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Versions: (draft-reddy-dasl-protocol) 00

INTERNET-DRAFT                                       Saveen Reddy,
                                                     Microsoft
draft-ietf-dasl-protocol-00.txt                      Dale Lowry, Novell
                                                     Surendra Reddy,
                                                     Oracle
                                                     Rick Henderson,
                                                     Netscape
                                                     Jim Davis, CourseNet
                                                     Alan Babich, Filenet

Expires December 24, 1999                             June 24, 1999

                       DAV Searching & Locating

   Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet drafts are
   working documents of the Internet Engineering Task Force (IETF),
   its areas and its working groups. Note that other groups may also
   distribute working information as Internet drafts.

   Internet Drafts are draft documents valid for a maximum of six months
   and can be updated, replaced or obsoleted by other documents at any
   time. It is inappropriate to use Internet drafts as reference material
   or to cite them as 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.

   Distribution of this document is unlimited. Please send comments to
   the mailing list at <www-webdav-dasl@w3.org>, which may be joined by
   sending a message with subject "subscribe" to
   <www-webdav-dasl-request@w3.org>.

   Discussions of the list are archived at <URL:
   http://www.w3.org/pub/WWW/Archives/Public/www-webdav-dasl >.

   Abstract

   This document specifies a set of methods, headers, and content-types
   composing DASL, an application of the HTTP/1.1 protocol to efficiently
   search for DAV resources based upon a set of client-supplied criteria.

1. Introduction

1.1 DASL

   This document defines DAV Searching & Locating (DASL), an application
   of HTTP/1.1 forming a lightweight search protocol to transport queries
   and result sets and allows clients to make use of server-side search
   facilities. [DASLREQ] describes the motivation for DASL.

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   DASL will minimize the complexity of clients so as to facilitate
   widespread deployment of applications capable of utilizing the DASL
   search mechanisms.

   DASL consists of:
     * the SEARCH method,
     * the DASL response header,
     * the DAV:searchrequest XML element,
     * the DAV:queryschema property,
     * the DAV:basicsearch XML element and query grammar, and
     * the DAV:basicsearchschema XML element.

1.2 Relationship to DAV

   DASL relies on the resource and property model defined by [WebDAV].
   DASL does not alter this model. Instead, DASL allows clients to access
   DAV-modeled resources through server-side search.

1.3 Terms

   This draft uses the terms defined in [RFC2068], [WebDAV], and
   [DASLREQ].

1.4 Notational Conventions

   The augmented BNF used by this document to describe protocol elements
   is exactly the same as the one described in Section 2.1 of [RFC2068].
   Because this augmented BNF uses the basic production rules provided in
   Section 2.2 of [RFC2068], those rules apply to this document as well.

   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 [RFC2119].

1.5 An Overview of DASL at Work

   One can express the basic usage of DASL in the following steps:
     * The client constructs a query using the DAV:basicsearch grammar.
     * The client invokes the SEARCH method on a resource that will
       perform the search (the search arbiter) and includes a text/xml
       request entity that contains the query.
     * The search arbiter performs the query.
     * The search arbiter sends the results of the query back to the
       client in the response. The server MUST send a text/xml entity
       that matches the [WebDAV] PROPFIND response.

2. The SEARCH Method






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 2.1 Overview

   The client invokes the SEARCH method to initiate a server-side search.
   The body of the request defines the query. The server MUST emit
   text/xml entity matching the [WebDAV] PROPFIND response.

   The SEARCH method plays the role of transport mechanism for the query
   and the result set. It does not define the semantics of the query. The
   type of the query defines the semantics.

2.2 The Request

   The client invokes the SEARCH method on the resource named by the
   Request-URI.

2.2.1 The Request-URI

   The Request-URI identifies the search arbiter.

   The SEARCH method defines no relationship between the arbiter and the
   scope of the search, rather the particular query grammar used in the
   query defines the relationship. For example, the FOO query grammar may
   force the request-URI to correspond exactly to the search scope.

2.2.2 The Request Body

   The server MUST process a text/xml or application/xml request body,
   and MAY process request bodies in other formats. See [RFC 2376] for
   guidance on packaging XML in requests.

   If the client sends a text/xml or application/xml body, it MUST
   include the DAV:searchrequest XML element. The DAV:searchrequest XML
   element identifies the query grammar, defines the criteria, the result
   record, and any other details needed to perform the search.

2.3 The DAV:searchrequest XML Element

   <!ELEMENT searchrequest ANY > The DAV:searchrequest XML element
   contains a single XML element that defines the query. The name of the
   query element defines the type of the query. The value of that element
   defines the query itself.

2.4 The Successful 207 (Multistatus) Response

   If the server returns 207 (Multistatus), then the search proceeded
   successfully and the response MUST match that of a PROPFIND.

   There MUST be one DAV:response for each resource that matched the
   search criteria. For each such response, the DAV:href element contains
   the URI of the resource, and the response MUST include a DAV:propstat
   element.


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  In addition, the server MAY include DAV:response items in the reply where
   the DAV:href element contains a URI that is not a matching resource,
   e.g. that of a scope or the query arbiter. Each such response item
   MUST NOT contain a DAV:propstat element, and MUST contain a DAV:status
   . It SHOULD contain a DAV:responsedescription .

2.4.1 Extending the PROPFIND Response

   A response MAY include more information than PROPFIND defines so long
   as the extra information does not invalidate the PROPFIND response.
   Query grammars SHOULD define how the response matches the PROPFIND
   response.

2.4.1 Example: A Simple Request and Response

   This example demonstrates the request and response framework. The
   following XML document shows a simple (hypothetical) natural language
   query. The name of the query element is FOO:natural-language-query,
   thus the type of the query is FOO:natural-language-query. The actual
   query is "Find the locations of good Thai restaurants in Los Angeles".
   For this hypothetical query, the arbiter returns two properties for
   each selected resource.SEARCH / HTTP/1.1
   Host: ryu.com
   Content-Type: text/xml
   Connection: Close
   Content-Length: 243

   <?xml version="1.0"?>
   <D:searchrequest xmlns:D = "DAV:" xmlns:F = "FOO:">
    <F:natural-language-query>
      Find the locations of good Thai restaurants in Los Angeles
    </F:natural-language-query>
   </D:searchrequest> >> ResponseHTTP/1.1 207 Multi-Status
   Content-Type: text/xml
   Content-Length: 333

   <?xml version="1.0"?>
   <D:multistatus xmlns:D="DAV:" xmlns:F="FOO:"
    xmlns:R="http://ryu.com/propschema">
    <D:response>
      <D:href>http://siamiam.com/</D:href>
      <D:propstat>
        <D:prop>
          <R:location>259 W. Hollywood</R:location>
          <R:rating><R:stars>4</R:stars></R:rating>
        </D:prop>
      </D:propstat>
    </D:response>
   </D:multistatus>




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 2.5 Unsuccessful Responses

   If an error occurred that prevented execution of the query, the server
   MUST indicate the failure with the appropriate status code and SHOULD
   include a DAV:multistatus element to point out errors associated with
   scopes.

   400 Bad Request. The query could not be executed. The request may be
   malformed (not valid XML for example). Additionally, this can be used
   for invalid scopes and search redirections.

   422 Unprocessable entity. The query could not be executed. If a
   text/xml request entity was provided, then it may have been valid
   (well-formed) but may have contained an unsupported or unimplemented
   query operator.

   507 (Insufficient Storage). The query produced more results than the
   server was willing to transmit. Partial results have been transmitted.
   The server MUST send a body that matches that for 207, except that
   there MAY exist resources that matched the search criteria for which
   no corresponding DAV:response exists in the reply.

2.5.1 Example: Result Set Truncation

   A server MAY limit the number of resources in a reply, for example to
   limit the amount of resources expended in processing a query. If it
   does so, the reply MUST use status code 507. It SHOULD include the
   partial results.

   When a result set is truncated, there may be many more resources that
   satisfy the search criteria but that were not examined.

   If partial results are included and the client requested an ordered
   result set in the original request, then any partial results that are
   returned MUST be ordered as the client directed.

   Note that the partial results returned MAY be any subset of the result
   set that would have satisfied the original query.SEARCH / HTTP/1.1
   Host: gdr.com
   Content-Type: text/xml
   Connection: Close
   Content-Length: xxxxx

   <?xml version="1.0"?>
   <D:searchrequest xmlns:D="DAV:">
    <D:basicsearch>
      à the query goes here à
    </D:basicsearch>
   </D:searchrequest>>> Response

   HTTP/1.1 507 Insufficient Storage
   Content-Type: text/xml

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   Content-Length: 738

   <?xml version="1.0"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
        <D:href>http://www.gdr.com/sounds/unbrokenchain.au</D:href>
        <D:propstat>
           <D:prop/>
           <D:status>HTTP/1.1 200 OK</D:status>
        </D:propstat>
     </D:response>
     <D:response>
        <D:href>http://tech.mit.edu/archive96/photos/Lesh1.jpg</D:href>
          <D:propstat>
             <D:prop/>
             <D:status>HTTP/1.1 200 OK</D:status>
          <D:/propstat>
     </D:response>
     <D:response>
       <D:href>http://gdr.com</href>
       <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
       <D:responsedescription>
          Only first two matching records were returned
       </D:responsedescription>
     </D:response>
   </D:multistatus>

2.6 Invalid Scopes & Search Redirections



2.6.1 Indicating an Invalid Scope

   A client may submit a scope that the arbiter may be unable to query.
   The inability to query may be due to network failure, administrative
   policy, security, etc. This raises the condition described as an
   "invalid scope".

   To indicate an invalid scope, the server MUST respond with a 400 (Bad
   Request).

   The response includes a text/xml body with a DAV:multistatus element.
   Each DAV:resource in the DAV:multistatus identifies a scope. To
   indicate that this scope is the source of the error, the server MUST
   include the DAV:scopeerror element.

2.6.2 Example of an Invalid Scope

   HTTP/1.1 400 Bad-Request
   Content-Type: text/xml
   Content-Length: xxxxx


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   <?xml version="1.0" ?>

   <d:multistatus xmlns:d="DAV:">
    <d:response>
      <d:href>http://www.foo.com/X</d:href>
        <d:status>HTTP/1.1 404 Object Not Found</d:status>
      <d:scopeerror/>
    </d:response>
   </d:multistatus>

2.6.3 Redirections

   As described above, a server can indicate only that the scope is
   invalid. Some search arbiters may be able to indicate that other
   search arbiters exist for that scope.

   In this case, the server MUST:

   (1) include the DAV:scopeerror element

   (2) include the DAV:status element for that scope. The value of this
   element MUST be a 303 (See Other) response.

   (3) include the DAV:redirectarbiter element for each arbiter the
   client should use for the redirect. The value of this element is the
   URI of the arbiter to use. Multiple DAV:redirectarbiter elements are
   allowed.

2.6.4 Example of a Search Redirection

   HTTP/1.1 400 Bad-Request
   Content-Type: text/xml
   Content-Length: xxxxx

   <?xml version="1.0" ?>
   <?xml:namespace ns="DAV:" prefix="d" ?>

   <d:multistatus>
    <d:response>
      <d:href>http://www.foo.com/X</d:href>
      <d:status>HTTP/1.1 303 See Other</d:status>
      <d:scopeerror/>
      <d:redirectarbiter>http://bar.com/B</d:redirectarbiter>
      <d:redirectarbiter>http://baz.com/B</d:redirectarbiter>
    </d:response>
   </d:multistatus>

2.6.5 Syntax for DAV:scopeerror

   <!ELEMENT scopeerror                    EMPTY>



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 2.6.6 Syntax for DAV:redirectarbiter

   <!ELEMENT redirectarbiter               (#PCDATA)> The contents must
   be a URL.

3. Discovery of Supported Query Grammars

   Servers MUST support discovery of the query grammars supported by a
   search arbiter resource.

   Clients can determine which query grammars are supported by an arbiter
   by invoking OPTIONS on the search arbiter. If the resource supports
   SEARCH, then the DASL response header will appear in the response. The
   DASL response header lists the supported grammars.

3.1 The OPTIONS Method

   The OPTIONS method allows the client to discover if a resource
   supports the SEARCH method and to determine the list of search
   grammars supported for that resource.

   The client issues the OPTIONS method against a resource named by the
   Request-URI. This is a normal invocation of OPTIONS defined in
   [RFC2068].

   If a resource supports the SEARCH method, then the server MUST list
   SEARCH in the OPTIONS response as defined by [RFC2068].

   DASL servers MUST include the DASL header in the OPTIONS response.
   This header identifies the search grammars supported by that resource.

3.2 The DASL Response Header

   DASLHeader = "DASL" ":" Coded-URL-List
   Coded-URL-List : Coded-URL [ "," Coded-URL-List ]
   Coded-URL ; defined in section 9.4 of [WEBDAV] The DASL response
   header indicates server support for a query grammar in the OPTIONS
   method. The value is a URI that indicates the type of grammar. This
   header MAY be repeated.

   For example:DASL: <http://foo.bar.com/syntax1>
   DASL: <http://akuma.com/syntax2>
   DASL: <FOO:natural-language-query>

3.3 Example: Grammar Discovery

   This example shows that the server supports search on the /somefolder
   resource with the query grammars: DAV:basicsearch,
   http://foo.bar.com/syntax1 and http://akuma.com/syntax2 . Note that
   every server MUST support DAV:basicsearch .



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   >>Request
   OPTIONS /somefolder HTTP/1.1
   Connection: Close
   Host: ryu.com >> ResponseHTTP/1.1 200 OK
   Date: Tue, 20 Jan 1998 20:52:29 GMT
   Connection: close
   Accept-Ranges: none
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE,
   MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, SEARCH
   Public: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE,
   MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, SEARCH
   DASL: <DAV:basicsearch>
   DASL: <http://foo.bar.com/syntax1>
   DASL: <http://akuma.com/syntax2>

4. Query Schema Discovery: QSD

   Servers MAY support the discovery of the schema for a query grammar.

   The DASL response header provides means for clients to discover the
   set of query grammars supported by a resource. This alone is not
   sufficient information for a client to generate a query. For example,
   the DAV:basicsearch grammar defines a set of queries consisting of a
   set of operators applied to a set of properties and values, but the
   grammar itself does not specify which properties may be used in the
   query. QSD for the DAV:basicsearch grammar allows a client to discover
   the set of properties that are searchable, selectable, and sortable.
   Moreover, although the DAV:basicsearch grammar defines a minimal set
   of operators, it is possible that a resource might support additional
   operators in a query. For example, a resource might support a optional
   operator that can be used to express content-based queries in a
   proprietary syntax. QSD allows a client to discover these operators
   and their syntax. The set of discoverable quantities will differ from
   grammar to grammar, but each grammar can define a means for a client
   to discover what can be discovered.

   In general, the schema for a given query grammar depends on both the
   resource (the arbiter) and the scope. A given resource might have
   access to one set of properties for one potential scope, and another
   set for a different scope. For example, consider a server able to
   search two distinct collections, one holding cooking recipes, the
   other design documents for nuclear weapons. While both collections
   might support properties such as author, title, and date, the first
   might also define properties such as calories and preparation time,
   while the second defined properties such as yield and applicable
   patents. Two distinct arbiters indexing the same collection might also
   have access to different properties. For example, the recipe
   collection mentioned above might also indexed by a value-added server
   that also stored the names of chefs who had tested the recipe. Note
   also that the available query schema might also depend on other
   factors, such as the identity of the principal conducting the search,
   but these factors are not exposed in this protocol.


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   Each query grammar supported by DASL defines its own syntax for
   expressing the possible query schema. A client retrieves the schema
   for a given query grammar on an arbiter resource with a given scope by
   invoking the SEARCH method on that arbiter, with that grammar and
   scope, with a query whose DAV:select element includes the
   DAV:queryschema property. This property is defined only in the context
   of such a search, a server SHOULD not treat it as defined in the
   context of a PROPFIND on the scope. The content of this property is an
   XML element whose name and syntax depend upon the grammar, and whose
   value may (and likely will) vary depending upon the grammar, arbiter,
   and scope.

   The query schema for DAV:basicsearch is defined in section 5.19.

4.1 The DAV:queryschema Property

   <!ELEMENT queryschema ANY >

4.1.1 Example of query schema discovery

   In this example, the arbiter is recipes.com, the grammar is
   DAV:basicsearch , the scope is also recipes.com.SEARCH / HTTP/1.1
   Host: recipes.com
   Content-Type: application/xml
   Connection: Close
   Content-Length: xxx

   <?xml version="1.0"?>
   <D:searchrequest xmlns:D="DAV:" >
    <D:basicsearch>
      <D:select>
         <D:queryschema/>
      </D:select>

   <D:from><D:scope><D:href>http://recipes.com</d:href></D:scope></D:from>
    </D:basicsearch>
   </D:searchrequest> Response:HTTP/1.1 207 Multistatus
   Content-Type: application/xml
   Content-Length: xxx

   <?xml version="1.0"?>
   <D:multistatus xmlns:D="DAV:">
    <D:response>
      <D:href>http://recipes.com</D:href>
      <D:propstat>
         <D:prop>
           <D:querygrammar>
             <D:basicsearchschema>
                 See section 5.19.9 for actual contents
             </D:basicsearchschema>
           </D:querygrammar>
         </D:prop>

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         <D:status>HTTP/1.1 200 Okay</D:status>
      </D:propstat>
    </D:response>
   </D:multistatus>

5 The DAV:basicsearch Grammar



5.1 Introduction

   DAV:basicsearch uses an extensible XML syntax that allows clients to
   express search requests that are generally useful for WebDAV
   scenarios. DASL-extended servers MUST accept this grammar, and MAY
   accept others grammars.

   DAV:basicsearch has several components:
     * DAV:select provides the result record definition.
     * DAV:from defines the scope.
     * DAV:where defines the criteria.
     * DAV:orderby defines the sort order of the result set.
     * DAV:limit provides constraints on the query as a whole.


































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5.2 The DAV:basicsearch DTD

   <!ELEMENT basicsearch   (select, from, where?, orderby?, limit?) >

   <!ELEMENT select        (allprop | prop) >

   <!ELEMENT from  (scope) >
   <!ELEMENT scope (href, depth?) ><!ENTITY %comp_ops      "eq | lt | gt|
   lte | gte">
   <!ENTITY %log_ops       "and | or | not">
   <!ENTITY %special_ops   "isdefined">
   <!ENTITY %string_ops    "like">
   <!ENTITY %content_ops   "contains">

   <!ENTITY %all_ops       "%comp_ops; | %log_ops; | %special_ops;
   |%string_ops; | %content_ops;"><!ELEMENT where ( %all_ops; ) >

   <!ELEMENT and   ( ( %all_ops; ) +) >

   <!ELEMENT or    ( ( %all_ops; ) +) >

   <!ELEMENT not   ( %all_ops; ) >

   <!ELEMENT lt    ( prop , literal ) >
   <!ATTLIST lt    casesensitive   (1|0) "1" >

   <!ELEMENT lte   ( prop , literal ) >
   <!ATTLIST lte   casesensitive   (1|0) "1" >

   <!ELEMENT gt    ( prop , literal) >
   <!ATTLIST gt    casesensitive   (1|0) "1" >

   <!ELEMENT gte   ( prop , literal ) >
   <!ATTLIST gte   casesensitive   (1|0) "1" >

   <!ELEMENT eq    ( prop , literal ) >
   <!ATTLIST eq    casesensitive   (1|0) "1" >

   <!ELEMENT literal       (#PCDATA)>
   <!ATTLIST literal       xml:space       (default|preserve) preserve >

   <!ELEMENT isdefined     (prop) >
   <!ELEMENT like  (prop, literal) >
   <!ELEMENT contains      (#PCDATA)>

   <!ELEMENT orderby       (order+) >
   <!ELEMENT order (prop, (ascending | descending)?)

   <!ATTLIST order casesensitive   (1|0) "1" >
   <!ELEMENT ascending     EMPTY>
   <!ELEMENT descending    EMPTY>

   <!ELEMENT limit (nresults) >
   <!ELEMENT nresults      (#PCDATA) >


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5.2.1 Example Query

   This query retrieves the content length values for all resources
   located under the server's "/container1/" URI namespace whose length
   exceeds 10000.<d:searchrequest>
    <d:basicsearch>
      <d:select>
        <d:prop><d:getcontentlength/></d:prop>
      </d:select>
      <d:from>
        <d:scope>
          <d:href>/container1/</d:href>
          <d:depth>infinity</d:depth>
        </d:scope>
      </d:from>
      <d:where>
        <d:gt>
          <d:prop><d:getcontentlength/></d:prop>
          <d:literal>10000</d:literal>
        </d:gt>
      </d:where>
        <d:orderby>
          <d:order>
          <d:prop><d:getcontentlength/><d:prop>
          <d:ascending/>
        </d:order>
      </d:orderby>
    </d:basicsearch>
   </d:searchrequest>

5.3 DAV:select

   DAV:select defines the result record, which is a set of properties and
   values. This document defines two possible values: DAV:allprop and
   DAV:prop , both defined in [WebDAV].

   If the value is DAV:allprop , the result record for a given resource
   includes all the properties for that resource.

   If the value is DAV:prop , then the result record for a given resource
   includes only those properties named by the DAV:prop element. Each
   property named by the DAV:prop element must be referenced in the
   Multistatus response.




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The rules governing the status codes for each property match those of
   the PROPFIND method defined in [WebDAV].

5.4 DAV:from

   DAV:from defines the query scope. This contains exactly one DAV:scope
   element. The scope element contains a mandatory DAV:href element and
   an optional DAV:depth element.

   DAV:href indicates the URI for a collection to use as a scope.

   When the scope is a collection, if DAV:depth is "0", the search
   includes only the collection. When it is "1", the search includes the
   (toplevel) members of the collection. When it is "infinity", the
   search includes all recursive members of the collection.

5.4.1 Relationship to the Request-URI

   If the DAV:scope element is an absolute URI, the scope is exactly that
   URI.

   If the DAV:scope element is a relative URI, the scope is taken to be
   relative to the request-URI.

5.4.2 Scope

   A Scope can be an arbitrary URI.

   Servers, of course, may support only particular scopes. This may
   include limitations for particular schemes such as "http:" or "ftp:"
   or certain URI namespaces.

   If a scope is given that is not supported the server MUST respond with
   a 400 status code that includes a Multistatus error. A scope in the
   query appears as a resource in the response and must include an
   appropriate status code indicating its validity with respect to the
   search arbiter.

   Example:HTTP/1.1 400 Bad Request
   Content-Type: text/xml
   Content-Length: 428

   <?xml version="1.0" ?>
   <d:multistatus xmlns:D="DAV:" xmlns:F="FOO:" >
    <d:response>
      <d:href>http://www.foo.com/scope1</d:href>
      <d:status>HTTP/1.1 502 Bad Gateway</d:status>
    </d:response>
   </d:multistatus> This example shows the response if there is a scope
   error. The response provides a Multistatus with a status for the
   scope. In this case, the scope cannot be reached because the server
   cannot search another server (502).

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 5.5 DAV:where

   DAV:where element defines the search condition for inclusion of
   resources in the result set. The value of this element is an XML
   element that defines a search operator that evaluates to one of the
   Boolean truth values TRUE, FALSE, or UNKNOWN. The search operator
   contained by DAV:where may itself contain and evaluate additional
   search operators as operands, which in turn may contain and evaluate
   additional search operators as operands, etc. recursively.

5.5.1 Use of Three-Valued Logic in Queries

   Each operator defined for use in the where clause that returns a
   Boolean value MUST evaluate to TRUE, FALSE, or UNKNOWN. The resource
   under scan is included as a member of the result set if and only if
   the search condition evaluates to TRUE.

   Consult Appendix A for details on the application of three-valued
   logic in query expressions.

5.5.2 Handling Optional operators

   If a query provides an operator that is not supported by the server,
   then the server MUST respond with a 422 (Unprocessable Entity) status
   code.

5.5.3 Treatment of NULL Values

   If a SEARCH PROPFIND for a property value would yield a 404 or 403
   response for that property, then that property is considered NULL.

   NULL values are "less than" all other values in comparisons.

   Empty strings (zero length strings) are not NULL values. An empty
   string is "less then" a string with length greater than zero.

   The DAV:isdefined operator is defined to test if the value of a
   property is NULL.

5.5.4 Example: Testing for Equality

   The example shows a single operator ( DAV:eq ) applied in the
   criteria.<d:where>
    <d:eq>
      <d:prop> <d:getcontentlength/> </d:prop>
      <d:literal> 100 </d:literal>
    </d:eq>

   </d:where>




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5.5.5 Example: Relative Comparisons

   The example shows a more complex operation involving several operators
   ( DAV:and , DAV:eq , DAV:gt ) applied in the criteria. This DAV:where
   expression matches those resources that are "image/gifs" over 4K in
   size.<D:where>
    <D:and>
      <D:eq>
        <D:prop> <D:getcontenttype/> </D:prop>
        <D:literal> image/gif </D:literal>
      </D:eq>
      <D:gt>
        <D:prop> <D:getcontentlength/> </D:prop>
        <D:literal> 4096 </D:literal>
      </D:gt>
    </D:and>

   </D:where>

5.6 DAV:orderby

   The DAV:orderby element specifies the ordering of the result set. It
   contains one or more DAV:order elements, each of which specifies a
   comparison between two items in the result set. Informally, a
   comparison specifies a test that determines whether one resource
   appears before another in the result set. Comparisons are applied in
   the order they occur in the DAV:orderby element, earlier comparisons
   being more significant.

   The comparisons defined here use only a single property from each
   resource, compared using the same ordering as the DAV:lt operator
   (ascending) or DAV:gt operator (descending). If neither direction is
   specified, the default is DAV:ascending .

   In the context of the DAV:orderby element, null values are considered
   to collate before any actual (i.e., non null) value, including strings
   of zero length (as in ANSI standard SQL, [ANSISQL]).

5.6.1 Comparing Natural Language Strings.

   Comparisons on strings take into account the language defined for that
   property. Clients MAY specify the language using the xml:lang
   attribute. If no language is specified either by the client or defined
   for that property by the server or if a comparison is performed on
   strings of two different languages, the results are undefined.

   The DAV:casesensitive attribute may be used to indicate
   case-sensitivity for comparisons.





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 5.6.2 Example of Sorting

   This sort orders first by last name of the author, and then by size,
   in descending order, so that the largest works appear first.
   <d:orderby>
    <d:order>
      <d:prop><r:lastname/></d:prop>
      <d:ascending/>
    </d:order>
    <d:order>
      <d:prop><d:getcontentlength/></d:prop>
      <d:descending/>
    </d:order>
   </d:orderby>

5.7 Boolean Operators: DAV:and , DAV:or , and DAV:not

   The DAV:and operator performs a logical AND operation on the
   expressions it contains.

   The DAV:or operator performs a logical OR operation on the values it
   contains.

   The DAV:not operator performs a logical NOT operation on the values it
   contains.

5.8 DAV:eq

   The DAV:eq operator provides simple equality matching on property
   values.

   The DAV:casesensitive attribute may be used with this element.

5.9 DAV:lt , DAV:lte , DAV:gt , DAV:gte

   The DAV:lt , DAV:lte , DAV:gt , and DAV:gte operators provide
   comparisons on property values, using less-than, less-than or equal,
   greater-than, and greater-than or equal respectively. The
   DAV:casesensitive attribute may be used with these elements.

5.10 DAV:literal

   DAV:literal allows literal values to be placed in an expression.

   Because white space in literal values is significant in comparisons,
   DAV:literal makes use of the xml:space attribute to identify this
   significance. The default value of this attribute for DAV:literal is
   preserve. Consult section 2.10 of [XML] for more information on the
   use of this attribute.




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5.11 DAV:isdefined

   The DAV:isdefined operator allows clients to determine whether a
   property is defined on a resource. The meaning of "defined on a
   resource" is found in section 5.5.3.

   Example:
   <d:isdefined>
     <d:prop><x:someprop/></d:prop>
   </d:isdefined>

    The DAV:isdefined operator is optional.

5.12 DAV:like

   The DAV:like is an optional operator intended to give simple
   wildcard-based pattern matching ability to clients.

   The operator takes two arguments.

   The first argument is a DAV:prop element identifying a single property
   to evaluate.

   The second argument is a DAV:literal element that gives the pattern
   matching string.

5.12.1 Syntax for the Literal Pattern

   Pattern := [wildcard] 0*( text [wildcard] )
   wildcard := exactlyone | zeroormore
   text := 1*( <octet> | escapesequence )
   exactlyone : = "?"
   zeroormore := "%"
   escapechar := "\"
   escapesequence := "\" ( exactlyone | zeroormore | escapechar ) The
   value for the literal is composed of wildcards separated by segments
   of text. Wildcards may begin or end the literal. Wildcards may not be
   adjacent.

   The "?" wildcard matches exactly one character.

   The "%" wildcard matches zero or more characters

   The "\" character is an escape sequence so that the literal can
   include "?" and "%". To include the "\" character in the pattern, the
   escape sequence "\\" is used..

5.12.2 Example of DAV:like

   This example shows how a client might use DAV:like to identify those
   resources whose content type was a subtype of image.<D:where>
    <D:like>
      <D:prop><D:getcontenttype/></D:prop>
      <D:literal>image%</D:literal>
    </D:like>

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   </D:where>

5.13 DAV:contains

   The DAV:contains operator is an optional operator that provides
   content-based search capability. This operator implicitly searches
   against the text content of a resource, not against content of
   properties. The DAV:contains operator is intentionally not overly
   constrained, in order to allow the server to do the best job it can in
   performing the search.

   The DAV:contains operator evaluates to a Boolean value. It evaluates
   to TRUE if the content of the resource satisfies the search.
   Otherwise, It evaluates to FALSE.

   Within the DAV:contains XML element, the client provides a phrase: a
   single word or whitespace delimited sequence of words. Servers MAY
   ignore punctuation in a phrase. Case-sensitivity is left to the
   server.

   The following things may or may not be done as part of the search:
   Phonetic methods such as "soundex" may or may not be used. Word
   stemming may or may not be performed. Thesaurus expansion of words may
   or may not be done. Right or left truncation may or may not be
   performed. The search may be case insensitive or case sensitive. The
   word or words may or may not be interpreted as names. Multiple words
   may or may not be required to be adjacent or "near" each other.
   Multiple words may or may not be required to occur in the same order.
   Multiple words may or may not be treated as a phrase. The search may
   or may not be interpreted as a request to find documents "similar" to
   the string operand.

   The DAV:score property is intended to be useful to rank documents
   satisfying the DAV:contains operator.

5.13.1 Examples

   The example below shows a search for the phrase "Peter Forsberg".

   Depending on its support for content-based searching, a server MAY
   treat this as a search for documents that contain the words "Peter"
   and "Forsberg".<D:where>
    <D:contains>Peter Forsberg</D:contains>
   </D:where> The example below shows a search for resources that contain
   "Peter" and "Forsberg".<D:where>
    <D:and>
      <D:contains>Peter</D:contains>
      <D:contains>Forsberg</D:contains>
    </D:and>
   </D:where>



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 5.14 The DAV:limit XML Element

   <!ELEMENT limit (nresults) > The DAV:limit XML element contains
   requested limits from the client to limit the size of the reply or
   amount of effort expended by the server.

5.15 The DAV:nresults XML Element

   <!ELEMENT nresults (#PCDATA)> ;only digits The DAV:nresults XML
   element contains a requested maximum number of records to be returned
   in a reply. The server MAY disregard this limit. The value of this
   element is an integer.

5.16 The DAV:casesensitive XML attribute

   The DAV:casesensitive attribute allows clients to specify
   case-sensitive or case-insensitive behavior for DAV:basicsearch
   operators.

   The possible values for DAV:casesensitive are "1" or "0". The "1"
   value indicates case-sensitivity. The "0" value indicates
   case-insensitivity. The default value is server-specified.

   Support for the DAV:casesensitive is optional. A server should respond
   with an error 422 if the DAV:casesensitive attribute is used but
   cannot be supported.

5.17 The DAV:score Property

   <!ELEMENT score (#PCDATA)> The DAV:score XML element is a synthetic
   property whose value is defined only in the context of a query result
   where the server computes a score, e.g. based on relevance. It may be
   used in DAV:select or DAV:orderby elements. Servers SHOULD support
   this property. The value is a string representing the score, an
   integer from zero to 10000 inclusive, where a higher value indicates a
   higher score (e.g. more relevant).

   Clients should note that, in general, it is not meaningful to compare
   the numeric values of scores from two different queries unless both
   were executed by the same underlying search system on the same
   collection of resources.

5.18 The DAV:iscollection Property

   <!ELEMENT iscollection  (#PCDATA)> The DAV:iscollection XML element is
   a synthetic property whose value is defined only in the context of a
   query.






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                                 DASL

   The property is TRUE (the literal string "1") of a resource if and only
   if a PROPFIND of the DAV:resourcetype property for that resource would
   contain the DAV:collection XML element. The property is FALSE (the
   literal string "0") otherwise.

   Rationale : This property is provided in lieu of defining generic
   structure queries, which would suffice for this and for many more
   powerful queries, but seems inappropriate to standardize at this time.

5.18.1 Example of DAV:iscollection

   This example shows a search criterion that picks out all and only the
   resources in the scope that are collections.<D:where>
    <D:eq>
      <D:prop><D:iscollection></D:prop>
      <D:literal>1<D:literal>
    </D:eq>
   </D:where>

5.19 QuerySchema for DAV:basicsearch

   The DAV:basicsearch grammar defines a search criteria that is a
   Boolean-valued expression, and allows for an arbitrary set of
   properties to be included in the result record. The result set may be
   sorted on a set of property values. Accordingly the DTD for schema
   discovery for this grammar allows the server to express:
     1 the set of optional operators defined by the resource.

5.19.1 DTD for DAV:basicsearch QSD

   <!ELEMENT basicsearchschema  (properties, operators)>
   <!ELEMENT properties    (propdesc*)>
   <!ELEMENT propdesc    (prop, ANY)>
   <!ELEMENT operators    (opdesc*)>
   <!ELEMENT opdesc        ANY>
   <!ELEMENT operand_property      EMPTY>
   <!ELEMENT operand_literal       EMPTY> The DAV:properties element
   holds a list of descriptions of properties.

   The DAV:operators element describes the optional operators that may be
   used in a DAV:where element.

5.19.2 DAV:propdesc Element

   Each instance of a DAV:propdesc element describes the property or
   properties in the DAV:prop element it contains. All subsequent
   elements are descriptions that apply to those properties. All
   descriptions are optional and may appear in any order. Servers SHOULD
   support all the descriptions defined here, and MAY define others.




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   DASL defines five descriptions. The first, DAV:datatype , provides a
   hint about the type of the property value, and may be useful to a user
   interface prompting for a value. The remaining four ( DAV:searchable ,
   DAV:selectable , DAV:sortable , and DAV:casesensitive ) identify
   portions of the query ( DAV:where , DAV:select , and DAV:orderby ,
   respectively). If a property has a description for a section, then the
   server MUST allow the property to be used in that section. These
   descriptions are optional. If a property does not have such a
   description, or is not described at all, then the server MAY still
   allow the property to be used in the corresponding section.

5.19.3 The DAV:datatype Property Description

   The DAV:datatype element contains a single XML element that provides a
   hint about the domain of the property, which may be useful to a user
   interface prompting for a value to be used in a query. The namespace
   for expressing a DASL defined data type is
   "urn:uuid:C2F41010-65B3-11d1-A29F-00AA00C14882/".<!ELEMENT datatype
   ANY > DASL defines the following data type elements: Name example
   boolean 1, 0
   string Foobar
   dateTime.iso8601tz 1994-11-05T08:15:5Z
   float .314159265358979E+1
   int -259, 23


   If the data type of a property is not given, then the data type
   defaults to string.

5.19.4 The DAV:searchable Property Description

   <!ELEMENT searchable                    EMPTY > If this element is
   present, then the server MUST allow this property to appear within a
   DAV:where element where an operator allows a property. Allowing a
   search does not mean that the property is guaranteed to be defined on
   every resource in the scope, it only indicates the server's
   willingness to check.

5.19.5 The DAV:selectable Property Description

   <!ELEMENT selectable                    EMPTY > This element indicates
   that the property may appear in the DAV:select element.

5.19.6 The DAV:sortable Property Description

   This element indicates that the property may appear in the DAV:orderby
   element<!ELEMENT sortable                              EMPTY >






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 5.19.7 The DAV:casesensitive Property Description

   This element only applies to properties whose data type is "string" as
   per the DAV:datatype property description. Its presence indicates that
   compares performed for searches, and the comparisons for ordering
   results on the string property will be case sensitive. (The default is
   case insensitive.)<!ELEMENT casesensitive EMPTY >

5.19.8 The DAV:operators XML Element

   The DAV:operators element describes every optional operator supported
   in a query. (Mandatory operators are not listed since they are
   mandatory and permit no variation in syntax.). All optional operators
   that are supported MUST be listed in the DAV:operators element. The
   listing for an operator consists of the operator (as an empty
   element), followed by one element for each operand. The operand MUST
   be either DAV:operand _property or DAV:operand _literal, which
   indicate that the operand in the corresponding position is a property
   or a literal value, respectively. If an operator is polymorphic
   (allows more than one operand syntax) then each permitted syntax MUST
   be listed separately.
   <D:propdesc><D:like/><D:operand_property/><D:operand_literal/></D:propdesc>

5.19.9 Example of Query Schema for DAV:basicsearch

   <D:basicsearchschema xmlns:D="DAV:"
   xmlns:t="urn:uuid:C2F41010-65B3-11d1-A29F-00AA00C14882/"
   xmlns:J="http://jennicam.org">
    <D:properties>
      <D:propdesc>
        <D:prop><D:getcontentlength/></D:prop>
        <D:datatype><t:int></D:datatype>
        <D:searchable/><D:selectable/><D:sortable/>
      </D:propdesc>
      <D:propdesc>
        <D:prop><D:getcontenttype/><D:displayname></D:prop>
        <D:searchable/><D:selectable/> <D:sortable/>
      </D:propdesc>
      <D:propdesc>
        <D:prop><J:fstop/></D:prop>
        <D:selectable/>
      </D:propdesc>
    </D:properties>
    <D:operators>
      <D:opdesc>
      <D:isdefined/><D:operand_property/>
    </D:opdesc>
     <D:opdesc>
      <D:like/><D:operand_property/><D:operand_literal/>
    </D:opdesc>
    </D:operators>
   </D:basicsearchschema> This response lists four properties. The

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   datatype of the last three properties is not given, so it defaults to
   string. All are selectable, and the first three may be searched. All
   but the last may be used in a sort. Of the optional DAV operators,
   DAV:isdefined and DAV:like are supported.

   Note: The schema discovery defined here does not provide for discovery
   of supported values of the DAV:casesensitive attribute. This may
   require that the reply also list the mandatory operators.

6 Internationalization Considerations

   Clients have the opportunity to tag properties when they are stored in
   a language. The server SHOULD read this language-tagging by examining
   the xml:lang attribute on any properties stored on a resource.

   The xml:lang attribute specifies a nationalized collation sequence
   when properties are compared.

   Comparisons when this attribute differs have undefined order.

7 Security Considerations

   This section is provided to detail issues concerning security
   implications of which DASL applications need to be aware. All of the
   security considerations of HTTP/1.1 also apply to DASL. In addition,
   this section will include security risks inherent in searching and
   retrieval of resource properties and content.

   A query must not allow one to retrieve information about values or
   existence of properties that one could not obtain via PROPFIND. (e.g.
   by use in DAV:orderby , or in expressions on properties.)

   A server should prepare for denial of service attacks. For example a
   client may issue a query for which the result set is expensive to
   calculate or transmit because many resources match or must be
   evaluated. 7.1 Implications of XML External Entities

   XML supports a facility known as "external entities", defined in
   section 4.2.2 of [REC-XML], which instruct an XML processor to
   retrieve and perform an inline include of XML located at a particular
   URI. An external XML entity can be used to append or modify the
   document type declaration (DTD) associated with an XML document. An
   external XML entity can also be used to include XML within the content
   of an XML document. For non-validating XML, such as the XML used in
   this specification, including an external XML entity is not required
   by [REC-XML]. However, [REC-XML] does state that an XML processor may,
   at its discretion, include the external XML entity.






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   External XML entities have no inherent trustworthiness and are subject
   to all the attacks that are endemic to any HTTP GET request.
   Furthermore, it is possible for an external XML entity to modify the
   DTD, and hence affect the final form of an XML document, in the worst
   case significantly modifying its semantics, or exposing the XML
   processor to the security risks discussed in [RFC2376]. Therefore,
   implementers must be aware that external XML entities should be
   treated as untrustworthy.

   There is also the scalability risk that would accompany a widely
   deployed application which made use of external XML entities. In this
   situation, it is possible that there would be significant numbers of
   requests for one external XML entity, potentially overloading any
   server which fields requests for the resource containing the external
   XML entity.

8 Scalability

   Query grammars are identified by URIs. Applications SHOULD not attempt
   to retrieve these URIs even if they appear to be retrievable (for
   example, those that begin with "http://")

9 Authentication

   Authentication mechanisms defined in WebDAV will also apply to DASL.

10 IANA Considerations

   This document uses the namespace defined by [WebDAV] for XML elements.
   All other IANA considerations mentioned in [WebDAV] also applicable to
   DASL

11 Copyright

   To be supplied.

12 Intellectual Property

   To be supplied.

13 References



13.1 Normative References

   [DASLREQ] J. Davis, S. Reddy, J. Slein, "Requirements for DAV
   Searching and Locating", Feb 24, 1999, internet-draft,
   work-in-progress, draft-dasl-requirements-01.txt




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                                 DASL


   [RFC2068] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, and T.
   Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, U.C.
   Irvine, DEC, MIT/LCS, January 1997.

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
   Requirement Levels." RFC 2119, BCP 14. Harvard University. March,
   1997.

   [RFC2376] E. Whitehead, M. Murata, "XML Media Types". RFC 2376, July
   1998.

   [WebDAV] Y. Goland, E.J. Whitehead, A. Faizi, S.R. Carter, D. Jenson,
   "HTTP Extensions for Distributed Authoring -- WebDAV", RFC 2518,
   February 1999.

   [XML] T. Bray, J. Paoli, C. M. Sperberg-McQueen, "Extensible Markup
   Language (XML) 1.0", September 16, 1998, W3C Recommendation.

   [XMLNS] T. Bray, D. Hollander, A. Layman, "Namespaces in XML",
   14-January-1999, W3C Recommendation.
   http://www.w3.org/TR/REC-xml-names/ .

13.2 Non-Normative References

   [ANSISQL] ANSI, "Information Systems - Database Language - SQL
   (includes ANSI X3.168-1989)", ANSI X3.135-1992 (R1998), 1992.

14 Author's Addresses

   Saveen Reddy
   Microsoft
   One Microsoft Way
   Redmond WA, 9085-6933
   Email:saveenr@microsoft.com

   Dale Lowry
   Novell
   1555 N. Technology Way
   M/S ORM-M-314
   Orem, UT  84097
   Email: dlowry@novell.com


   Surendra Reddy
   Oracle Corporation
   600 Oracle Parkway, M/S 6op3,
   Redwoodshores, CA 94065
   Email: skreddy@us.oracle.com
   Phone:(650) 506 5441

   Rick Henderson
   Netscape

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                                 DASL


   Email: rickh@netscape.com

   Jim Davis
   CourseNet Systems
   San Francisco, CA
   Email: jrd3@alum.mit.edu

   Alan Babich
   Filenet
   3565 Harbor Blvd.
   Costa Mesa, CA 92626
   714-966-3403
   Email: ababich@filenet.com

15 APPENDICES



Three-Valued Logic in DAV:basicsearch

   ANSI standard three valued logic is used when evaluating the search
   condition (as defined in the ANSI standard SQL specifications, for
   example in ANSI X3.135-1992, section 8.12, pp. 188-189, section 8.2,
   p. 169, General Rule 1)a), etc.).

   ANSI standard three valued logic is undoubtedly the most widely
   practiced method of dealing with the issues of properties in the
   search condition not having a value (e.g., being null or not defined)
   for the resource under scan, and with undefined expressions in the
   search condition (e.g., division by zero, etc.). Three valued logic
   works as follows.

   Undefined expressions are expressions for which the value of the
   expression is not defined. Undefined expressions are a completely
   separate concept from the truth value UNKNOWN, which is, in fact, well
   defined. Property names and literal constants are considered
   expressions for purposes of this section. If a property in the current
   resource under scan has not been set to a value (either because the
   property is not defined for the current resource, or because it is
   null for the current resource), then the value of that property is
   undefined for the resource under scan. DASL 1.0 has no arithmetic
   division operator, but if it did, division by zero would be an
   undefined arithmetic expression.

   If any subpart of an arithmetic, string, or datetime subexpression is
   undefined, the whole arithmetic, string, or datetime subexpression is
   undefined.






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   There are no manifest constants to explicitly represent undefined
   number, string, or datetime values.

   Since a Boolean value is ultimately returned by the search condition,
   arithmetic, string, and datetime expressions are always arguments to
   other operators. Examples of operators that convert arithmetic,
   string, and datetime expressions to Boolean values are the six
   relational operators ("greater than", "less than", "equals", etc.). If
   either or both operands of a relational operator have undefined
   values, then the relational operator evaluates to UNKNOWN. Otherwise,
   the relational operator evaluates to TRUE or FALSE, depending upon the
   outcome of the comparison.

   The Boolean operators DAV:and , DAV:or and DAV:not are evaluated
   according to the following rules:

   UNKNOWN and UNKNOWN = UNKNOWN

   UNKNOWN or UNKKNOWN = UNKNOWN

   not UNKNOWN = UNKNOWN

   UNKNOWN and TRUE = UNKNOWN

   UNKNOWN and FALSE = FALSE

   UNKNOWN and UNKNOWN = UNKNOWN

   UNKNOWN or TRUE = TRUE

   UNKNOWN or FALSE = UNKNOWN

   UNKNOWN or UNKNOWN = UNKNOWN

16 Change History



   Feb 14, 1998
       Initial Draft
   Feb 28, 1998
       Referring to DASL as an extension to HTTP/1.1 rather than DAV

   Added new sections "Notational Conventions", "Protocol Model",
   "Security Considerations"
   Changed section 3 to "Elements of Protocol"
   Added some stuff to introduction
   Added "result set" terminology
   Added "IANA Considerations".
   Mar 9, 1998
       Moved sub-headings of "Elements of Protocol" to first level and
       removed "Elements of Protocol" Heading.

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                                 DASL



   Added an sentence in introduction explaining that this is a "sketch"
   of a protocol.
   Mar 11, 1998
       Added orderby, data typing, three valued logic, query schema
       property, and element definitions for schema for basicsearch.
   April 8, 1998
       - made changes based on last weekÆs DASL BOF.
   May 8, 1998
       Removed most of DAV:searcherror ; converted to DAV:searchredirect

   Altered DAV:basicsearch grammar to use avoid use of ANY in DTD
   June 17, 1998
       -Added details on Query Schema Discovery

   -Shortened list of data types
   June 23, 1998
       moved data types before change history

   rewrote the data types section
   removed the casesensitive element and replace with the casesensitive
   attribute
   added the casesensitive attribute to the DTD for all operations that
   might work on a string
   Jul 20, 1998
       A series of changes. See AuthorÆs meeting minutes for details.
   July 28, 1998
       Changes as per author's meeting. QSD uses SEARCH, not PROPFIND.

   Moved text around to keep concepts nearby.
   Boolean literals are 1 and 0, not T and F.
   contains changed to contentspassthrough.
   Renamed rank to score.
   July 28, 1998
       Added Dale Lowry as Author
   September 4, 1998
       Added 422 as response when query lists unimplemented operators.

   DAV:literal declares a default value for xml:space, 'preserve' (see
   XML spec, section 2.10)
   moved to new XML namespace syntax
   September 22, 1998
       Changed "simplesearch" to "basicsearch"

   Changed isnull to isdefined
   Defined NULLness as having a 404 or 403 response
   used ENTITY syntax in DTD
   Added redirect
   October 9, 1998
       Fixed a series of typographical and formatting errors.

   Modified the section of three-valued logic to use a table rather than

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                                 DASL


   a text description of the role of UNKNOWN in expressions.
   November 2, 1998
       Added the DAV:contains operator.

   Removed the DAV:contentpassthrough operator.
   November 18, 1998
       Various author comments for submission
   June 3, 1999
       Cosmetic and minor editorial changes only. Fix nits reported by
       Jim Whitehead in email of April 26, 1999. Converted to HTML from
       Word 97, manually.

Reddy et al        Expires December 24 1999                   [Page 30]


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