Network Working GroupJ. Reschke, Editor
Internet-Draftgreenbytes
Intended status: ExperimentalS. Reddy
Expires: October 5, 2007Optena
J. Davis
A. Babich
Filenet
April 3, 2007

Web Distributed Authoring and Versioning (WebDAV) SEARCH
draft-reschke-webdav-search-12

Note: a later version of this document has been published as RFC5323.

Status of this Memo

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This Internet-Draft will expire on October 5, 2007.

Copyright Notice

Copyright © The IETF Trust (2007). All Rights Reserved.

Abstract

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

Editorial Note (To be removed by RFC Editor before publication)

Please send comments to the Distributed Authoring and Versioning (WebDAV) DASL mailing list at <mailto:www-webdav-dasl@w3.org>, which may be joined by sending a message with subject "subscribe" to <mailto:www-webdav-dasl-request@w3.org>. Discussions of the WebDAV DASL mailing list are archived at <http://lists.w3.org/Archives/Public/www-webdav-dasl/>.

An issues list and XML and HTML versions of this draft are available from <http://greenbytes.de/tech/webdav/#draft-reschke-webdav-search>.


Table of Contents

Issues list

IdTypeStatusDateRaised By
update-webdaveditclosed2007-03-10julian.reschke@greenbytes.de
editeditopen2004-07-05julian.reschke@greenbytes.de
 I  edit   (type: edit, status: open)
julian.reschke@greenbytes.de2004-07-05 Umbrella issue for editorial fixes/enhancements.
Associated changes in this document: 1.1, 1.1, 1.1, 1.1, 1.4, 1.5, 2.3, 5.10, 5.10, 5.18, 5.19.3, 5.19.3, 5.19.9, 12.2, 12.2, B.1, B.1, B.5, C.
 I  update-webdav   (type: edit, status: closed)
julian.reschke@greenbytes.de2007-03-10 Update reference from RFC2518 to draft-ietf-webdav-rfc2518bis.
Associated changes in this document: 1.2, 1.3, 1.4, 1.6, 2.1, 2.2.1, 2.2.2, 2.3, 3.2, 4.1, 5.3, 5.10, 5.10, 6, 9, 12.1.

1. Introduction

1.1. DASL

This document defines Web Distributed Authoring and Versioning (WebDAV) SEARCH, an application of HTTP/1.1 forming a lightweight search protocol to transport queries and result sets that allows clients to make use of server-side search facilities. It is based on the expired  I internet draft for DAV Searching & Locating [DASL]. [DASLREQ] describes the motivation for DASL.  I In this specification, the terms "WebDAV SEARCH" and "DASL" are used interchangeably.

DASL  I will minimizeminimizes 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:query-schema-discovery XML element,
  • the DAV:basicsearch XML element and query grammar, and
  • the DAV:basicsearchschema XML element.

For WebDAV-compliant servers, it also defines a new live property DAV:supported-query-grammar-set.

DASL consists of:

  • the SEARCH method and the request/response formats defined for it (Section 2),
  • feature discovery through the "DASL" response header and the optional DAV:supported-grammar-set property (Section 3),
  • optional grammar schema discovery (Section 4) and
  • one mandatory grammar: DAV:basicsearch (Section 5).

1.2. Relationship to DAV

DASL relies on the resource and property model defined by  I [RFC2518][draft-ietf-webdav-rfc2518bis]. DASL does not alter this model. Instead, DASL allows clients to access DAV-modeled resources through server-side search.

1.3. Terms

This document uses the terms defined in [RFC2616], in  I [RFC2518][draft-ietf-webdav-rfc2518bis], in [RFC3253] and in this section.

Criteria

  • An expression against which each resource in the search scope is evaluated.

Query

  • A query is a combination of a search scope, search criteria, result record definition, sort specification, and a search modifier.

Query Grammar

  • A set of definitions of XML elements, attributes, and constraints on their relations and values that defines a set of queries and the intended semantics.

Query Schema

  • A listing, for any given grammar and scope, of the properties and operators that may be used in a query with that grammar and scope.

Result

  • A result is a result set, optionally augmented with other information describing the search as a whole.

Result Record

  • A description of a resource. A result record is a set of properties, and possibly other descriptive information.

Result Record Definition

  • A specification of the set of properties to be returned in the result record.

Result Set

  • A set of records, one for each resource for which the search criteria evaluated to True.

Scope

  • A set of resources to be searched.

Search Modifier

  • An instruction that governs the execution of the query but is not part of the search scope, result record definition, the search criteria, or the sort specification. An example of a search modifier is one that controls how much time the server can spend on the query before giving a response.

Sort Specification

  • A specification of an ordering on the result records in the result set.

1.4. Notational Conventions

This specification uses the Augmented Backus-Naur Form (ABNF) notation of [RFC4234], unless explicitly stated otherwise.

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].

This document uses XML DTD fragments as a purely notational convention. WebDAV request and response bodies can not be validated due to the specific extensibility rules defined in  I Section 23 of [RFC2518]Section 17 of [draft-ietf-webdav-rfc2518bis] and due to the fact that all XML elements defined by this specification use the XML namespace name "DAV:". In particular:

  1. element names use the "DAV:" namespace,
  2. element ordering is irrelevant unless explicitly stated,
  3. extension elements (elements not already defined as valid child elements) may be added anywhere, except when explicitly stated otherwise,
  4. extension attributes (attributes not already defined as valid for this element) may be added anywhere, except when explicitly stated otherwise.

When an XML element type in the "DAV:" namespace is referenced in this document outside of the context of an XML fragment, the string "DAV:" will be prefixed to the element type.

Similar I ily, when an XML element type in the namespace "http://www.w3.org/2001/XMLSchema" is referenced in this document outside of the context of an XML fragment, the string "xs:" will be prefixed to the element type.

1.5. Note on Usage of 'DAV:' XML Namespace

This spe I cification defines elements, properties and condition names in the XML namespace "DAV:". In general, only specifications authored by IETF working groups are supposed to do this. In this case an exception was made, because WebDAV SEARCH started its life in the IETF DASL working group (<http://www.webdav.org/dasl/>, and at the time the working group closed down there was already significant deployment of this specification.

1.6. 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 or application/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 an entity that matches the WebDAV multistatus format ( I [RFC2518], Section 11[draft-ietf-webdav-rfc2518bis], Section 13).

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.

Servers supporting the WebDAV extensions [RFC3253] and/or [RFC3744] MUST also

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 as defined in Section 9.2 of [RFC2616].

If a resource supports the SEARCH method, then the server MUST list SEARCH in the Allow header defined in Section 14.7 of [RFC2616].

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" ":" 1#Coded-URL
Coded-URL  = <defined in  I Section 9.4 of [RFC2518]Section 10.1 of [draft-ietf-webdav-rfc2518bis]>

(This grammar uses the augmented BNF format defined in Section 2.1 of [RFC2616])

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. Note that although the URI can be used to identify each supported search grammar, there is not necessarily a direct relationship between the URI and the XML element name that can be used in XML based SEARCH requests (the element name itself is identified by its namespace name (a URI reference) and the element's local name).

This header MAY be repeated.

For example:

DASL: <http://foobar.example/syntax1> 
DASL: <http://akuma.example/syntax2>
DASL: <DAV:basicsearch>
DASL: <http://example.com/foo/natural-language-query>

3.3. DAV:supported-query-grammar-set (protected)

This WebDAV property is required for any server supporting either [RFC3253] and/or [RFC3744] and identifies the XML based query grammars that are supported by the search arbiter resource.

<!ELEMENT supported-query-grammar-set (supported-query-grammar*)>
<!ELEMENT supported-query-grammar grammar>
<!ELEMENT grammar ANY>

ANY value: a query grammar element type

3.4. Example: Grammar Discovery

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

>> Request:

OPTIONS /somefolder HTTP/1.1
Host: example.org

>> Response:

HTTP/1.1 200 OK
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, SEARCH
DASL: <DAV:basicsearch>
DASL: <http://foobar.example/syntax1> 
DASL: <http://akuma.example/syntax2>

This example shows the equivalent taking advantage of a server's support for DAV:supported-method-set and DAV:supported-query-grammar-set.

>> Request:

PROPFIND /somefolder HTTP/1.1
Host: example.org
Depth: 0
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" encoding="UTF-8" ?>
<propfind xmlns="DAV:">
  <prop>
    <supported-query-grammar-set/>
    <supported-method-set/>
  </prop>
</propfind>

>> Response:

HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
 <response>
  <href>http://example.org/somefolder</href>
  <propstat>
   <prop>
    <supported-query-grammar-set>
     <supported-query-grammar>
      <grammar><basicsearch/></grammar>
     </supported-query-grammar>
     <supported-query-grammar>
      <grammar><syntax1 xmlns="http://foobar.example/"/></grammar>
     </supported-query-grammar>
     <supported-query-grammar>
      <grammar><syntax2 xmlns="http://akuma.example/"/></grammar>
     </supported-query-grammar>
    </supported-query-grammar-set>
    <supported-method-set>
     <supported-method name="COPY" />
     <supported-method name="DELETE" />
     <supported-method name="GET" />
     <supported-method name="HEAD" />
     <supported-method name="LOCK" />
     <supported-method name="MKCOL" />
     <supported-method name="MOVE" />
     <supported-method name="OPTIONS" />
     <supported-method name="POST" />
     <supported-method name="PROPFIND" />
     <supported-method name="PROPPATCH" />
     <supported-method name="PUT" />
     <supported-method name="SEARCH" />
     <supported-method name="TRACE" />
     <supported-method name="UNLOCK" />
    </supported-method-set>
   </prop>
   <status>HTTP/1.1 200 OK</status>
  </propstat>
 </response>
</multistatus>

Note that the query grammar element names marshalled as part of the DAV:supported-query-grammar-set can be directly used as element names in an XML based query.

4. Query Schema Discovery: QSD

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

The DASL response header and the DAV:supported-query-grammar-set property provide 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.

4.1. Additional SEARCH Semantics

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 and with a root element of DAV:query-schema-discovery rather than DAV:searchrequest.

Marshalling:

  • The request body MUST be DAV:query-schema-discovery element.
    <!ELEMENT query-schema-discovery ANY>
    <!-- ANY value: XML element defining a valid query -->
    
  • The response body takes the form of a  I RFC2518 DAV:multistatus elementDAV:multistatus element ([draft-ietf-webdav-rfc2518bis], Section 13), where DAV:response is extended to hold the returned query grammar inside a DAV:query-schema container element.
    <!ELEMENT response (href, ((href*, status)|(propstat+)),
      query-schema?, responsedescription?) >
    <!ELEMENT query-schema ANY>
    

The content of this container 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.

4.1.1. Example of Query Schema Discovery

In this example, the arbiter is recipes.example, the grammar is DAV:basicsearch, the scope is also recipes.example.

>> Request:

SEARCH / HTTP/1.1
Host: recipes.example
Content-Type: application/xml
Content-Length: xxx

<?xml version="1.0"?>
<query-schema-discovery xmlns="DAV:">
  <basicsearch>
    <from>
      <scope>
        <href>http://recipes.example</href>
        <depth>infinity</depth>
      </scope>
    </from>
  </basicsearch>
</query-schema-discovery>

>> Response:

HTTP/1.1 207 Multistatus
Content-Type: application/xml
Content-Length: xxx

<?xml version="1.0"?>
<multistatus xmlns="DAV:">
  <response>  
    <href>http://recipes.example</href>
    <status>HTTP/1.1 200 OK</status>
    <query-schema>
      <basicsearchschema>
        <!-- (See Section 5.19 for
        the actual contents) -->
      </basicsearchschema>
    </query-schema>
  </response>
</multistatus>

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

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 other 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.

5.2. The DAV:basicsearch DTD

<!-- "basicsearch" element -->

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

<!-- "select" element -->

<!ELEMENT select        (allprop | prop) >

<!-- "from" element -->

<!ELEMENT from          (scope+) >
<!ELEMENT scope         (href, depth, include-versions?) >
<!ELEMENT include-versions EMPTY >

<!-- "where" element -->

<!ENTITY %comp_ops      "eq | lt | gt| lte | gte">
<!ENTITY %log_ops       "and | or | not">
<!ENTITY %special_ops   "is-collection | is-defined | 
                         language-defined | language-matches">
<!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|typed-literal)) >
<!ATTLIST lt            caseless   (yes|no) >

<!ELEMENT lte           (prop, (literal|typed-literal)) >
<!ATTLIST lte           caseless   (yes|no) >

<!ELEMENT gt            (prop, (literal|typed-literal)) >
<!ATTLIST gt            caseless   (yes|no) >

<!ELEMENT gte           (prop, (literal|typed-literal)) >
<!ATTLIST gte           caseless   (yes|no) >

<!ELEMENT eq            (prop, (literal|typed-literal)) >
<!ATTLIST eq            caseless   (yes|no) >

<!ELEMENT literal       (#PCDATA)>
<!ELEMENT typed-literal (#PCDATA)>
<!ATTLIST typed-literal xsi:type CDATA implied>

<!ELEMENT is-collection EMPTY >
<!ELEMENT is-defined    (prop) >

<!ELEMENT language-defined    (prop) >
<!ELEMENT language-matches    (prop, literal) >

<!ELEMENT like          (prop, literal) >
<!ATTLIST like          caseless   (yes|no) >

<!ELEMENT contains      (#PCDATA)>

<!-- "orderby" element -->

<!ELEMENT orderby       (order+) >
<!ELEMENT order         ((prop | score), (ascending | descending)?)
<!ATTLIST order         caseless   (yes|no) >
<!ELEMENT ascending     EMPTY>
<!ELEMENT descending    EMPTY>

<!-- "limit" element -->

<!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 xmlns:d="DAV:">
  <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  I [RFC2518] and revised in [RFC3253]Section 14 of [draft-ietf-webdav-rfc2518bis].

5.4. DAV:from

<!ELEMENT scope            (href, depth, include-versions?) >
<!ELEMENT include-versions EMPTY >

DAV:from defines the query scope. This contains one or more DAV:scope elements. Support for multiple scope elements is optional, however servers MUST fail a request specifying multiple DAV:scope elements if they can't support it (see Section 2.2.2, precondition DAV:search-multiple-scope-supported). The scope element contains mandatory DAV:href and DAV:depth elements.

DAV:href indicates the URI 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 collection and its immediate children. When it is "infinity", it includes the collection and all its progeny.

When the scope is not a collection, the depth is ignored and the search applies just to the resource itself.

If the search includes a redirect reference resource (see [RFC4437]), it applies only to that resource, not to its target.

When the child element DAV:include-versions is present, the search scope will include all versions (see [RFC3253], Section 2.2.1) of all version-controlled resources in scope. Servers that do support versioning but do not support the DAV:include-versions feature MUST signal an error if it is used in a query.

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 is an absolute URI reference, 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.

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 contains 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 PROPFIND for a property value would yield a non-2xx (see [RFC2616], Section 10.2) 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 than" a string with length greater than zero.

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

5.5.4. Treatment of Properties with mixed/element Content

Comparisons of properties that do not have simple types (text-only content) is out-of-scope for the standard operators defined for DAV:basicsearch and therefore is defined to be UNKNOWN (as per Appendix A). For querying the DAV:resourcetype property, see Section 5.13.

5.5.5. 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>

5.5.6. 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 (this is compatible with [SQL99]).

The "caseless" attribute may be used to indicate case-sensitivity for comparisons.

5.6.1. Example of Sorting

This sort orders first by last name of the author, and then by size, in descending order, so that for each author, 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 "caseless" 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 "caseless" attribute may be used with these elements.

5.10. DAV:literal

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

White space in literal values is significant in comparisons. For consistency with  I [RFC2518][draft-ietf-webdav-rfc2518bis], clients SHOULD NOT specify the attribute "xml:space" (Section 2.10 of [XML]) to override this behavio I ur.

In comparisons, the contents of DAV:literal SHOULD be treated as string, with the following exceptions:

  • when operand for a comparison with a DAV:getcontentlength property, it SHOULD be treated as an integer value (the behavio I ur for non-integer values is undefined),
  • when operand for a comparison with a DAV:creationdate or DAV:getlastmodified property, it SHOULD be treated as a date value in the ISO-8601 subset defined for the DAV:creationdate property ( I [RFC2518], Section 13.1[draft-ietf-webdav-rfc2518bis], Section 15.1).
  • when operand for a comparison with a property for which the type is known, it MAY be treated according to this type.

5.11. DAV:typed-literal (optional)

There are situations in which a client may want to force a comparison not to be string-based (as defined for DAV:literal). In these cases, a typed comparison can be enforced by using DAV:typed-literal instead.

<!ELEMENT typed-literal (#PCDATA)>

The data type is specified using the xsi:type attribute defined in [XS1], Section 2.6.1. If the type is not specified, it defaults to "xs:string".

A server MUST reject a request with an unknown type.

The comparison evaluates to UNDEFINED if the property value can not be cast to the specified datatype (see [XPATHFUNC], Section 17).

5.11.1. Example for Typed Numerical Comparison

Consider a set of resources with the dead property "edits" in the namespace "http://ns.example.org":

URIproperty value
/a"-1"
/b"01"
/c"3"
/d"test"
/e(undefined)

The expression

<lt xmlns="DAV:"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <prop><edits xmlns="http://ns.example.org"/></prop>
  <typed-literal xsi:type="xs:integer">3</typed-literal>
</lt>

will evaluate to TRUE for the resources "/a" and "/b" (their property values can be parsed as type xs:number, and the numerical comparison evaluates to true), to FALSE for "/c" (property value is compatible, but numerical comparison evaluates to false) and UNKNOWN for "/d" and "/e" (the property either is undefined, or its value can not be parsed as xs:number).

5.12. Support for Matching xml:lang Attributes on Properties

The following two optional operators can be used to express conditions on the language of a property value (as expressed using the xml:lang attribute).

5.12.1. DAV:language-defined (optional)

<!ELEMENT language-defined (prop)>

This operator evaluates to TRUE if the language for the value of the given property is known, FALSE if it isn't and UNKNOWN if the property itself is not defined.

5.12.2. DAV:language-matches (optional)

<!ELEMENT language-matches (prop, literal)>

This operator evaluates to TRUE if the language for the value of the given property is known and matches the language name given in the <literal> element, FALSE if it doesn't match and UNKNOWN if the property itself is not defined.

Languages are considered to match if they are the same, or if the language of the property value is a sublanguage of the language specified in the <literal> element (see [XPATH], Section 4.3, "lang function").

5.12.3. Example of Language-Aware Matching

The expression below will evaluate to TRUE if the property "foobar" exists and its language is either unknown, English or a sublanguage of English.

<or xmlns="DAV:">
  <not>
    <language-defined>
      <prop><foobar/></prop>
    </language-defined>
  </not>
  <language-matches>
    <prop><foobar/></prop>
    <literal>en</literal>
  </language-matches>
</or>

5.13. DAV:is-collection

The DAV:is-collection operator allows clients to determine whether a resource is a collection (that is, whether its DAV:resourcetype element contains the element DAV:collection).

Rationale: This operator 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.

5.13.1. Example of DAV:is-collection

This example shows a search criterion that picks out all and only the resources in the scope that are collections.

<where xmlns="DAV:">
  <is-collection/>
</where>

5.14. DAV:is-defined

The DAV:is-defined 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:is-defined>
  <d:prop><x:someprop/></d:prop>
</d:is-defined>

5.15. 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.

5.15.1. Syntax for the Literal Pattern

pattern       = [wildcard] 0*( text [wildcard] )

wildcard      = exactlyone / zeroormore
text          = 1*( character / escapeseq )

exactlyone    = "_"
zeroormore    = "%"
escapechar    = "\"
escapeseq     = "\" ( exactlyone / zeroormore / escapechar ) 

; character: see [XML], Section 2.2, minus wildcard / escapechar
character     = HTAB / LF / CR ; whitespace
character     =/ %x20-24 / %x26-5B / %x5D-5E / %x60-D7FF
character     =/ %xE000-FFFD / %x10000-10FFFF

The value for the literal is composed of wildcards separated by segments of text. Wildcards may begin or end the literal.

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.

5.15.2. 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 caseless="yes">
    <D:prop><D:getcontenttype/></D:prop>
    <D:literal>image/%</D:literal>
  </D:like>
</D:where>

5.16. 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.

5.16.1. Result Scoring (DAV:score Element)

Servers SHOULD indicate scores for the DAV:contains condition by adding a DAV:score XML element to the DAV:response element. Its value is defined only in the context of a particular query result. 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).

Modified DTD fragment for DAV:propstat:

<!ELEMENT response (href, ((href*, status)|(propstat+)),
                    responsedescription?, score?) >
<!ELEMENT score    (#PCDATA) >

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

5.16.2. Ordering by Score

To order search results by their score, the DAV:score element may be added as child to the DAV:orderby element (in place of a DAV:prop element).

5.16.3. 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>

5.17. Limiting the Result Set

<!ELEMENT limit (nresults) >
<!ELEMENT nresults (#PCDATA)> ;only digits

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. The DAV:nresults XML element contains a requested maximum number of DAV:response elements to be returned in the response body. The server MAY disregard this limit. The value of this element is an integer.

5.17.1. Relationship to Result Ordering

If the result set is both limited by DAV:limit and ordered according to DAV:orderby, the results that are included in the response document must be those that order highest.

5.18. The 'caseless' XML Attribute

The "caseless" attribute allows clients to specify caseless matching behavio I ur instead of character-by-character matching for DAV:basicsearch operators.

The possible values for "caseless" are "yes" or "no". The default value is server-specified. Caseless matching SHOULD be implemented as defined in section 5.18 of the Unicode Standard ([UNICODE4]).

Support for the "caseless" attribute is optional. A server should respond with a status of 422 if it is used but cannot be supported.

5.19. Query Schema 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 properties that may be either searched, returned, or used to sort, and a hint about the data type of such properties
  2. the set of optional operators defined by the resource.

5.19.1. DTD for DAV:basicsearch QSD

<!ELEMENT basicsearchschema  (properties, operators)>
<!ELEMENT any-other-property EMPTY>
<!ELEMENT properties         (propdesc*)>
<!ELEMENT propdesc           (prop|any-other-property), datatype?,
                              searchable?, selectable?, sortable?,
                              caseless?)>
<!ELEMENT operators          (opdesc*)>
<!ELEMENT opdesc             ANY>
<!ELEMENT operand-literal    EMPTY>
<!ELEMENT operand-typed-literal EMPTY>
<!ELEMENT operand-property   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 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:caseless) 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.

5.19.2.1. DAV:any-other-property

This element can be used in place of DAV:prop to describe properties of WebDAV properties not mentioned in any other DAV:prop element. For instance, this can be used to indicate that all other properties are searchable and selectable without giving details about their types (a typical scenario for dead properties).

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. Data I  types are identified by an element name. Where appropriate, a server SHOULD use the simple data I  types defined in [XS2].

<!ELEMENT datatype ANY >

Examples from [XS2], Section 3:

Qualified nameExample
xs:booleantrue, false, 1, 0
xs:stringFoobar
xs:dateTime1994-11-05T08:15:5Z
xs:float.314159265358979E+1
xs:integer-259, 23

If the data type of a property is not given, then the data type defaults to xs: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>

5.19.7. The DAV:caseless Property Description

This element only applies to properties whose data type is "xs:string" and derived data types 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 caseless (the default is character-by-character).

<!ELEMENT caseless 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, DAV:operand-literal or DAV:operand-typed-literal, which indicate that the operand in the corresponding position is a property, a literal value or a typed literal value, respectively. If an operator is polymorphic (allows more than one operand syntax) then each permitted syntax MUST be listed separately.

<operators xmlns='DAV:'>
  <opdesc>
    <like/><operand-property/><operand-literal/>
  </opdesc>
</operators>

5.19.9. Example of Query Schema for DAV:basicsearch

<D:basicsearchschema xmlns:D="DAV:"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"">
  <D:properties>
    <D:propdesc>
      <D:prop><D:getcontentlength/></D:prop>
      <D:datatype><xs:nonNegativeInteger/></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><fstop xmlns="http://jennicam.org"/></D:prop>
      <D:selectable/>
    </D:propdesc>
    <D:propdesc>
      <D:any-other-property/>
      <D:searchable/><D:selectable/>
    </D:propdesc>
  </D:properties>
  <D:operators>
    <D:opdesc>
      <D:like/><D:operand-property/><D:operand-literal/>
    </D:opdesc>
  </D:operators>
</D:basicsearchschema>

This response lists four properties. The data I  type of the last three properties is not given, so it defaults to xs: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:is-defined and DAV:like are supported.

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

6. Internationalization Considerations

Properties may be language-tagged using the xml:lang attribute (see  I [RFC2518], Section 4.4[draft-ietf-webdav-rfc2518bis], Section 4.3). The optional operators DAV:language-defined (Section 5.12.1) and DAV:language-matches (Section 5.12.2) allow to express conditions on the language tagging information.

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 [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 [XML]. However, [XML] does state that an XML processor may, at its discretion, include the external XML entity.

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 [RFC3023]. 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. IANA Considerations

This document uses the namespace defined in  I Section 18 of [RFC2518]Section 21 of [draft-ietf-webdav-rfc2518bis] for XML elements.

9.1. HTTP Headers

This document specifies the HTTP header listed below, to be added to the HTTP header registry defined in [RFC3864].

9.1.1. DASL

Header field name:
DASL
Applicable protocol:
http
Status:
Experimental
Author/Change controller:
IETF
Specification document:
this specification (Section 3.2)

10. Contributors

This document is based on prior work on the DASL protocol done by the WebDAV DASL working group until the year 2000 -- namely by Alan Babich, Jim Davis, Rick Henderson, Dale Lowry, Saveen Reddy and Surendra Reddy.

11. Acknowledgements

This document has benefited from thoughtful discussion by Lisa Dusseault, Sung Kim, Elias Sinderson, Martin Wallmer, Keith Wannamaker, Jim Whitehead and Kevin Wiggen.

12. References

12.1. Normative References

[RFC2518]Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D. Jensen, “HTTP Extensions for Distributed Authoring -- WEBDAV”, RFC 2518, February 1999.
[draft-ietf-webdav-rfc2518bis]Dusseault, L., Ed., “HTTP Extensions for Distributed Authoring - WebDAV RFC2518 bis”, Internet-Draft draft-ietf-webdav-rfc2518bis-18 (work in progress), February 2007.
[RFC2119]Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.
[RFC2616]Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1”, RFC 2616, June 1999.
[RFC3023]Makoto, M., St.Laurent, S., and D. Kohn, “XML Media Types”, RFC 3023, January 2001.
[RFC3253]Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV”, RFC 3253, March 2002.
[RFC3744]Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, “Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol”, RFC 3744, May 2004.
[RFC4234]Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF”, RFC 4234, October 2005.
[RFC4437]Whitehead, J., Clemm, G., and J. Reschke, Ed., “Web Distributed Authoring and Versioning (WebDAV) Redirect Reference Resources”, RFC 4437, March 2006.
[XML]Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F. Yergeau, “Extensible Markup Language (XML) 1.0 (Fourth Edition)”, W3C REC-xml-20060816, August 2006, <http://www.w3.org/TR/2006/REC-xml-20060816>.
[XPATH]Clark, J. and S. DeRose, “XML Path Language (XPath) Version 1.0”, W3C REC-xpath-19991116, November 1999, <http://www.w3.org/TR/1999/REC-xpath-19991116>.
[XPATHFUNC]Malhotra, A., Melton, J., and N. Walsh, “XQuery 1.0 and XPath 2.0 Functions and Operators”, W3C REC-xpath-functions-20070123, January 2007, <http://www.w3.org/TR/2007/REC-xpath-functions-20070123/>.
[XS1]Thompson, H., Beech, D., Maloney, M., Mendelsohn, N., and World Wide Web Consortium, “XML Schema Part 1: Structures”, W3C REC-xmlschema-1-20041028, October 2004, <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/>.
[XS2]Biron, P., Malhotra, A., and World Wide Web Consortium, “XML Schema Part 2: Datatypes Second Edition”, W3C REC-xmlschema-2-20041028, October 2004, <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/>.

12.2. Informative References

[DASL]Reddy, S., Lowry, D., Reddy, S., Henderson, R., Davis, J., and A. Babich, “DAV Searching & Locating”, Internet-Draft draft-ietf-dasl-protocol-00 (work in progress), July 1999.
[DASLREQ]Davis, J., Reddy, S., and J. Slein, “Requirements for DAV Searching and Locating”, February 1999, <http://www.webdav.org/dasl/requirements/draft-dasl-requirements-01.html>.
This is an updated version of the Internet Draft "draft-ietf-dasl-requirements-00", but obviously never was submitted to the IETF.
[BIND]Clemm, G., Crawford, J., Reschke, J., Ed., and J. Whitehead, “Binding Extensions to WebDAV”, Internet-Draft draft-ietf-webdav-bind-17 (work in progress), February 2007.
[draft-ietf-webdav-bind]Clemm, G., Crawford, J., Reschke, J., Ed., and J. Whitehead, “Binding Extensions to Web Distributed Authoring and Versioning (WebDAV)”, Internet-Draft draft-ietf-webdav-bind-18 (work in progress), March 2007.
[RFC3864]Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields”, BCP 90, RFC 3864, September 2004.
[RFC4790]Newman, C., Duerst, M., and A. Gulbrandsen, “Internet Application Protocol Collation Registry”, RFC 4790, March 2007.
[SQL99]Milton, J., “Database Language SQL Part 2: Foundation (SQL/Foundation)”, ISO ISO/IEC 9075-2:1999 (E), July 1999.
[UNICODE4]The Unicode Consortium, “The Unicode Standard - Version 4.0”, Addison-Wesley, August 2003, <http://www.unicode.org/versions/Unicode4.0.0/>.
ISBN 0321185781

A. 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, 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.

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:

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

B. Unresolved Issues

This Section summarizes issues which have been raised during the development of this specification, but for which no resolution could be found with the constraints in place. At the time of this writing, not resolving these issues and publishing as "Experimental" seemed to make more sense than not publishing at all. Future revisions of this specification should revisit these issues, though.

B.1. Collation Support

Matching and sorting of textual data relies on collations. With respect to WebDAV SEARCH, a combination of various design approaches could be used:

  • Require server support for specific collations.
  • Require that the server can advertise which collations it supports.
  • Allow a client to select the collation to be used.

In practice, the current implementations of WebDAV SEARCH usually rely on backends they do not control, and for which collation information may not be available. To make things worse, implementations of the DAV:basicsearch grammar frequently need to combine data from multiple underlying stores (such as properties and full text content), and thus collation support may vary based on the operator or property.

Another open issue is what collation formalism to support. At the time of this writing, the two specifications below seem to provide the necessary framework and thus may be the base for future work on collation support in WebDAV SEARCH:

  1. "Internet Application Protocol Collation Registry" ( I <http://www.ietf.org/internet-drafts/draft-newman-i18n-comparator-14.txt>[RFC4790]).
  2. "XQuery 1.0 and XPath 2.0 Functions and Operators" ( I <http://www.w3.org/TR/xquery-operators/#collations>[XPATHFUNC], Section 7.3.1).

B.2. Count

DAV:basicsearch does not allow a request that returns the count of matching resources.

A protocol extension would need to extend DAV:select, and also modify the DAV:multistatus response format.

B.3. Matching Media Types

Matching media types using the DAV:getcontenttype property and the DAV:like operator is hard due to DAV:getcontenttype also allowing parameters. A new operator specifically designed for the purpose of matching media types probably would simplify things a lot. See <http://lists.w3.org/Archives/Public/www-webdav-dasl/2003OctDec/0109.html> for a specific proposal.

B.4. Query by Name

DAV:basicsearch operates on the properties (and optionally the contents) of resources, and thus doesn't really allow matching on parts of the resource's URI. See <http://lists.w3.org/Archives/Public/www-webdav-dasl/2003OctDec/0100.html> for a proposed extension covering this use case.

B.5. Result Paging

A frequently discussed feature is the ability to specifically request the "next" set of results, when either the server decided to truncate the result, or the client explicitly asked for a limited set (for insta I nce, using the DAV:limit element defined in Section 5.17).

In this case, it would be desirable if the server could keep the full query result, and provide a new URI identifying a separate result resource, allowing the client to retrieve additional data through GET requests, and remove the result through a DELETE request.

C. Change Log (to be removed by RFC Editor before publication)

C.1. From draft-davis-dasl-protocol-xxx

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.
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 week's 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 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 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 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.
April 20, 2000
Removed redirection feature, since 301/302 suffices. Removed Query Schema Discovery (former chapter 4). Everyone agrees this is a useful feature, but it is apparently too difficult to define at this time, and it is not essential for DASL.

C.2. since start of draft-reschke-webdav-search

October 09, 2001
Added Julian Reschke as author.
Chapter about QSD re-added.
Formatted into RFC2629-compliant XML document.
Added first comments.
ID version number kicked up to draft-dasl-protocol-03.
October 17, 2001
Updated address information for Jim Davis.
Added issue of datatype vocabularies.
Updated issue descriptions for grammar discovery, added issues on query schema DTD.
Fixed typos in XML examples.
December 17, 2001
Re-introduced split between normative and non-normative references.
January 05, 2002
Version bumped up to 04. Started work on resolving the issues identified in the previous version.
January 14, 2002
Fixed some XML typos.
January 22, 2002
Closed issues naming-of-elements. Fixed query search DTD and added option to discover properties of "other" (non-listed) properties.
January 25, 2002
Changed into private submission and added reference to historic DASL draft. Marked reference to DASL requirements non-normative.
Updated reference to latest deltav spec.
January 29, 2002
Added feedback from and updated contact info for Alan Babich.
Included open issues collected in http://www.webdav.org/dasl/protocol/issues.html.
February 8, 2002
Made sure that all artwork fits into 72 characters wide text.
February 18, 2002
Changed Insufficient storage handling (multistatus). Moved is-collection to operators and added to DTD. Made scope/depth mandatory.
February 20, 2002
Updated reference to SQL99.
February 28, 2002
"Non-normative References" -> "Informative References". Abstract updated. Consistently specify a charset when using text/xml (no change bars). Do not attempt to define PROPFIND's entity encoding (take out specific references to text/xml). Remove irrelevant headers (Connection:) from examples (no change bars). Added issue on querying based on DAV:href. Updated introduction to indicate relationship to DASL draft. Updated HTTP reference from RFC2068 to RFC2616. Updated XML reference to XML 1.0 2nd edition.
March 1, 2002
Removed superfluous namespace decl in 2.4.2. Reopened JW14 and suggest to drop xml:space support.
March 3, 2002
Removed "xml:space" feature on DAV:literal. Added issue about string comparison vs. collations vs. xml:lang. Updated some of the open issues with details from JimW's original mail in April 1999. Resolved scope vs relative URI references. Resolved issues about DAV:ascending (added to index) and the BNF for DAV:like (changed "octets" to "characters").
March 8, 2002
Updated reference to DeltaV (now RFC3253). Added Martin Wallmer's comments, moved JW5 into DAV:basicsearch section.
March 11, 2002
Closed open issues regaring the type of search arbiters (JW3) and their discovery (JW9). Rephrased requirements on multistatus response bodies (propstat only if properties were selected, removed requirement for responsedescription).
March 23, 2002
RFC2376 -> RFC3023. Added missing first names of authors. OPTIONS added to example for DAV:supported-method-set.

C.3. since draft-reschke-webdav-search-00

March 29, 2002
Abstract doesn't refer to DASL WG anymore.
April 7, 2002
Fixed section title (wrong property name supported-search-grammar-set. Changed DAV:casesensitve to "casesensitive" (it wasn't in the DAV: namespace after all).
May 28, 2002
Updated some issues with Jim Davis's comments.
June 10, 2002
Added proposal for different method for query schema discovery, not using pseudo-properties.
June 25, 2002
QSD marshalling rewritten. Added issue "isdefined-optional".

C.4. since draft-reschke-webdav-search-01

July 04, 2002
Added issue "scope-collection".
July 08, 2002
Closed issue "scope-collection".
August 12, 2002
Added issues "results-vs-binds" and "select-allprop".
October 22, 2002
Added issue "undefined-expressions".
November 18, 2002
Changed example host names (no change tracking).
November 25, 2002
Updated issue "DB2/DB7". Closed issues "undefined expressions", "isdefined-optional" and "select-allprop".

C.5. since draft-reschke-webdav-search-02

November 27, 2002
Added issues "undefined-properties", "like-exactlyone" and "like-wildcard-adjacent". Closed issue "query-on-href". Added acknowledgments section.
November 28, 2002
Closed issue "like-exactlyone". Added issue "mixed-content-properties".
December 14, 2002
Closed issues "undefined-properties", "results-vs-binds", "mixed-content-properties". Updated issue "like-wildcard-adjacent". Added informative reference to BIND draft. Updated reference to ACL draft.
January 9, 2003
Removed duplicate section on invalid scopes. Added comments to some open issues. Closed issues JW25/26, score-pseudo-property and null-ordering.
January 10, 2003
Issue limit-vs-ordering plus resolution. Closed issue JW17/JW24b.
January 14, 2003
New issue order-precedence. Started resolution of DB2/DB7.
January 15, 2003
Started spec of DAV:typed-literal.
January 17, 2003
Fix one DAV:like/DAV:getcontenttype example (add / to like expression, make case-insensitive).
January 28, 2003
Update issue(s) result-truncation, JW24d. Fixed response headers in OPTIONS example. Added issue qsd-optional. Closed issue(s) order-precedence, case-insensitivity-name.
February 07, 2003
Added issue scope-vs-versions. score-pseudo-property: allow DAV:orderby to explicitly specify DAV:score.

C.6. since draft-reschke-webdav-search-03

April 24, 2003
Fixed two "?" vs "_" issues (not updated in last draft).
June 13, 2003
Improve index.

C.7. since draft-reschke-webdav-search-04

July 7, 2003
Typo fixed (propstat without status element).
August 11, 2003
Remove superfluous IP and copyright sections.
September 09, 2003
Added issues "2.4-multiple-uris" and "5.1-name-filtering".
October 06, 2003
Fix misplaced section end in 5.11, add table formatting. Enhance table formatting in 5.18.3. Updated ACL and BIND references. Added XPATH reference. Closed issue JW24d by adding new optional operators. Updated more open issues, added issues from January meeting. Add K. Wiggen to Acknowledgements. Add Contributors section for the authors of the original draft. Close issue "scope-vs-versions" (optional feature added). Close (new) issue "1.3-import-DTD-terminology". Add issue "1.3-import-requirements-terminology".
October 07, 2003
Typos fixed. Moved statement about DAV: namespace usage into separate (sub-)section. Closed "1.3-import-requirements-terminology". Update I18N Considerations with new xml:lang support info (see issue JW24d). Close issue "DB2/DB7" (remaining typing issues are now summarized in issue "typed-literal"). Fix misplaced section end in section 7. Started change to use RFC3253-style method definitions and error marshalling.
October 08, 2003
Remove obsolete language that allowed reporting invalid scopes and such inside multistatus. Add new issue "5.4.2-scope-vs-redirects".

C.8. since draft-reschke-webdav-search-05

October 11, 2003
Separate DAV:basicsearch DTD into separate figures for better maintainability. Update DTD with language-* operators and typed-literal element (optional).
October 14, 2003
Close issue "5.4.2-multiple-scope".
November 04, 2003
Update reference from CaseMap to UNICODE4, section 5.18.
November 16, 2003
Updated issue "5.1-name-filtering".
November 24, 2003
Reformatted scope description (collection vs. non-collection).
November 30, 2003
Add issue "5_media_type_match".
February 6, 2004
Updated all references.

C.9. since draft-reschke-webdav-search-06

July 05, 2004
Fix table in Appendix "Three-Valued Logic in DAV:basicsearch".
September 14, 2004
Fix inconsistent DTD in section 5.2 and 5.4 for scope element.
September 30, 2004
Rewrite editorial note and abstract. Update references (remove unneeded XMLNS, update ref to ACL and BIND specs).

C.10. since draft-reschke-webdav-search-07

October 01, 2004
Fix previous section heading (no change tracking).
October 13, 2004
Fix DTD entry for is-collection.
November 1, 2004
Fix DTD fragment query-schema-discovery.
December 11, 2004
Update BIND reference.
January 01, 2005
Fix DASL and DASLREQ references.
February 06, 2005
Update XS2 reference.
February 11, 2005
Rewrite "like" and "DASL" (response header) grammar in ABNF.
May 5, 2005
Update references. Close issue "abnf" (only use ABNF when applicable).

C.11. since draft-reschke-webdav-search-08

May 06, 2005
Fix document title.
September 25, 2005
Update BIND reference.
October 05, 2005
Update RFC4234 reference.
October 22, 2005
Author's address update.
February 12, 2006
Update BIND reference.
March 16, 2006
Add typed literals to QSD.
August 20, 2006
Update XML reference.
August 28, 2006
Add issues "5.3-select-count" (open) and "5.4-clarify-depth" (resolved). Update BIND reference (again).

C.12. since draft-reschke-webdav-search-09

December 1, 2006
Fix ABNF for DASL header.
December 16, 2006
Close issue "qsd-optional", leave QSD optional. Close issue "2.4-multiple-uris", suggesting that servers should only return one response element per resource in case of multiple bindings. Add and resolve issues "authentication" and "cleanup-iana" (adding the header registration for "DASL"). Re-write rational for using the DAV: namespace, although this is a non-WG submission.
January 4, 2007
Close issue "JW16b/JW24a", being related to "language-comparison". Add Appendix B. Close issues "language-comparison", "5_media_type_match", "5.1-name-filtering" and "5.3-select-count" as "won't fix", and add appendices accordingly.
January 24, 2007
Update BIND reference. Close issue "5.4.2-scope-vs-redirects". Close issue "typed-literal": specify in terms of the XPATH 2.9 casting mechanism. Close issue "1.3-apply-condition-code-terminology" (no changes).

C.13. since draft-reschke-webdav-search-10

January 29, 2007
Issue "result-truncation": Add appendix describing the open issue of Result Paging. Describe the mechanism of marshalling truncated results in a new normative subsection (leave the actual example where it was). Add and resolve issues "rfc2606-compliance" and "response-format". Update contact information for Alan Babich, Jim Davis and Surendra Reddy (no change tracking).
February 8, 2007
Update BIND reference.
 I  

C.14. since draft-reschke-webdav-search-11

Update: draft-newman-i18n-comparator-14 is RFC4790. Update: RFC2518 replaced by draft-ietf-webdav-rfc2518bis. Updated BIND reference. Minox tweaks to intro (document organization and relation to DASL).

Index

B C D M O P Q R S U X

Authors' Addresses

Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/

Surendra Reddy
Optena Corporation
2860 Zanker Road, Suite 201
San Jose, CA 95134
U.S.A.
Phone: +1 408 321 9006
EMail: skreddy@optena.com

Jim Davis
27 Borden Street
Toronto, Ontario M5S 2M8
Canada
Phone: +1 416 929 5854
EMail: jrd3@alum.mit.edu
URI: http://www.econetwork.net/~jdavis

Alan Babich
Filenet, an IBM company
3565 Harbor Blvd.
Costa Mesa, CA 92626
U.S.A.
Phone: +1 714 327 3403
EMail: ababich@us.ibm.com

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