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Versions: (draft-rosenberg-simple-xcap-package) 00 01 02 03 draft-ietf-simple-xcap-diff

SIMPLE                                                      J. Rosenberg
Internet-Draft                                               dynamicsoft
Expires: January 16, 2005                                  July 18, 2004


   An Extensible Markup Language (XML) Document Format for Indicating
     Changes in XML Configuration Access  Protocol (XCAP) Resources
                   draft-ietf-simple-xcap-package-02

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 16, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This specification defines a document format that can be used to
   describe the differences between versions of resources managed by the
   Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP).  Documents of this format can be delivered to clients using a
   number of means, including the Session Initiation Protocol (SIP)
   event package for configuration data.  By subscribing to this event
   package, clients can learn about document changes made by other
   clients.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Structure of an XCAP Diff Document . . . . . . . . . . . . . .  4
   3.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Example Document . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Usage with the Config Framework  . . . . . . . . . . . . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
     7.1   application/xcap-diff+xml MIME Type  . . . . . . . . . . . 13
     7.2   URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:xcap-diff . . . . . . . . . . . . . 13
     7.3   Schema Registration  . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   8.1   Normative References . . . . . . . . . . . . . . . . . . . . 15
   8.2   Informative References . . . . . . . . . . . . . . . . . . . 15
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 16
       Intellectual Property and Copyright Statements . . . . . . . . 17

































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1.  Introduction

   The Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP) [7] is a protocol that allows clients to manipulate XML
   documents stored on a server.  These XML documents serve as
   configuration information for application protocols.  As an example,
   resource list [11] subscriptions (also known as presence lists) allow
   a client to have a single SIP subscription to a list of users, where
   the list is maintained on a server.  The server will obtain presence
   for those users and report it back to the client.  This application
   requires the server, called a Resource List Server (RLS), to have
   access to the list of presentities.  This list needs to be
   manipulated by clients so they can add and remove their friends as
   they desire.

   Complexities arise when multiple clients attempt to simultaneously
   manipulate a document, such as a presence list.  Frequently, a client
   will keep a copy of the current list in memory, so it can render it
   to users.  However, if another client modifies the document, the
   cached version becomes stale.  This information must be made known to
   all clients which have cached copies of the document, so that they
   can fetch the most recent one.

   To deal with this problem, clients can use the Session Initiation
   Protocol (SIP) [9]event package [10] for subscribing to changes in
   configuration and profile information [8], including application data
   that resides on an XCAP server.  With that package, a user gets
   notified that a particular document has changed.  This notification
   can include the full content of the new document, or it can be a
   content indirection [14].  However, in both cases, the transfer of
   the entire document is ultimately required.  This may require a lot
   of bandwidth, particularly for wireless devices with large documents
   (such as a resource list [11] with hundreds of users listed).

   To resolve this problem, this document defines a data format which
   can convey changes in XML documents managed by an XCAP server.  This
   data format is an XML document format, called an XCAP diff document.
   This specification also explains how this format is used in
   conjunction with the configuration profile framework.












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2.  Structure of an XCAP Diff Document

   An XCAP diff document is an XML [2] document that MUST be well-formed
   and SHOULD be valid.  XML-change documents MUST be based on XML 1.0
   and MUST be encoded using UTF-8.  This specification makes use of XML
   namespaces for identifying xml-change documents and document
   fragments.  The namespace URI for elements defined by this
   specification is a URN [3], using the namespace identifier 'ietf'
   defined by [5] and extended by [6].  This URN is:
      urn:ietf:params:xml:ns:xcap-diff

   An XCAP diff document begins with the root element tag <xcap-diff>.
   This element has a single mandatory attribute, "xcap-root".  The
   value of this attribute is the XCAP root URI in which the changes
   have taken place.  A single XCAP diff document can only represent
   changes in documents within the same XCAP root.  The content of the
   <xcap-diff> element is a sequence of <document> elements.  Each
   <document> element specifies changes in a specific document within
   the XCAP root.  It has three mandatory attributes - "new-etag",
   "previous-etag" and "doc-selector", and a single optional attribute,
   "hash".  The "doc-selector" identifies the specific document within
   the XCAP root for which changes are included.  Its content MUST be a
   relative path reference, with the base URL being equal to the XCAP
   root URL.  The "previous-etag" and "new-etag" provide indentifiers
   for the document instance before the change, and then after the
   change.  These need not have been sequentially assigned etags at the
   server.  An XCAP diff document can describe changes that have
   occurred over a series of XCAP operations.

   The optional "hash" attribute provides an HMAC of the new document,
   represented in canonical form.  See Section 5 for details on how this
   value is computed.  This attribute is optional, and a server can
   elect not to include it.

   Each <document> element is followed by a series of operations, which
   if followed by the client, will convert the document whose etag is
   "previous-etag" into the one whose etag is "new-etag".  Each
   operation is specified by an XML element.  Six operations are
   defined:
   <add-element>: Instructs the recipient of the document to add an
      element.  The "parent" attribute contains a node-selector which
      selects the parent of the new element.  The "position" attribute
      indicates that the new element is to be inserted as a child such
      that it has that position amongst it siblings.  The content of
      <add-element> MUST be a CDATA section enclosing a single XML
      element, which is to be added.





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   <add-attribute>: Instructs the recipient of the document to add an
      attribute.  The "element" attribute contains a node-selector which
      selects the element into which the attribute is to be inserted.
      The "att-name" attribute contains the name of the new attribute.
      The content of <add-attribute> is the value of the new attribute.
   <remove-element>: Instructs the recipient of the document to delete
      an element.  The "element" attribute contains a node-selector
      which selects the element to be removed.
   <remove-attribute>: Instructs the recipient of the document to remove
      an attribute.  The "element" attribute contains a node-selector
      which selects the element in which the attribute exists.  The
      "att-name" attribute indicates the name of the attribute which is
      to be removed.
   <replace-element>: Instructs the recipient of the document to replace
      an element.  The "element" attribute contains a node-selector
      which selects the element to replace.  The content of the
      <replace-element> element MUST be a CDATA section containing
      single XML element which is to replace the one identified by the
      node-selector.
   <replace-attribute>: Instructs the recipient of the document to
      replace an attribute.  The "element" attribute contains a
      node-selector which selects the element to replace.  The
      "att-name" attribute contains the name of the attribute to
      replace.  The content of the <replace-attribute> element is the
      value of the new attribute.

   When the node selector appears as an attribute value, any quotation
   marks MUST be replaced with &quot;.

   It is possible for the list of instructions for a <document> to be
   empty.  In that case, the entity tag in the "new-etag" may equal the
   entity tag in the "previous-etag".  These entity tags may differ in
   the event that the document has changed entity tags, but its content
   has not been altered.

















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3.  XML Schema


   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:xcap-diff"
    xmlns:tns="urn:ietf:params:xml:ns:xcap-diff"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    elementFormDefault="qualified" attributeFormDefault="unqualified">
    <xs:element name="xcap-diff">
     <xs:complexType>
      <xs:sequence>
       <xs:element name="document" maxOccurs="unbounded">
        <xs:complexType>
         <xs:sequence minOccurs="0" maxOccurs="unbounded">
          <xs:choice>
           <xs:element name="add-element">
            <xs:complexType>
             <xs:simpleContent>
              <xs:extension base="xs:string">
               <xs:attribute name="parent" type="xs:string" use="required"/>
               <xs:attribute name="position" type="xs:int" use="required"/>
              </xs:extension>
             </xs:simpleContent>
            </xs:complexType>
           </xs:element>
           <xs:element name="add-attribute">
            <xs:complexType>
             <xs:simpleContent>
              <xs:extension base="xs:string">
               <xs:attribute name="element" type="xs:string" use="required"/>
               <xs:attribute name="att-name" type="xs:string" use="required"/>
              </xs:extension>
             </xs:simpleContent>
            </xs:complexType>
           </xs:element>
           <xs:element name="remove-element">
            <xs:complexType>
             <xs:attribute name="element" type="xs:string" use="required"/>
            </xs:complexType>
           </xs:element>
           <xs:element name="remove-attribute">
            <xs:complexType>
             <xs:attribute name="element" type="xs:string" use="required"/>
             <xs:attribute name="att-name" type="xs:string" use="required"/>
            </xs:complexType>
           </xs:element>
           <xs:element name="replace-element">
            <xs:complexType>



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             <xs:simpleContent>
              <xs:extension base="xs:string">
               <xs:attribute name="element" type="xs:string" use="required"/>
              </xs:extension>
             </xs:simpleContent>
            </xs:complexType>
           </xs:element>
           <xs:element name="replace-attribute">
            <xs:complexType>
             <xs:simpleContent>
              <xs:extension base="xs:string">
               <xs:attribute name="element" type="xs:string" use="required"/>
               <xs:attribute name="att-name" type="xs:string" use="required"/>
              </xs:extension>
             </xs:simpleContent>
            </xs:complexType>
           </xs:element>
          </xs:choice>
         </xs:sequence>
         <xs:attribute name="doc-selector" type="xs:anyURI" use="required"/>
         <xs:attribute name="new-etag" type="xs:string" use="required"/>
         <xs:attribute name="previous-etag" type="xs:string" use="required"/>
         <xs:attribute name="hash" type="xs:string" use="optional"/>
        </xs:complexType>
       </xs:element>
      </xs:sequence>
      <xs:attribute name="xcap-root" type="xs:anyURI" use="required"/>
     </xs:complexType>
    </xs:element>
   </xs:schema>





















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4.  Example Document

   The following is an example of a document compliant to the schema:


   <?xml version="1.0" encoding="UTF-8"?>
   <xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <document doc-selector="resource-lists/users/joe/friends"
     new-etag="7hahsd" previous-etag="7hahsd"/>
    <document doc-selector="resource-lists/users/joe/coworkers"
     new-etag="ffds66a" previous-etag="xkkkaisu">
      <add-element parent="resource-lists/list[@name=&quot;l1&quot;]"
       position="1"><![CDATA[<entry uri="sip:new-worker@example.com"/>]
   ]></add-element>
    </document>
   </xcap-diff>


































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5.  Usage with the Config Framework

   The framework for user agent profile delivery [8] defines an event
   package which can be used to subscribe to user, device, application
   or local-network data.  This data can be present in an XCAP server.
   Normally, content indirection [14] will be used as the NOTIFY body
   format, to indicate the specific document that has changed, and
   should be re-fetched.  However, if the client includes an Accept
   header field including the MIME type "application/xcap-diff+xml", the
   server has the option of returning documents in this format instead.

   When the client performs an initial subscription, the rules in [8]
   are used to select the set of documents which the subscription
   applies to.  Upon initial subscription, the server does not know
   which instance (where each instance is identified by an etag) the
   client currently posessses, if any.  Indeed, upon startup, the client
   will not have any documents.  The initial NOTIFY in this case MUST
   include a <document> element for each document associated with the
   subscription.  The content of each of those <document> elements MUST
   be empty.  The "previous-etag" and "new-etag" attributes MUST be
   identical, and contain the entity tag for the current version of that
   resource.  An XML diff document structured this way is called a
   "reference" XML diff document.  It establishes the baseline etags and
   document URIs for the documents covered by the subscription.

   Upon receipt of this document, the client can determine whether its
   local instance documents, if any, match the etags in the XCAP diff
   document.  If they do not match, the client SHOULD perform a
   conditional GET for each document.  The document URI is constructed
   by appending the XCAP root in the "xcap-root" attribute of the
   <xcap-diff> element to the escape coded "doc-selector" from each
   <document> element.  The request is made conditional by including an
   If-Match header field, with the value of the etag from each
   <document> element.  So long as the documents haven't changed between
   the NOTIFY and the GET, the client will obtain the reference versions
   that the server will use for subsequent notifications.

   If the conditional GET should fail, the client SHOULD generate a
   SUBSCRIBE refresh request to trigger a new NOTIFY.  The server will
   always generate a "reference" XML diff document on receipt of a
   SUBSCRIBE refresh.  This establish a new set of baseline etags, and
   the client can then attempt to do another fetch.  It is anticipated
   that future extensions to the profile delivery framework will allow a
   client to include, in its SUBSCRIBE request, an indicator of the
   current version of the documents it holds.  That would obviate the
   need for a potentially never-ending stream of SUBSCRIBE/GET sequences
   should the documents be rapidly changing, for some reason.




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   Once the client has obtained the versions of the documents identified
   in the reference XML diff, it can process NOTIFY requests on that
   subscription.  To process the NOTIFY requests, it makes sure that its
   current version matches the version in the "previous-etag" attribute
   of the <document> element.  It then follows the list of instructions,
   in order, for that <document>.  Specifically:
   <add-element>: The "parent" attribute contains a node-selector.  The
      client applies the node selector to the document according to the
      procedures defined in XCAP [7].  If the result is a single
      element, the client takes the content of the <add-element> element
      and adds it as the position-th child.  If the node selector doesnt
      select a single element, or the selected element has fewer than
      position-1 children already, the result is an error.  The client
      MUST discard the XCAP-diff document, and MUST flush its current
      version of the document from memory.  It can then obtain a new XML
      diff reference by sending a SUBSCRIBE refresh request on the
      dialog.
   <add-attribute>: The "element" attribute contains a node-selector.
      The client applies the node selector to the document according to
      the procedures defined in XCAP [7].  If the result is a single
      element, the client takes adds a new attribute to the element,
      with the name equal to the content of the "att-name" attribute,
      and a value equal to the content of the <add-attribute> element.
      If the node selector doesnt select a single element, or the
      selected element already has an attribute with that name, the
      result is an error.  The client MUST discard the XCAP-diff
      document, and MUST flush its current version of the document from
      memory.  It can then obtain a new XML diff reference by sending a
      SUBSCRIBE refresh request on the dialog.
   <remove-element>: The "element" attribute contains a node-selector.
      The client applies the node selector to the document according to
      the procedures defined in XCAP [7].  If the result is a single
      element, the client removes that element from the document.  If
      the node selector doesnt select a single element the result is an
      error.  The client MUST discard the XCAP-diff document, and MUST
      flush its current version of the document from memory.  It can
      then obtain a new XML diff reference by sending a SUBSCRIBE
      refresh request on the dialog.
   <remove-attribute>: The "element" attribute contains a node-selector.
      The client applies the node selector to the document according to
      the procedures defined in XCAP [7].  If the result is a single
      element, the client removes the attribute whose name is
      "att-name".  If the node selector doesnt select a single element,
      or the selected element doesn't have an attribute with that name,
      the result is an error.  The client MUST discard the XCAP-diff
      document, and MUST flush its current version of the document from
      memory.  It can then obtain a new XML diff reference by sending a
      SUBSCRIBE refresh request on the dialog.



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   <replace-element>: The "element" attribute contains a node-selector.
      The client applies the node selector to the document according to
      the procedures defined in XCAP [7].  If the result is a single
      element, the client removes that element, and replaces it with the
      content of the <add-element> element.  If the node selector doesnt
      select a single element, the result is an error.  The client MUST
      discard the XCAP-diff document, and MUST flush its current version
      of the document from memory.  It can then obtain a new XML diff
      reference by sending a SUBSCRIBE refresh request on the dialog.
   <replace-attribute>: The "element" attribute contains a
      node-selector.  The client applies the node selector to the
      document according to the procedures defined in XCAP [7].  If the
      result is a single element, the client removes the content of the
      attribute whose name is "att-name", and replaces it with the
      content of the <replace-attribute> element.  If the node selector
      doesnt select a single element, or the selected element doesn't
      have an attribute with that name, the result is an error.  The
      client MUST discard the XCAP-diff document, and MUST flush its
      current version of the document from memory.  It can then obtain a
      new XML diff reference by sending a SUBSCRIBE refresh request on
      the dialog.

   Once the client has finished applying the instructions to the
   document, it should end up with the same document the server has.  To
   verify this, the client applies the mandatory XML canonicalization
   defined in the Canonical XML 1.0 [1] specification, and computes an
   HMAC [12] using SHA1 over this canonical document, with a key whose
   value is 0x2238a.  The resulting string is compared with the "hash"
   attribute of the <document> element.  If they match, the client can
   be sure that it has the most up to date version.  If they don't
   match, the client MUST flush its current version of the document from
   memory.  It can then obtain a new XML diff reference by sending a
   SUBSCRIBE refresh request on the dialog.

   Of course, this mechanism for computing the most current document
   from the hash is optional.  A client can elect to ignore the
   information on what changed and simply fetch the most recent document
   every time it gets a change indication where the new version is not
   the same as the one cached by the client.  Furthermore, the server
   may elect to not send the hash, in which case this check cannot be
   made.










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6.  Security Considerations

   XCAP diff documents contain the same information in the documents
   whose differences they describe.  As such, the security
   considerations associated with those documents apply to XCAP diff
   documents.













































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7.  IANA Considerations

   There are several IANA considerations associated with this
   specification.

7.1  application/xcap-diff+xml MIME Type
      MIME media type name: application
      MIME subtype name: xcap-diff+xml
      Mandatory parameters: none
      Optional parameters: Same as charset parameter application/xml as
      specified in RFC 3023 [4].
      Encoding considerations: Same as encoding considerations of
      application/xml as specified in RFC 3023 [4].
      Security considerations: See Section 10 of RFC 3023 [4] and
      Section 6 of RFCXXXX [[NOTE TO RFC-EDITOR/IANA: Please replace
      XXXX with the RFC number of this specification.]].
      Interoperability considerations: none.
      Published specification: This document.
      Applications which use this media type: This document type has
      been used to support manipulation of resource lists [13] using
      XCAP.
      Additional Information:
         Magic Number: None
         File Extension: .xdf or .xml
         Macintosh file type code: "TEXT"
         Personal and email address for further information: Jonathan
         Rosenberg, jdrosen@jdrosen.net
         Intended usage: COMMON
         Author/Change controller: The IETF.

7.2  URN Sub-Namespace Registration for urn:ietf:params:xml:ns:xcap-diff

   This section registers a new XML namespace, as per the guidelines in
   [6]
      URI: The URI for this namespace is
      urn:ietf:params:xml:ns:xcap-diff.
      Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
      Jonathan Rosenberg (jdrosen@jdrosen.net).
      XML:












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                BEGIN
                <?xml version="1.0"?>
                <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
                          "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
                <html xmlns="http://www.w3.org/1999/xhtml">
                <head>
                  <meta http-equiv="content-type"
                     content="text/html;charset=iso-8859-1"/>
                  <title>XCAP Diff Namespace</title>
                </head>
                <body>
                  <h1>Namespace for XCAP Diff</h1>
                  <h2>urn:ietf:params:xml:ns:xcap-diff</h2>
                  <p>See <a href="[URL of published RFC]">RFCXXXX[[NOTE
   TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this
   specification.]]</a>.</p>
                </body>
                </html>
                END


7.3  Schema Registration

   This section registers a new XML schema per the procedures in [6].
      URI: urn:ietf:params:xml:schema:xcap-diff
      Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
      Jonathan Rosenberg (jdrosen@jdrosen.net).
      The XML for this schema can be found as the sole content of
      Section 3.






















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8.  References

8.1  Normative References

   [1]  Boyer, J., "Canonical XML Version 1.0", W3C REC
        REC-xml-c14n-20010315, March 2001.

   [2]  Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
        "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
        FirstEdition REC-xml-20001006, October 2000.

   [3]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [4]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
        3023, January 2001.

   [5]  Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
        August 1999.

   [6]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
        2004.

   [7]  Rosenberg, J., "The Extensible Markup Language (XML)
        Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-02
        (work in progress), February 2004.

   [8]  Petrie, D., "A Framework for Session Initiation Protocol User
        Agent Profile Delivery", draft-ietf-sipping-config-framework-03
        (work in progress), May 2004.

8.2  Informative References

   [9]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
         Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
         Session Initiation Protocol", RFC 3261, June 2002.

   [10]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
         Notification", RFC 3265, June 2002.

   [11]  Roach, A., Rosenberg, J. and B. Campbell, "A Session Initiation
         Protocol (SIP) Event Notification Extension for  Resource
         Lists", draft-ietf-simple-event-list-04 (work in progress),
         June 2003.

   [12]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
         for Message Authentication", RFC 2104, February 1997.

   [13]  Rosenberg, J., "An Extensible Markup Language (XML)



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         Configuration Access Protocol (XCAP)  Usage for Presence
         Lists", draft-ietf-simple-xcap-list-usage-02 (work in
         progress), February 2004.

   [14]  Olson, S., "A Mechanism for Content Indirection in Session
         Initiation Protocol (SIP)  Messages",
         draft-ietf-sip-content-indirect-mech-03 (work in progress),
         June 2003.


Author's Address

   Jonathan Rosenberg
   dynamicsoft
   600 Lanidex Plaza
   Parsippany, NJ  07054
   US

   Phone: +1 973 952-5000
   EMail: jdrosen@dynamicsoft.com
   URI:   http://www.jdrosen.net






























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