also
          to provide a less strict mechanism in the form of shared locks
          which can be used by a set of people who trust each other and who
          have access to a communications channel external to HTTP which
          can be used to negotiate writing to the resource.
          
          
          5.1.2     Required Support
          
          A WebDAV compliant server is not required to support locking in
          any form. If the server does support locking it may choose to
          support any combination of exclusive and shared locks for any
          access types.
          
          The reason for this flexibility is that server implementers have
          said that they are willing to accept minimum requirements on all
          services but locking. Locking policy strikes to the very heart of
          their resource management and versioning systems and they require
          control over what sort of locking will be made available. For
          example, some systems only support shared write locks while
          others only provide support for exclusive write locks while yet
          others use no locking at all. As each system is sufficiently
          different to merit exclusion of certain locking features, the
          authors are proposing that locking be allowed as the sole axis of
          negotiation within WebDAV.
          
          
          5.2  LOCK Method
          
          The following sections describe the LOCK method, which is used to
          take out a lock of any access type.  These sections on the LOCK
          method describe only those semantics that are specific to the
          LOCK method and are independent of the access type of the lock
          being requested.  Once the general LOCK method has been
          described, subsequent sections describe the semantics of the
          "write" access type, and the write lock.
          
          
          5.2.1     Operation
          
          
          
          
          
          
          
          A LOCK method invocation creates the lock specified by the Lock-
          Info header on the Request-URI. Lock method requests SHOULD NOT
          have a request body. A user-agent SHOULD submit an Owner header
          field with a lock request.
          
          A successful response to a lock invocation MUST include Lock-
          Token and Time-Out headers.
          
          
          5.2.2     The Effect of Locks on Properties and Containers
          
          By default the scope of a lock is the entire state of the
          resource, including its body and associated properties. As a
          result, a lock on a resource also locks the resource's
          properties, and a lock on a property may lock a property's
          resource or may restrict the ability to lock the property's
          resource. Only a single lock token MUST be used when a lock
          extends to cover both a resource and its properties. Note that
          certain lock types MAY override this behavior.
          
          For containers, a lock also affects the ability to add or remove
          members. The nature of the effect depends upon the type of access
          control involved.
          
          
          5.2.3     Locking Replicated Resources
          
          Some servers automatically replicate resources across multiple
          URLs. In such a circumstance the server MAY only accept a lock on
          one of the URLs if the server can guarantee that the lock will be
          honored across all the URLs.
          
          
          5.2.4     Locking Multiple Resources
          
          The LOCK method supports locking multiple resources
          simultaneously by allowing for the listing of several URIs in the
          LOCK request. These URIs, in addition to the Request-URI, are
          then to be locked as a result of the LOCK method's invocation.
          When multiple resources are specified the LOCK method only
          succeeds if all specified resources are successfully locked.
          
          The Lock-Tree option of the lock request specifies that the
          resource and all its internal children (including internal
          collections, and their internal members) are to be locked. This
          is another mechanism by which a request for a lock on multiple
          resources can be specified.
          
          Currently existing locks can not be extended to cover more or
          less resources, and any request to expand or contract the number
          of resources in a lock MUST fail with a 409 Conflict status code.
          So, for example, if resource A is exclusively write locked and
          then the same principal asked to exclusively write lock resources
          A, B, and C, the request would fail as A is already locked and
          the lock can not be extended.
          
          A successful result will return a single lock token which
          represents all the resources that have been locked. If an UNLOCK
          is executed on this token, all associated resources are unlocked.
          
          If the lock can not be granted to all resources, a 406 Conflict
          status code MUST be returned with a response entity body
          containing a multiresponse XML element describing which
          resource(s) prevented the lock from being granted.
          
          
          
          
          
          
          
          
          5.2.5     Interaction with other Methods
          
          The interaction of a LOCK with various methods is dependent upon
          the lock type. However, independent of lock type, a successful
          DELETE of a resource MUST cause all of its locks to be removed.
          
          
          5.2.6     Lock Compatibility Table
          
          The table below describes the behavior that occurs when a lock
          request is made on a resource.
          
          Current lock state/      Shared Lock       Exclusive Lock
          Lock request
          None                     True              True
          Shared Lock              True              False
          Exclusive Lock           False             False*
          
          Legend: True = lock MAY be granted.  False = lock MUST NOT be
          granted.  *=if the principal requesting the lock is the owner of
          the lock, the lock MAY be regranted.
          
          The current lock state of a resource is given in the leftmost
          column, and lock requests are listed in the first row.  The
          intersection of a row and column gives the result of a lock
          request.  For example, if a shared lock is held on a resource,
          and an exclusive lock is requested, the table entry is "false",
          indicating the lock must not be granted.
          
          If an exclusive or shared lock is re-requested by the principal
          who owns the lock, the lock MUST be regranted. If the lock is
          regranted, the same lock token that was previously issued MUST be
          returned.
          
          
          5.2.7     Status Codes
          
          409 "Conflict" - The resource is locked, so the method has been
          rejected.
          
          412 "Precondition Failed" - The included state-token was not
          enforceable on this resource or the request in the lock-info
          header could not be satisfied by the server.
          
          
          5.2.8     Lock-Info Request Header
          
          The Lock-Info request header specifies the scope and type of a
          lock for a LOCK method request. The syntax specification below is
          extensible, allowing new type and scope identifiers to be added.
          
          LockInfo = "Lock-Info" ":" DAVLockType SP DAVLockScope [SP
          AdditionalLocks] [SP Lock-Tree]
          DAVLockType = "LockType" "=" DAVLockTypeValue
          DAVLockTypeValue = ("Write" | *(uchar | reserved))
          DAVLockScope = "LockScope" "=" DAVLockScopeValue
          DAVLockScopeValue = ("Exclusive" |"Shared" | *(uchar | reserved))
          AdditionalLocks = "AddLocks" "=" 1*("<" URI ">")
          Lock-Tree = "Lock-Tree" "=" ("True" | "False")
          
          The LockType field specifies the access type of the lock.  At
          present, this specification only defines one lock type, the
          "Write" lock.  The LockScope field specifies whether the lock is
          
          
          
          
          
          
          an exclusive lock, or a shared lock.  The AddLocks field
          specifies additional URIs, beyond the Request-URI, to which the
          lock request applies.  The LockTree field is used to specify
          recursive locks.  If the LockTree field is "true", the lock
          request applies to the hierarchy traversal of the internal
          members resources of the Request-URI, and the AddLocks URIs,
          inclusive of the Request-URI and the AddLocks URIs. It is not an
          error if LockTree is true, and the Request-URI or the AddLocks
          URIs have no internal member resources. By default, the value of
          LockTree is "false", and this field MAY be omitted when its value
          is false.
          
          
          5.2.9     Owner Request Header
          
          
          5.2.9.1   Problem Description
          
          When discovering the list of owners of locks on a resource, a
          principal may want to be able to contact the owner directly. For
          this to be possible the lock discovery mechanism must provide
          enough information for the lock owner to be contacted.
          Additionally, programs may wish to be able to record structured
          information in the owner header so that other programs may be
          able to parse it later. Note, however, that these programs may
          not necessarily be coordinating so there need be no guarantee
          that the information can be parsed.
          
          
          5.2.9.2   Solution Requirements
          
          Not all systems have authentication procedures that provide
          sufficient information to identify a particular user in a way
          that is meaningful to a person. In addition, many systems that do
          have sufficient information, such as a name and e-mail address,
          do not have the ability to associate this information with the
          lock discovery mechanism. Therefore a means is needed to allow
          principals to provide authentication in a manner which will be
          meaningful to a person.
          
          The From header (defined in RFC 2068), which contains only an
          email mailbox, is not sufficient for the purposes of quick
          identification. When desperately looking for someone to remove a
          lock, e-mail is often not sufficient. A telephone number (cell
          number, pager number, etc.) would be better. Furthermore, the
          email address in the From header only optionally includes the
          owners name and that name is often set to an alias anyway.
          Therefore a header more flexible than From is required.
          
          The value also needs to be such that both man and machine can
          place values in it and later retrieve those values.
          
          
          5.2.9.3   Syntax
          
          Owner = "Owner" ":" (Coded-XML  | quoted-string)
          Coded-XML = field-content    ; XML where any character which is
          not legal in field-content (see section 4.2 of [Fielding et al.,
          1997]) is XML encoded
          
          The XML SHOULD provide information sufficient for either directly
          contacting the principal (such as a telephone number or e-mail
          URI), or for discovering the principal (such as the URL of a
          homepage) who owns the lock. The quoted string SHOULD provide a
          means for directly contacting the principal who owns the lock,
          
          
          
          
          
          
          such as a name and telephone number.
          
          
          5.2.10    Time-Out Header
          
          
          5.2.10.1  Problem Description
          
          In a perfect world principals take out locks, work on the
          resource, and then remove the lock when it is no longer needed.
          However, this process is frequently not completed, leaving active
          but unused locks. Reasons for this include client programs
          crashing and losing information about locks, users leaving their
          systems for the day and forgetting to remove their locks, etc. As
          a result of this behavior, servers need to establish a policy by
          which they can remove a lock without input from the lock owner.
          Once such a policy is instituted, the server also needs a
          mechanism to inform the principal of the policy.
          
          
          5.2.10.2  Solution Requirements
          
          There are two basic lock removal policies: administrator and time
          based removal. In the case of administrator based removal, a
          principal other than the lock owner has sufficient access rights
          to order the lock removed, even though they did not take it out.
          The second policy type is time based removal.  In this case, a
          timer is set as soon as the lock is created. Every time a method
          is executed on any resource covered by the lock, the timer is
          reset. If the timer runs out, the lock is removed.
          
          User-agents MUST assume that locks may arbitrarily disappear at
          any time. If their actions require confirmation of the existence
          of a lock then the If-State headers are available.
          
          
          5.2.10.3  Syntax
          
          TimeOut = "Time-Out" ":" 1#TimeType
          TimeType = ("Second-" DAVTimeOutVal | "Infinite" | Extend)
          DAVTimeOutVal = 1*digit
          Extend = RFC-Reg | URL "-" Token ; The URL format is used for
          unregistered TimeTypes
          RFC-Req = Token ; This is a TimeType that has been published as
          an RFC
          
          
          Clients MAY include TimeOut headers in their LOCK requests.
          However the server is not required to honor or even consider the
          request. Clients MUST NOT submit a Time-Out request header with
          any method other than a LOCK method.
          
          A Time-Out request header MUST contain at least one TimeType and
          MAY contain multiple TimeType entries. The purpose of listing
          multiple TimeType is to indicate multiple different values and
          value types that are acceptable to the client. The client lists
          the TimeType entries in order of preference.
          
          The Time-Out response header MUST use a Second value, Infinite,
          or a TimeType the client has indicated familiarity with. The
          server MAY assume a client is familiar with any TimeType
          submitted in a Time-Out header.
          
          The "Second" TimeType specifies the number of seconds that MUST
          elapse between granting of the lock at the server, and the
          
          
          
          
          
          
          automatic removal of the lock. A server MUST not generate a time
          out value for "Second" greater than 2^32-1.
          
          The time out counter is restarted any time the client sends a
          method to any member of the lock, including unsupported methods,
          or methods which are unsuccessful. It is recommended that the
          HEAD method be used when the goal is simply to restart the time
          out counter.
          
          If the timeout expires then the lock is lost. Specifically the
          server SHOULD act as if an UNLOCK method was executed by the
          server on the resource using the lock token of the timed-out
          lock, performed with its override authority. Thus logs,
          notifications, and other mechanisms that act as side effects to
          the granting and removal of a lock will be properly informed as
          to the disposition of the lock.
          
          Servers are advised to pay close attention to the values
          submitted by clients, as they will be indicative of the type of
          activity the client intends to perform. For example, an applet
          running in a browser may need to lock a resource, but because of
          the instability of the environment within which the applet is
          running, the applet may be turned off without warning. As a
          result, the applet is likely to ask for a relatively small time-
          out value so that if the applet dies, the lock can be quickly
          harvested. However a document management system is likely to ask
          for an extremely long time-out because its user may be planning
          on going off-line.
          
          
          5.2.11    Lock Response
          
          A successful lock response MUST contain a Lock-Token response
          header, a Time-Out header and a PROP element in the response body
          which contains the value of the LockDiscovery property.
          
          
          5.2.11.1  Lock-Token Response Header
          
          If a resource is successfully locked then a lock-token header
          will be returned containing the lock token that represents the
          lock.
          
          Lock-Token = "Lock-Token" ":" URI
          
          
          5.2.12    Example - Simple Lock Request
          
          LOCK /workspace/webdav/proposal.doc HTTP/1.1
          Host: webdav.sb.aol.com
          Lock-Info: LockType=Write LockScope=Exclusive
          Time-Out: Infinite; Second-4100000000
          Owner: <?XML:Namespace href="http://www.ietf.org/standards/dav/"
          AS =
          "D"/><D:HREF>http://www.ics.uci.edu/~ejw/contact.html</D:HREF>
          
          
          HTTP/1.1 200 OK
          Lock-Token: OpaqueLockToken:xyz122393481230912asdfa09s8df09s7df08
          sd0f98a098sda
          Time-Out: Second-604800
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
          
          
          
          
          
          
               href ="http://www.ietf.org/standards/dav/" AS = "D"/>
          <D:Prop>
               <lockdiscovery>
                    <activelock>
                         <locktype>write</locktype>
                         <lockscope>exclusive</lockscope>
                         <addlocks/>
                         <owner>
               <HREF>http://www.ics.uci.edu/~ejw/contact.html</HREF>
                         </owner>
                         <timeout>Second-604800</timeout>
                         <locktoken>
                              <HREF>
                         OpaqueLockToken:xyz122393481230912asdfa09s8df09s7d
                         f08sd0f98a098sda
                              </HREF>
                         </locktoken>
                    </activelock>
               </lockdiscovery>
          </D:Prop>
          
          This example shows the successful creation of an exclusive write
          lock on resource
          http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The
          resource http://www.ics.uci.edu/~ejw/contact.html contains
          contact information for the owner of the lock. The server has an
          activity-based timeout policy in place on this resource, which
          causes the lock to automatically be removed after 1 week (604800
          seconds). The response has a Lock-Token header that gives the
          state token URL for the lock token generated by this lock
          request.
          
          
          5.2.13    Example - Multi-Resource Lock Request
          
          LOCK /workspace/webdav/proposal.doc HTTP/1.1
          Host: webdav.sb.aol.com
          Lock-Info: LockType=Write LockScope=Exclusive
          Addlocks=<http://webdav.sb.aol.com/workspace/><http://foo.bar/bla
          h>
          Time-Out: Infinite, Second-4100000000
          Owner: <http://www.ics.uci.edu/~ejw/contact.html>
          
          
          HTTP/1.1 409 Conflict
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" As = "D"/>
          <D:MultiResponse>
               <Response>
                    <HREF>
                    http://webdav.sb.aol.com/workspace/webdav/proposal.doc
                    </HREF>
                    <HREF>
                    http://webdav.sb.aol.com/workspace/webdav/
                    </HREF>
                    <Status>HTTP/1.1 202 Accepted</Status>
               </Response>
               <Response>
                    <HREF>http://foo.bar/blah</HREF>
                    <Status>HTTP/1.1 403 Forbidden</Status>
               </Response>
          </D:MultiResponse>
          
          
          
          
          
          
          
          This example shows a request for an exclusive write lock on three
          resources,
          http://webdav.sb.aol.com/workspace/webdav/proposal.doc,
          http://webdav.sb.aol.com/workspace/, and http://foo.bar/blah.  In
          this request, the client has specified that it desires an
          infinite length lock, if available, otherwise a timeout of 4.1
          billion seconds, if available.  The Owner header field specifies
          the web address for contact information for the principal taking
          out the lock.
          
          This lock request has failed, because the server rejected the
          lock request for http://foo.bar/blah.  The 409 Conflict status
          code indicates that the server was unable to satisfy the request
          because there is a conflict between the state of the resources
          and the operation named in the request.  Within the
          multiresponse, the 202 Accepted status code indicates that the
          lock method was accepted by the resources, and would have been
          completed if all resources named in the request were able to be
          locked.  The 403 Forbidden status code indicates that the server
          does not allow lock requests on this resource.
          
          
          5.3  Write Lock
          
          This section describes the semantics specific to the write access
          type for locks.  The write lock is a specific instance of a lock
          type, and is the only lock type described in this specification.
          
          
          5.3.1     Methods Restricted by Write Locks
          
          A write lock prevents a principal without the lock from
          successfully executing a PUT, POST, PATCH, PROPPATCH, MOVE,
          DELETE, MKCOL, ADDREF or DELREF on the locked resource. All other
          current methods, GET in particular, function independent of the
          lock.
          
          Note, however, that as new methods are created it will be
          necessary to specify how they interact with a write lock.
          
          
          5.3.2     Write Locks and Properties
          
          While those without a write lock may not alter a property on a
          resource it is still possible for the values of live properties
          to change, even while locked, due to the requirements of their
          schemas. Only dead properties and live properties defined to
          respect locks are guaranteed to not change while write locked.
          
          If a property is write locked then a LOCK request on the
          associated resource MUST fail with a 409 "Conflict". Note that a
          write lock on a property MAY be extended to include the
          associated resource without the principal having explicitly
          requested the extension.
          
          
          5.3.3     Write Locks and Null Resources
          
          It is possible to assert a write lock on a null resource in order
          to lock the name. Please note, however, that locking a null
          resource effectively makes the resource non-null as the resource
          now has lock related properties defined on it.
          
          
          5.3.4     Write Locks and Collections
          
          
          
          
          
          
          
          A write lock on a collection prevents the addition or removal of
          members of the collection. As a consequence, when a principal
          issues a request to create a new internal member of a collection
          using PUT or POST, or to remove an existing internal member of a
          collection using DELETE, this request MUST fail if the principal
          does not have a write lock on the collection.
          
          However, if a write lock request is issued to a collection
          containing internal member resources that are currently locked,
          the request MUST fail with a 409 Conflict status code.
          
          
          5.3.5     Write Locks and COPY/MOVE
          
          The owner of a write lock MUST NOT execute a MOVE method on a
          resource they have locked. This specification intentionally does
          not define what happens if a MOVE method request is made on a
          locked resource by the lock's owner.
          
          A COPY method invocation MUST NOT duplicate any write locks
          active on the source.
          
          
          5.3.6     Re-issuing Write Locks
          
          If a principal already owns a write lock on a resource, any
          future requests for the same type of write lock, on the same
          resource, while the principal's previous write lock is in effect,
          MUST result in a successful response with the same lock token as
          provided for the currently existing lock. Two lock requests are
          defined to be identical if their Lock-Info headers are identical.
          
          
          5.3.7     Write Locks and The State-Token Header
          
          
          5.3.7.1   Problem Definition
          
          If a user agent is not required to have knowledge about a lock
          when requesting an operation on a locked resource, the following
          scenario might occur. Program A, run by User A, takes out a write
          lock on a resource. Program B, also run by User A, has no
          knowledge of the lock taken out by Program A, yet performs a PUT
          to the locked resource. In this scenario, the PUT succeeds
          because locks are associated with a principal, not a program, and
          thus program B, because it is acting with principal A’s
          credential, is allowed to perform the PUT. However, had program B
          known about the lock, it would not have overwritten the resource,
          preferring instead to present a dialog box describing the
          conflict to the user. Due to this scenario, a mechanism is needed
          to prevent different programs from accidentally ignoring locks
          taken out by other programs with the same authorization.
          
          
          5.3.7.2   Solution Requirement
          
          The solution must not require principals to perform discovery in
          order to prevent accidental overwrites as this could cause race
          conditions.
          
          The solution must not require that clients guess what sorts of
          locks might be used and use if-state-match headers with wildcards
          to prevent collisions. The problem with trying to "guess" which
          locks are being used is that new lock types might be introduced,
          
          
          
          
          
          
          and the program would not know to "guess them". So, for example,
          a client might put in an if-state-match header with a wildcard
          specifying that if any write lock is outstanding then the
          operation should fail. However a new read/write lock could be
          introduced which the client would not know to put in the header.
          
          
          5.3.7.3   State-Token Header
          
          The State-Token header, containing a lock token owned by the
          requesting principal, is used by the principal to indicate that
          the principal is aware of the existence of the lock specified by
          the lock token. It is used in the following way.
          
          If the following conditions are met:
               1.   a user-agent has authenticated itself as a principal,
               2.   the user-agent is submitting a method request to a
          resource
                    on which the principal owns a write lock,
               3.   the method is restricted by a write lock, as defined in
          the
                    section "Methods Restricted by a Write Lock",
          then the method request MUST include a State-Token header with
          the  lock token of the write lock, or the method fails with a 409
          Conflict status code. If multiple resources are involved with a
          method, such as a COPY or MOVE method, then the lock tokens, if
          any, for all involved resources, MUST be included in the State-
          Token request header.
          
          For example, Program A, used by user A, takes out a write lock on
          a resource. Program A then makes a number of PUT requests on the
          locked resource, all the requests contain a State-Token header
          which includes the write lock state token. Program B, also run by
          User A, then proceeds to perform a PUT to the locked resource.
          However program B was not aware of the existence of the lock and
          so does not include the appropriate state-token header. The
          method is rejected even though principal A is authorized to
          perform the PUT. Program B can, if it so chooses, now perform
          lock discovery and obtain the lock token. Note that program A and
          B can perform GETs without using the state-token header because
          the ability to perform a GET is not affected by a write lock.
          
          Having a lock state token provides no special access rights.
          Anyone can find out anyone else’s lock state token by performing
          lock discovery. Locks are to be enforced based upon whatever
          authentication mechanism is used by the server, not based on the
          secrecy of the token values.
          
          
          5.3.7.3.1 Example
          
          COPY /~fielding/index.html HTTP/1.1
          Host: www.ics.uci.edu
          Destination: http://www.ics.uci.edu/users/f/fielding/index.html
          State-Token: <OpaqueLockToken:123AbcEfg1284h23h2>
          <OpaqueLockToken:AAAASDFcalkjfdas12312>
          
          
          HTTP/1.1 200 OK
          
          In this example, both the source and destination are locked so
          two lock tokens must be submitted. If only one of the two
          resources was locked, then only one token would have to be
          submitted.
          
          
          
          
          
          
          
          5.4  Lock Tokens
          
          
          5.4.1     Problem Description
          
          It is possible that once a lock has been granted it may be
          removed without the lock owner’s knowledge. This can cause
          serialization problems if the lock owner executes methods
          thinking their lock is still active. Due to this, a mechanism is
          needed for a principal to predicate the successful execution of a
          message upon the continuing existence of a lock.
          
          
          5.4.2     Lock Token Introduction
          
          A lock token is a type of state token that describes a particular
          lock.  A lock token is returned by every successful LOCK
          operation, and can also be discovered through lock discovery on a
          resource.
          
          There are two types of lock tokens, a generic lock token, which
          is unique only for a particular resource, and an opaque lock
          token, which is unique across all resources for all time.
          
          Uniqueness for a particular resource prevents problems with long
          held outstanding lock tokens being confused with newer tokens.
          This uniqueness requirement is the same as for e-tags. Uniqueness
          across all resources for all time allows for tokens to be
          submitted across resources and servers without fear of confusion.
          
          Generic lock tokens, because of their relaxed uniqueness
          requirements, are faster to generate than opaque lock tokens.
          
          
          5.4.3     Generic Lock Tokens
          
          Any valid URI can be used by the resource as a generic lock
          token. The only requirement is that the lock token MUST never
          have been issued previously on that resource. Because a lock
          token is only guaranteed to be unique on the resource that
          generated it, the lock token MUST NOT be submitted in a state-
          token request header or an if-state[-not]-match header on any
          resource but the resource that generated it.
          
          
          5.4.4     OpaqueLockToken Lock Token
          
          The opaquelocktoken scheme is designed to be unique across all
          resources for all time. Due to this uniqueness quality, a client
          MAY submit an opaque lock token in a state-token request header
          and an if-state[-not]-match header on a resource other than the
          one that returned it.
          
          All resources MUST recognize the opaquelocktoken scheme and be
          able to, at minimum, recognize that the lock token was not
          generated by the resource. Note, however, that resources are not
          required to generate opaquelocktokens.
          
          In order to guarantee uniqueness across all resources for all
          time the opaquelocktoken requires the use of the GUID mechanism.
          
          Opaquelocktoken generators however have a choice of how they
          create these tokens. They can either generate a new GUID for
          every lock token they create, which is potentially very
          
          
          
          
          
          
          expensive, or they can create a single GUID and then add
          extension characters. If the second method is selected then the
          program generating the extensions MUST guarantee that the same
          extension will never be used twice with the associated GUID.
          
          Opaque-Lock-Token = "OpaqueLockToken" ":" GUID [Extension]
          GUID = ; As defined in [LEACH]
          Extension = *urlc   ;urlc is defined in [Berners-Lee et al.,
          1997] (draft-fielding-url-syntax-07.txt)
          
          
          
          5.5  UNLOCK Method
          
          
          5.5.1     Problem Definition
          
          The UNLOCK method removes the lock identified by the lock token
          in the State-Token header from the Request-URI, and all other
          resources included in the lock.
          
          
          5.5.2     Example
          
          UNLOCK /workspace/webdav/info.doc HTTP/1.1
          Host: webdav.sb.aol.com
          State-Token: OpaqueLockToken:123AbcEfg1284h23h2
          
          HTTP/1.1 200 OK
          
          In this example, the lock identified by the lock token
          "OpaqueLockToken:123AbcEfg1284h23h2" is successfully removed from
          the resource http://webdav.sb.aol.com/workspace/webdav/info.doc.
          If this lock included more than just one resource, the lock is
          removed from those resources as well.
          
          
          5.6  Discovery Mechanisms
          
          
          5.6.1     Lock Capability Discovery
          
          
          5.6.1.1   Problem Definition
          
          Since server lock support is optional, a client trying to lock a
          resource on a server can either try the lock and hope for the
          best, or perform some form of discovery to determine what lock
          capabilities the server supports.  This is known as lock
          capability discovery. Lock capability discovery differs from
          discovery of supported access control types, since there may be
          access control types without corresponding lock types.
          
          
          5.6.1.2   SupportedLock Property
          
          Name: http://www.ietf.org/standards/dav/lock/supportedlock
          Purpose: To provide a listing of the lock capabilities supported
          by the resource.
          Schema: http://www.ietf.org/standards/dav/
          Values: An XML document containing zero or more LockEntry XML
          elements.
          Description: The SupportedLock property of a resource returns a
          listing of the combinations of scope and access types which may
          be specified in a lock request on the resource. Note that the
          actual contents are themselves controlled by access controls so a
          
          
          
          
          
          
          server is not required to provide information the client is not
          authorized to see. If SupportedLock is available on "*" then it
          MUST define the set of locks allowed on all resources on that
          server.
          
          
          5.6.1.3   LOCKENTRY XML Element
          
          Name: http://www.ietf.org/standards/dav/lockentry
          Purpose: Defines a DAVLockType/LockScope pair which may be
          legally used with a LOCK on the specified resource.
          Schema: http://www.ietf.org/standards/dav/
          Parent: A SupportedLock entry
          Values: LockType LockScope
          
          
          5.6.1.4   LOCKTYPE XML Element
          
          Name: http://www.ietf.org/standards/dav/locktype
          Purpose: Lists a DAVLockType
          Schema: http://www.ietf.org/standards/dav/
          Parent: LOCKENTRY
          Values: DAVLockTypeValue
          
          
          5.6.1.5   LOCKSCOPE XML Element
          
          Name: http://www.ietf.org/standards/dav/lockscope
          Purpose: Lists a DAVLockScope
          Schema: http://www.ietf.org/standards/dav/
          Parent: LOCKENTRY
          Values: DAVLockScopeValue
          
          
          5.6.1.6   Example
          
          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "D"/>
          <D:PROPFIND>
               <prop><SupportedLock/></prop>
          </D:PROPFIND>
          
          HTTP/1.1 207 Multi-Response
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
               href ="http://www.ietf.org/standards/dav/" AS = "D"/>
          <D:MultiResponse>
               <Response>
                    <Prop>
                         <SupportedLock>
                              <LockEntry>
                                   <LockType>Write</LockType>
                                   <LockScope>Exclusive</LockScope>
                              </LockEntry>
                              <LockEntry>
                                   <LockType>Write</LockType>
                                   <LockScope>Shared</LockScope>
                              </LockEntry>
          
          
          
          
          
          
                         </SupportedLock>
                    </Prop>
                    <Status>HTTP/1.1 200 Success</Status>
          </Response>
          </D:MultiResponse>
          
          
          5.6.2     Active Lock Discovery
          
          
          5.6.2.1   Problem Definition
          
          If another principal locks a resource that a principal wishes to
          access, it is useful for the second principal to be able to find
          out who the first principal is.
          
          
          5.6.2.2   Solution Requirements
          
          The lock discovery mechanism should provide a list of who has the
          resource locked, what locks they have, and what their lock tokens
          are. The lock tokens are useful in shared lock situations where
          two principals may want to guarantee that they do not overwrite
          each other. The lock tokens are also useful for administrative
          purposes so that an administrator can remove a lock by referring
          to its token.
          
          
          5.6.2.3   LOCKDISCOVERY Property
          
          Name: http://www.ietf.org/standards/dav/lockdiscovery
          Purpose: To discover what locks are active on a resource
          Schema: http://www.ietf.org/standards/dav/
          Values= An XML document containing zero or more ActiveLock XML
          elements.
          
          Description: The LOCKDISCOVERY property returns a listing of who
          has a lock, what type of lock they have, the time out type and
          the time remaining on the time out, and the associated lock
          token. The server is free to withhold any or all of this
          information if the requesting principal does not have sufficient
          access rights to see the requested data. A server which supports
          locks MUST provide the LOCKDISCOVERY property on any resource
          with locks on it.
          
          
          5.6.2.4   ACTIVELOCK XML Element
          
          Name: http://www.ietf.org/standards/dav/activelock
          Purpose: A multivalued XML element that describes a particular
          active lock on a resource
          Schema: http://www.ietf.org/standards/dav/
          Parent: A LOCKDISCOVERY entry
          Values= LOCKTYPE LOCKSCOPE [ADDLOCKS] OWNER TIMEOUT LOCKTOKEN
          
          
          5.6.2.5   OWNER XML Element
          
          Name: http://www.ietf.org/standards/dav/lock/owner
          Purpose: Returns owner information
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= XML:REF | {any valid XML string}
          
          
          
          
          
          
          5.6.2.6   TIMEOUT XML Element
          
          Name: http://www.ietf.org/standards/dav/timeout
          Purpose: Returns information about the timeout associated with
          the lock
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= TimeType
          
          
          5.6.2.7   ADDLOCKS XML Element
          
          Name:     http://www.ietf.org/standards/dav/addlocks
          Purpose: Lists additional resources associated with this lock, if
          any.
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= 1*HREF
          
          
          5.6.2.8   LOCKTOKEN XML Element
          
          Name: http://www.ietf.org/standards/dav/statetoken
          Purpose: Returns the lock token
          Schema: http://www.ietf.org/standards/dav/
          Parent: ACTIVELOCK
          Values= HREF
          Description: The HREF contains a Lock-Token-URL.
          
          
          5.6.2.9   Example
          
          PROPFIND  /container/ HTTP/1.1
          Host: www.foo.bar
          Content-Length: xxxx
          Content-Type: text/xml
          
          <?XML:Namespace href =
               "http://www.ietf.org/standards/dav/" AS = "D"/>
          <D:PROPFIND>
               <prop><lockdiscovery/></prop>
          </D:PROPFIND>
          
          HTTP/1.1 207 Multi-Response
          Content-Type: text/xml
          Content-Length: xxxxx
          
          <?XML:Namespace
               href ="http://www.ietf.org/standards/dav/" AS = "D"/>
          <D:MultiResponse>
               <Response>
                    <Prop>
                         <lockdiscovery>
                              <activelock>
                                   <locktype>write</locktype>
                                   <lockscope>exclusive</lockscope>
                                   <addlocks>
                                        <HREF>http://foo.com/doc/</HREF>
                                   </addlocks>
                                   <owner>Jane Smith</owner>
                                   <timeout>Infinite</timeout>
                                   <locktoken>
                                        <HREF>iamuri:unique!!!!!</HREF>
                                   </locktoken>
                              </activelock>
          
          
          
          
          
          
                         </lockdiscovery>
                    </Prop>
                    <Status>HTTP/1.1 200 Success</Status>
          </Response>
          </D:MultiResponse>
          
          This resource has a single exclusive write lock on it, with an
          infinite time out. This same lock also covers the resource
          http://foo.com/doc/.
          
          
          6    Version Control
          [TBD]
          
          
          7    Internationalization Support
          [TBD]
          
          
          8    Security Considerations
          [TBD]
          
          
          9    Copyright
          
          Copyright (C) The Internet Society October 13, 1997. All Rights
          Reserved.
          
          This document and translations of it may be copied and furnished
          to others, and derivative works that comment on or otherwise
          explain it or assist in its implementation may be prepared,
          copied, published and distributed, in whole or in part, without
          restriction of any kind, provided that the above copyright notice
          and this paragraph are included on all such copies and derivative
          works.  However, this document itself may not be modified in any
          way, such as by removing the copyright notice or references to
          the Internet Society or other Internet organizations, except as
          needed for the purpose of developing Internet standards in which
          case the procedures for copyrights defined in the Internet
          Standards process must be followed, or as required to translate
          it into languages other than English.
          
          The limited permissions granted above are perpetual and will not
          be revoked by the Internet Society or its successors or
          assignees.
          
          This document and the information contained herein is provided on
          an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
          ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
          IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
          OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
          IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
          PURPOSE.
          
          
          10   Acknowledgements
          
          Terry Allen, Harald Alvestrand, Alan Babich, Dylan Barrell,
          Bernard Chester, Dan Connolly, Jim Cunningham, Ron Daniel, Jr.,
          Jim Davis, Keith Dawson, Mark Day, Martin Duerst, David Durand,
          Lee Farrell, Chuck Fay, Roy Fielding, Mark Fisher, Alan Freier,
          George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
          Hamilton, Steve Henning, Alex Hopmann, Andre van der Hoek, Ben
          Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven Martin,
          Larry Masinter, Michael Mealling, Keith Moore, Henrik Nielsen,
          
          
          
          
          
          
          Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff, Saveen Reddy,
          Henry Sanders, Christopher Seiwald, Judith Slein, Mike Spreitzer,
          Einar Stefferud, Ralph Swick, Kenji Takahashi, Robert Thau, John
          Turner, Sankar Virdhagriswaran, Fabio Vitali, Gregory Woodhouse,
          Lauren Wood
          
          
          11   References
          
          [Berners-Lee, 1997] T. Berners-Lee, "Metadata Architecture."
          Unpublished white paper, January 1997.
          http://www.w3.org/pub/WWW/DesignIssues/Metadata.html.
          
          [Bradner, 1997] S. Bradner, "Key words for use in RFCs to
          Indicate  Requirement Levels."  RFC 2119, BCP 14. Harvard
          University.  March, 1997.
          
          
          [Bray, Sperberg-McQueen, 1997] T. Bray, C. M. Sperberg-McQueen,
          "Extensible Markup Language (XML): Part I. Syntax", WD-xml-
          lang.html, http://www.w3.org/pub/WWW/TR/WD-xml-lang.html.
          
          [Connolly et al, 1997] D. Connolly, R. Khare, H.F. Nielsen, "PEP
          - an Extension Mechanism for HTTP", Internet draft, work-in-
          progress. draft-ietf-http-pep-04.txt,
          ftp://ds.internic.net/internet-drafts/draft-ietf-http-pep-04.txt.
          
          [Fielding et al., 1997] R. Fielding, J. Gettys, J. Mogul, H.
          Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol --
          HTTP/1.1." RFC 2068. U.C. Irvine, DEC, MIT/LCS.  January, 1997.
          ftp://ds.internic.net/rfc/rfc2068.txt
          
          [Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for
          Bibliographic Records," RFC 1807. Stanford, Myricom. June, 1995.
          ftp://ds.internic.net/rfc/rfc1807.txt
          
          [Maloney, 1996] M. Maloney, "Hypertext Links in HTML." Internet
          draft (expired), work-in-progress, January, 1996.
          
          [MARC, 1994] Network Development and MARC Standards, Office, ed.
          1994. "USMARC Format for Bibliographic Data", 1994. Washington,
          DC: Cataloging Distribution Service, Library of Congress.
          
          [Miller et al., 1996] J. Miller, T. Krauskopf, P. Resnick, W.
          Treese, "PICS Label Distribution Label Syntax and Communication
          Protocols" Version 1.1, W3C Recommendation REC-PICS-labels-
          961031. http://www.w3.org/pub/WWW/TR/REC-PICS-labels-961031.html.
          
          [Slein et al., 1997] J. A. Slein, F. Vitali, E. J. Whitehead,
          Jr., D. Durand, "Requirements for Distributed Authoring and
          Versioning on the World Wide Web." Internet-draft, work-in-
          progress, draft-ietf-webdav-requirements-04.txt,
          ftp://ds.internic.net/internet-drafts/draft-ietf-webdav-
          requirements-04.txt.
          
          [WebDAV, 1997] WEBDAV Design Team. "A Proposal for Web Metadata
          Operations." Unpublished manuscript.
          http://www.ics.uci.edu/~ejw/authoring/proposals/metadata.html
          
          [Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R. Daniel,
          "OCLC/NCSA Metadata Workshop Report."
          http://purl.oclc.org/metadata/dublin_core_report.
          
          [Yergeau, 1997] F. Yergeau, "UTF-8, a transformation format of
          Unicode and ISO 10646", Internet Draft, work-in-progress, draft-
          
          
          
          
          
          
          yergeau-utf8-rev-00.txt, http://www.internic.net/internet-
          drafts/draft-yergeau-utf8-rev-00.txt.
          
          
          12   Authors' Addresses
          
          Y. Y. Goland
          Microsoft Corporation
          One Microsoft Way
          Redmond, WA 98052-6399
          Email yarong@microsoft.com
          
          E. J. Whitehead, Jr.
          Dept. Of Information and Computer Science
          University of California, Irvine
          Irvine, CA 92697-3425
          Email: ejw@ics.uci.edu
          
          A. Faizi
          Netscape
          685 East Middlefield Road
          Mountain View, CA 94043
          Email: asad@netscape.com
          
          S. R Carter
          Novell
          1555 N. Technology Way
          M/S ORM F111
          Orem, UT 84097-2399
          Email srcarter@novell.com
          
          D. Jensen
          Novell
          1555 N. Technology Way
          M/S ORM F111
          Orem, UT 84097-2399
          Email dcjensen@novell.com
          

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