[Search] [pdf|bibtex] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 02 03 04                                                   
       INTERNET-DRAFT                         Saveen Reddy, Microsoft
       draft-reddy-dasl-protocol-02.txt       Del Jensen, Novell
                                               Surendra Reddy, Oracle
                                               Rick Henderson, Netscape
                                               Jim Davis, Xerox
                                               Alan Babich, Filenet
  
       Expires Jan 28, 1999                   July 28, 1998
  
  
                          DAV Searching & Locating
  
  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 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".
  
       To learn the current status of any Internet draft please check the
       "lid-abstracts.txt" listing contained in the Internet drafts shadow
       directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
       munnari.oz.au (Pacific Rim), ftp.isi.edu (US East coast) or
       ftp.isi.edu (US West coast).  Further information about the IETF
       can be found at URL: http://www.ietf.org/
  
       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.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  Reddy, et al                                        [Page 1]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
                              Table of Contents
  
  
  DAV SEARCHING & LOCATING..................................1
  
  
  TABLE OF CONTENTS.........................................2
  
  
  1.  INTRODUCTION..........................................4
  1.1. DASL................................................4
  1.2. Relationship to DAV.................................4
  1.3. Terms...............................................4
  1.4. Notational Conventions..............................4
  1.5. An Overview of DASL at Work.........................5
  
  
  2.  THE SEARCH METHOD.....................................5
  2.1. Overview............................................5
  2.2. The Request.........................................5
   2.2.1.The Request-URI...................................5
   2.2.2.The Request Body..................................5
  2.3. The DAV:searchrequest XML Element...................6
  2.4. The Successful 207 (Multistatus) Response...........6
   2.4.1.Etxending the PROPFIND Response...................6
   2.4.2.Example: A Simple Request and Response............6
  2.5. Unsuccessful Responses..............................7
   2.5.1.Example: Result Set Truncation....................8
  
  
  3.  DISCOVERY OF SUPPORTED QUERY GRAMMARS.................9
  3.1. The OPTIONS Method..................................9
  3.2. The DASL Response Header............................9
  3.3. Example: Grammar Discovery..........................9
  
  
  4.  QUERY SCHEMA DISCOVERY: QSD..........................10
  4.1. The DAV:queryschema Property.......................11
   4.1.1.Example of query schema discovery................11
  
  
  5.  THE DAV:SIMPLESEARCH GRAMMAR.........................12
  5.1. Introduction.......................................12
  5.2. The DAV:simplesearch DTD...........................12
   5.2.1.Example query....................................13
  5.3. DAV:select.........................................14
  5.4. DAV:from...........................................14
   5.4.1.Relationship to the Request-URI..................14
   5.4.2.Scope............................................14
  5.5. DAV:where..........................................15
   5.5.1.Use of Three-Valued Logic in Queries.............15
   5.5.2.Handling Optional operators......................15
   5.5.3.Treatment of NULL Values.........................16
   5.5.4.Example: Testing for Equality....................16
   5.5.5.Example: Relative Comparisons....................16
  5.6. DAV:sortby.........................................16
   5.6.1.Comparing Natural Language Strings...............17
  
  
  Reddy, et al                                        [Page 2]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
   5.6.2.Example of Sorting...............................17
  5.7. Boolean Operators: DAV:and, DAV:or, and DAV:not....17
  5.8. DAV:eq.............................................18
  5.9. DAV:lt, DAV:lte, DAV:gt, DAV:gte...................18
  5.10.DAV:literal........................................18
  5.11.DAV:isnull.........................................18
  5.12.DAV:like...........................................18
   5.12.1.  Syntax for the Literal Pattern................18
   5.12.2.  Example of DAV:like...........................19
  5.13.DAV:contentpassthrough.............................19
  5.14.The DAV:limit XML Element..........................19
  5.15.The DAV:nresults XML Element.......................19
  5.16.The DAV:casesensitive XML attribute................20
  5.17.The DAV:score Property.............................20
  5.18.The DAV:iscollection Property......................20
   5.18.1.  Exampe of DAV:iscollection....................21
  5.19.Query Schema for DAV:simplesearch..................21
   5.19.1.  DTD for DAV:simplesearch QSD..................21
   5.19.2.  DAV:propdesc Element..........................21
   5.19.3.  The DAV:datatype Property Description.........22
   5.19.4.  The DAV:searchable Property Description.......22
   5.19.5.  The DAV:selectable Property Description.......22
   5.19.6.  The DAV:sortable Property Description.........23
   5.19.7.  The DAV:operators XML Element.................23
   5.19.8.  Example of Query Schema for DAV:simplesearch..23
  
  
  6.  INTERNATIONALIZATION CONSIDERATIONS..................24
  
  
  7.  SECURITY CONSIDERATIONS..............................24
  
  
  8.  SCALABILITY..........................................24
  
  
  9.  AUTHENTICATION.......................................24
  
  
  10.  IANA CONSIDERATIONS................................25
  
  
  11.  COPYRIGHT..........................................25
  
  
  12.  INTELLECTUAL PROPERTY..............................25
  
  
  13.  REFERENCES.........................................25
  
  
  14.  AUTHOR'S ADDRESSES.................................25
  
  
  15.  APPENDICES.........................................26
  Appendix A  Three-Valued Logic in DAV:simplesearch......26
  Appendix B  Change History..............................27
   Feb 14, 1998............................................27
   Feb 28, 1998............................................27
  
  
  Reddy, et al                                        [Page 3]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
   Mar 9, 1998.............................................28
   Mar 11, 1998............................................28
   April 8, 1998...........................................28
   May 8, 1998.............................................28
   June 17, 1998...........................................28
   June 23, 1998...........................................28
   Jul 20, 1998............................................28
   July 28, 1998...........................................28
   July 28, 1998...........................................29
  
  
  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.
  
       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:simplesearch XML element and query grammar, and
  
       - the DAV:simplesearchschema 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
  
  
  
  Reddy, et al                                        [Page 4]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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:simplesearch 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
  
  
  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 per se 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 request body, and MAY process
       request bodies in other formats.
  
  
  Reddy, et al                                        [Page 5]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       If the client sends a text/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.
  
       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.    Etxending 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.
  
  
  2.4.2.    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
  
  
  
  Reddy, et al                                        [Page 6]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <?xml:namespace ns="FOO:" prefix="F"?>
       <D:searchrequest>
          <F:natural-language-query>
            Find the locations of good Thai restaurants in Los Angeles
          </F:natural-language-query>
       </D:searchrequest>
  
  
       >> Response
  
       HTTP/1.1 207 Multi-Status
       Content-Type: text/xml
       Content-Length: 333
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <?xml:namespace ns="http://ryu.com/propschema" prefix="R"?>
       <D:multistatus>
          <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>
  
  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).
  
       - 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 query
          operator.
  
       - 425 Insufficient Space on Resource.   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.
  
  
  
  
  
  
  
  Reddy, et al                                        [Page 7]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  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 425.  It SHOULD
       include the partial results.
  
       SEARCH / HTTP/1.1
       Host: gdr.com
       Content-Type: text/xml
       Connection: Close
       Content-Length: xxxxx
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <D:searchrequest>
          <D:simplesearch>
            … the query goes here …
          </D:simplesearch>
       </D:searchrequest>
  
  
       >> Response
  
       HTTP/1.1 425  Insufficient Space on Resource
       Content-Type: text/xml
       Content-Length: 738
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <D:multistatus>
          <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/1.1 425 Insufficient Space on
       Resource</D:status>
            <D:responsedescription>
               Only first two matching records were returned
            </D:responsedescription>
          </D:response>
       </D:multistatus>
  
  
  Reddy, et al                                        [Page 8]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  3. DISCOVERY OF SUPPORTED QUERY GRAMMARS
  
       Servers MUST support discovery of the query grammars supported by a
       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 ; defined in section 8.4 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 following query grammars:
       http://foo.bar.com/syntax1 and http://akuma.com/syntax2.
  
       >> Request
  
       OPTIONS /somefolder HTTP/1.1
       Connection: Close
       Host: ryu.com
  
  
       >> Response
  
  
  
  Reddy, et al                                        [Page 9]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       HTTP/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: <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:simplesearch 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:simplesearch grammar
       allows a client to discover the set of properties that are
       searchable, selectable, and sortable.  Moreover, although the
       DAV:simplesearch grammar defines a minimal set of operators, it is
       possible that a resource might support additional operators in a
       query.  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.
  
       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
  
  
  
  Reddy, et al                                       [Page 10]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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:simplesearch 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:simplesearch, the scope is also recipes.com.
  
       SEARCH / HTTP/1.1
       Host: recipes.com
       Content-Type: application/xml
       Connection: Close
       Content-Length: 257
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <D:searchrequest>
         <D:simplesearch>
           <D:select>
              <D:queryschema/>
           </D:select>
  
       <D:from><D:scope><D:href>http://recipes.com</d:href></D:scope></D:f
       rom>
         </D:simplesearch>
       </D:searchrequest>
  
       Response:
  
       HTTP/1.1 207 Multistatus
       Content-Type: application/xml
       Content-Length: 428
  
       <?xml version="1.0"?>
       <?xml:namespace ns="DAV:" prefix="D"?>
       <D:multistatus>
         <D:response>
           <D:href>http://recipes.com</D:href>
           <D:propstat>
              <D:prop>
                <D:querygrammar>
                  <D:simplesearchschema>
                      See section 5.19.8 for actual contents
                  </D:simplesearchschema>
  
  
  Reddy, et al                                       [Page 11]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
                </D:querygrammar>
              </D:prop>
              <D:status>HTTP/1.1 200 Okay</D:status>
           </D:propstat>
         </D:response>
       </D:multistatus>
  
  
  5. THE DAV:SIMPLESEARCH GRAMMAR
  
  
  5.1. Introduction
  
       DAV:simplesearch 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:simplesearch has several major components:  DAV:select,
       DAV:from, DAV:where, DAV:sortby, and DAV:limit.  DAV:select
       provides the result record definition.  DAV:from defines the scope.
       DAV:where defines the criteria.  DAV:sortby defines the sort order
       of the result set.  DAV:limit provides constraints on the query as
       a whole.
  
  
  5.2. The DAV:simplesearch DTD
  
       <!ELEMENT simplesearch   (select, from, where?, sortby?, limit?) >
  
       <!ELEMENT select         (allprop | prop) >
  
       <!ELEMENT from           (scope) >
       <!ELEMENT scope          (href, depth?) >
  
  
       <!ELEMENT where          (and | or | not | eq | lt | gt
                              | lte | gte | contentpassthrough ) >
  
       <!ELEMENT and            (and | or | not | eq | lt | gt
                              | lte | gte | isnull | like
                              contentpassthrough) +) >
  
       <!ELEMENT or          ( (and | or | not | eq | lt | gt
                              | lte | gte | isnull | like
                              contentpassthrough) +) >
  
       <!ELEMENT not            (and | or | not | eq | lt | gt
                              | lte | gte | isnull | like
                              contentpassthrough ) >
  
       <!ELEMENT lt          ( prop , literal ) >
       <!ATTLIST lt          casesensitive  (1|0) 1 >
  
       <!ELEMENT lte            ( prop , literal ) >
  
  
  
  Reddy, et al                                       [Page 12]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       <!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)>
  
       <!ELEMENT isnull         (prop) >
       <!ELEMENT like           (prop, literal) >
       <!ELEMENT contentpassthrough       ANY >
  
       <!ELEMENT sortby         (order+) >
       <!ELEMENT order          (prop, (ascending | descending)?)
       <!ATTLIST order          casesensitive
          (1|0) 1 >
       <!ELEMENT ascending      EMPTY>
       <!ELEMENT descending       EMPTY>
  
       <!ELEMENT limit          (nresults) >
       <!ELEMENT nresults       (#PCDATA) >
  
  
  
  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:simplesearch>
          <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:sortby>
  
  
  Reddy, et al                                       [Page 13]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
            <d:order>
                   <d:prop><d:getcontentlength/><d:prop>
                   <d:ascending/>
            </d:order>
          </d:sortby>
       </d:simplesearch>
       </d:searchrequest>
  
  5.3. DAV:select
  
       DAV:select defines the result record. 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.
  
       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 "1", the search
       includes the members of the collection.  When it is "infinity", the
       search includes all recursive members of the collection.8.5.1.
  
  
  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
  
  
  
  Reddy, et al                                       [Page 14]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       an appropriate status code indicating its validity with respect to
       the search arbiter.
  
       Example:
  
       HTTP/1.1 400 Multi-Status
       Content-Type: text/xml
       Content-Length: 428
  
       <?xml version="1.0" ?>
       <?xml:namespace ns="DAV:" prefix="d" ?>
       <d:multistatus>
          <d:response>
            <d:href>http://www.foo.com/scope1</d:href>
            <d:status>HTTP/1.1 502 Bad Gateway</d:status>
          </d:response>
  
          </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).
  
  
  5.5. DAV:where
  
       The 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.
  
  
  
  
  
  
  Reddy, et al                                       [Page 15]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  5.5.3.    Treatment of NULL Values
  
       A NULL value for a property identifies the following conditions:
  
       - The property is not defined on a resource.
  
       - The property is not set on a resource.
  
       - The value of the property is UNKNOWN.
  
       - Security policies prevent the retrieval of the property's value.
  
       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:isnull 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>
  
  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:sortby
  
       The DAV:sortby 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
  
  
  Reddy, et al                                       [Page 16]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       appears before another in the result set.  Comparisons are applied
       in the order they occur in the DAV:sortby 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:sortby 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, c.f.,
       ANSI X3.135-1992).
  
  
  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.
  
  
  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 briefest works appear first.
  
       <d:sortby>
          <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:sortby>
  
  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.
  
  
  
  
  
  
  Reddy, et al                                       [Page 17]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  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.  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.
  
  
  5.11.     DAV:isnull
  
       The DAV:isnull operator allows clients to determine whether a
       property exists on a resource.  The DAV:isnull operator is TRUE if
       and only if a PROPFIND response for the property on that resource
       would return the 403 (Forbidden) or 404 (Not Found) status code.
  
       Example:
  
       <d:isnull>
          <d:prop><x:someprop/></d:prop>
       </d:isnull>
  
  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 )
  
  
  
  
  
  Reddy, et al                                       [Page 18]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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:like>
          <D:prop><D:getcontenttype/></D:prop>
          <D:literal>image%</D:literal>
       </D:like>
  
  5.13.     DAV:contentpassthrough
  
       The DAV:contentpassthrough operator provides an "escape mechanism"
       for accessing content-based comparisons of a resource.  The content
       is server specific, hence not interoperable.  This operator is
       optional.
  
       Rationale:  While it is the intent of the authors to define a set
       of interoperable operators for content based query, (still to be
       designed), we also recognize that advanced content retrieval
       systems will likely have features inappropriate for this protocol,
       and so we wish to provide means whereby as much of a query as
       possible can be standardized while still allowing access to these
       features.  We hope that the ungainly name of this operator will
       convey the sense that it is to be used only as a last resort.  We
       hope that we will be able to define a set of interoperable
       operators sufficient for nearly all the common cases of content
       based search.
  
  
  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
  
  
  
  
  
  Reddy, et al                                       [Page 19]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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:simplesearch
       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:sortby 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.
  
       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.
  
  
  
  
  
  
  Reddy, et al                                       [Page 20]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  5.18.1.   Exampe 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.
        Query Schema for DAV:simplesearch
  
       The DAV:simplesearch 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:
  
       @ the set of properties that may be either searched, returned, or
          used to sort, and a hint about the data type of such properties
  
       @ the set of optional operators defined by the resource.
  
  
  5.19.1. DTD for DAV:simplesearch QSD
  
       <!ELEMENT simplesearchschema  (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.
  
       DASL defines four 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 three
       (DAV:searchable, DAV:selectable, and DAV:sortable) identify
       portions of the query (DAV:where, DAV:select, and DAV:sortby,
  
  
  
  Reddy, et al                                       [Page 21]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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            contents example
  
        Boolean         1
                        0
  
        string          Foobar
  
        int             -259
                        23
  
        float           .314159265358979E+1
                        5.33
  
        dateTime.iso86  1994-11-05T08:15:5Z
        01tz
  
  
  
       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.
  
  
  Reddy, et al                                       [Page 22]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  5.19.6. The DAV:sortable Property Description
  
       This element indicates that the property may appear in the
       DAV:sortby element
  
       <!ELEMENT sortable         EMPTY >
  
  5.19.7. 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:p
       ropdesc>
  
  
  5.19.8. Example of Query Schema for DAV:simplesearch
  
       <?xml:namespace ns="DAV:" prefix="D">
       <?xml:namespace ns="urn:uuid:C2F41010-65B3-11d1-A29F-00AA00C14882/"
       prefix="t"?>
       <?xml:namespace ns="http://jennicam.org" prefix="J">
       <D:simplesearchschema>
         <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:isnull/><D:operand_property/></D:opdesc>
  
       <D:opdesc><D:like/><D:operand_property/><D:operand_literal/></D:opd
       esc>
         </D:operators>
       </D:simplesearchschema>
  
  
  Reddy, et al                                       [Page 23]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  
       This response lists four properties.  The 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:isnull
       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:sortby, or in expressions on properties.)
  
       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.
  
  
  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.
  
  
  
  
  
  
  Reddy, et al                                       [Page 24]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  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
  
       [DASLREQ] S. Reddy, J.Slein, "Requirements for DAV Searching and
       Locating", March  1998, internet-draft, work-in-progress, draft-
       reddy-dasl-requirements-02.txt
  
       [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.
  
       [WebDAV] Y. Goland, E.J. Whitehead, A. Faizi, S.R. Carter, D.
       Jenson, "Extensions for Distributed Authoring on the World Wide
       Web", April. 1998, internet-draft, work-in-progress, draft-ietf-
       webdav-protocol-08.
  
  
  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
  
  
  
  Reddy, et al                                       [Page 25]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       Phone:(650) 506 5441
  
       Rick Henderson
       Netscape
       Email: rickh@netscape.com
  
       Jim Davis
       Xerox PARC
       3333 Coyote Hill Road
       Palo Alto CA 94304
       650-812-4301
       Email: jdavis@parc.xerox.com
  
       Alan Babich
       Filenet
       3565 Harbor Blvd.
       Costa Mesa, CA 92626
       714-966-3403
       Email: ababich@filenet.com
  
  
  15.  APPENDICES
  
  
     Appendix A  Three-Valued Logic in DAV:simplesearch
  
       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.
  
       There are no manifest constants to explicitly represent undefined
       number, string, or datetime values.
  
  
  Reddy, et al                                       [Page 26]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
       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 combinational operators DAV:and, DAV:or and DAV:not are
       evaluated according to the following rules.
  
       For not, not TRUE is FALSE, not FALSE is TRUE, and not UNKNOWN is
       UNKNOWN. (Intuitively speaking, if we don't know if the value
       should be TRUE or FALSE, then if we logically negate the truth
       value, we still don't know whether the truth value should be TRUE
       or FALSE.)
  
       For and, if any of the operands are FALSE, the result is FALSE. If
       no operand is FALSE, then if any operands is UNKNOWN, the result is
       UNKNOWN.  Otherwise, all of the operands are TRUE, and the result
       is TRUE. (Intuitively speaking, if any operand is FALSE, we don't
       care about any of the other operands. If all operands are TRUE, we
       know the result is TRUE.  Otherwise, we don't know whether the
       value should be TRUE or FALSE.)
  
       For or, if any of the operands are TRUE, the result is TRUE. If no
       operand is TRUE, then if any of the operands is UNKNOWN, the result
       is UNKNOWN.  Otherwise, all of the operands are FALSE, and thee
       result is FALSE. (Intuitively speaking, if any operand is TRUE, we
       don't care about the other operands. If all the operands are FALSE,
       we know the value is FALSE.  Otherwise, we don't know whether the
       value should be TRUE or FALSE.)
  
  
  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".
  
  
  
  
  Reddy, et al                                       [Page 27]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  Mar 9, 1998
  
       Moved sub-headings of "Elements of Protocol" to first level and
       removed "Elements of Protocol" Heading.
  
       Added an sentence in introduction explaining that this is a
       "sketch" of a protocol.
  
  
  Mar 11, 1998
  
       Added sortby, data typing, three valued logic, query schema
       property, and element definitions for schema for simplesearch.
  
  
  April 8, 1998
  
       - made changes based on last week’s DASL BOF.
  
  
  May 8, 1998
  
       Removed most of DAV:searcherror; converted to DAV:searchredirect
  
       Altered DAV:simplesearch 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 Author’s 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 now contentspassthrough.  Provide
       examples.  Rename rank to score.
  
  
  
  
  
  Reddy, et al                                       [Page 28]


  INTERNET-DRAFT              DASL      Tuesday, July 28, 1998
  
  
  
  July 28, 1998
  
       Added Dale Lowry as Author
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  Reddy, et al                                       [Page 29]