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rfc:rfc5323

Network Working Group J. Reschke, Ed. Request for Comments: 5323 greenbytes Category: Standards Track S. Reddy

                                                                Mitrix
                                                              J. Davis
                                                             A. Babich
                                                                   IBM
                                                         November 2008
      Web Distributed Authoring and Versioning (WebDAV) SEARCH

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (c) 2008 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents (http://trustee.ietf.org/
 license-info) in effect on the date of publication of this document.
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.

Abstract

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

Reschke, et al. Standards Track [Page 1] RFC 5323 WebDAV SEARCH November 2008

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.  DASL . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.2.  Relationship to DAV  . . . . . . . . . . . . . . . . . . .  4
   1.3.  Terms  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   1.4.  Notational Conventions . . . . . . . . . . . . . . . . . .  6
   1.5.  Note on Usage of 'DAV:' XML Namespace  . . . . . . . . . .  7
   1.6.  An Overview of DASL at Work  . . . . . . . . . . . . . . .  7
 2.  The SEARCH Method  . . . . . . . . . . . . . . . . . . . . . .  7
   2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.2.  The Request  . . . . . . . . . . . . . . . . . . . . . . .  8
     2.2.1.  The Request-URI  . . . . . . . . . . . . . . . . . . .  8
     2.2.2.  The Request Body . . . . . . . . . . . . . . . . . . .  8
   2.3.  The Successful 207 (Multistatus) Response  . . . . . . . .  9
     2.3.1.  Result Set Truncation  . . . . . . . . . . . . . . . .  9
     2.3.2.  Extending the PROPFIND Response  . . . . . . . . . . . 10
     2.3.3.  Example: A Simple Request and Response . . . . . . . . 10
     2.3.4.  Example: Result Set Truncation . . . . . . . . . . . . 11
   2.4.  Unsuccessful Responses . . . . . . . . . . . . . . . . . . 12
     2.4.1.  Example of an Invalid Scope  . . . . . . . . . . . . . 12
 3.  Discovery of Supported Query Grammars  . . . . . . . . . . . . 13
   3.1.  The OPTIONS Method . . . . . . . . . . . . . . . . . . . . 13
   3.2.  The DASL Response Header . . . . . . . . . . . . . . . . . 14
   3.3.  DAV:supported-query-grammar-set (Protected)  . . . . . . . 14
   3.4.  Example: Grammar Discovery . . . . . . . . . . . . . . . . 15
 4.  Query Schema Discovery: QSD  . . . . . . . . . . . . . . . . . 17
   4.1.  Additional SEARCH Semantics  . . . . . . . . . . . . . . . 17
     4.1.1.  Example of Query Schema Discovery  . . . . . . . . . . 18
 5.  The DAV:basicsearch Grammar  . . . . . . . . . . . . . . . . . 19
   5.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 19
   5.2.  The DAV:basicsearch DTD  . . . . . . . . . . . . . . . . . 20
     5.2.1.  Example Query  . . . . . . . . . . . . . . . . . . . . 22
   5.3.  DAV:select . . . . . . . . . . . . . . . . . . . . . . . . 23
   5.4.  DAV:from . . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.4.1.  Relationship to the Request-URI  . . . . . . . . . . . 23
     5.4.2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . 24
   5.5.  DAV:where  . . . . . . . . . . . . . . . . . . . . . . . . 24
     5.5.1.  Use of Three-Valued Logic in Queries . . . . . . . . . 24
     5.5.2.  Handling Optional Operators  . . . . . . . . . . . . . 24
     5.5.3.  Treatment of NULL Values . . . . . . . . . . . . . . . 24
     5.5.4.  Treatment of Properties with Mixed/Element Content . . 25
     5.5.5.  Example: Testing for Equality  . . . . . . . . . . . . 25
     5.5.6.  Example: Relative Comparisons  . . . . . . . . . . . . 25
   5.6.  DAV:orderby  . . . . . . . . . . . . . . . . . . . . . . . 26
     5.6.1.  Example of Sorting . . . . . . . . . . . . . . . . . . 26
   5.7.  Boolean Operators: DAV:and, DAV:or, and DAV:not  . . . . . 26
   5.8.  DAV:eq . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Reschke, et al. Standards Track [Page 2] RFC 5323 WebDAV SEARCH November 2008

   5.9.  DAV:lt, DAV:lte, DAV:gt, DAV:gte . . . . . . . . . . . . . 27
   5.10. DAV:literal  . . . . . . . . . . . . . . . . . . . . . . . 27
   5.11. DAV:typed-literal (Optional) . . . . . . . . . . . . . . . 28
     5.11.1. Example for Typed Numerical Comparison . . . . . . . . 28
   5.12. Support for Matching xml:lang Attributes on Properties . . 29
     5.12.1. DAV:language-defined (Optional)  . . . . . . . . . . . 29
     5.12.2. DAV:language-matches (Optional)  . . . . . . . . . . . 29
     5.12.3. Example of Language-Aware Matching . . . . . . . . . . 29
   5.13. DAV:is-collection  . . . . . . . . . . . . . . . . . . . . 30
     5.13.1. Example of DAV:is-collection . . . . . . . . . . . . . 30
   5.14. DAV:is-defined . . . . . . . . . . . . . . . . . . . . . . 30
   5.15. DAV:like . . . . . . . . . . . . . . . . . . . . . . . . . 30
     5.15.1. Syntax for the Literal Pattern . . . . . . . . . . . . 31
     5.15.2. Example of DAV:like  . . . . . . . . . . . . . . . . . 31
   5.16. DAV:contains . . . . . . . . . . . . . . . . . . . . . . . 31
     5.16.1. Result Scoring (DAV:score Element) . . . . . . . . . . 32
     5.16.2. Ordering by Score  . . . . . . . . . . . . . . . . . . 33
     5.16.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 33
   5.17. Limiting the Result Set  . . . . . . . . . . . . . . . . . 33
     5.17.1. Relationship to Result Ordering  . . . . . . . . . . . 33
   5.18. The 'caseless' XML Attribute . . . . . . . . . . . . . . . 34
   5.19. Query Schema for DAV:basicsearch . . . . . . . . . . . . . 34
     5.19.1. DTD for DAV:basicsearch QSD  . . . . . . . . . . . . . 34
     5.19.2. DAV:propdesc Element . . . . . . . . . . . . . . . . . 35
     5.19.3. The DAV:datatype Property Description  . . . . . . . . 35
     5.19.4. The DAV:searchable Property Description  . . . . . . . 36
     5.19.5. The DAV:selectable Property Description  . . . . . . . 36
     5.19.6. The DAV:sortable Property Description  . . . . . . . . 36
     5.19.7. The DAV:caseless Property Description  . . . . . . . . 36
     5.19.8. The DAV:operators XML Element  . . . . . . . . . . . . 37
     5.19.9. Example of Query Schema for DAV:basicsearch  . . . . . 38
 6.  Internationalization Considerations  . . . . . . . . . . . . . 39
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 39
   7.1.  Implications of XML External Entities  . . . . . . . . . . 39
 8.  Scalability  . . . . . . . . . . . . . . . . . . . . . . . . . 40
 9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 40
   9.1.  HTTP Headers . . . . . . . . . . . . . . . . . . . . . . . 40
     9.1.1.  DASL . . . . . . . . . . . . . . . . . . . . . . . . . 40
 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 41
 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 41
 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
   12.1. Normative References . . . . . . . . . . . . . . . . . . . 41
   12.2. Informative References . . . . . . . . . . . . . . . . . . 42
 Appendix A.  Three-Valued Logic in DAV:basicsearch . . . . . . . . 44
 Appendix B.  Candidates for Future Protocol Extensions . . . . . . 45
   B.1.  Collation Support  . . . . . . . . . . . . . . . . . . . . 45
   B.2.  Count  . . . . . . . . . . . . . . . . . . . . . . . . . . 46
   B.3.  Diagnostics for Unsupported Queries  . . . . . . . . . . . 46

Reschke, et al. Standards Track [Page 3] RFC 5323 WebDAV SEARCH November 2008

   B.4.  Language Matching  . . . . . . . . . . . . . . . . . . . . 46
   B.5.  Matching Media Types . . . . . . . . . . . . . . . . . . . 46
   B.6.  Query by Name  . . . . . . . . . . . . . . . . . . . . . . 46
   B.7.  Result Paging  . . . . . . . . . . . . . . . . . . . . . . 46
   B.8.  Search Scope Discovery . . . . . . . . . . . . . . . . . . 47
 Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

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
 earlier work done in the IETF DASL Working Group (see Section 10).
 In this specification, the terms "WebDAV SEARCH" and "DASL" are used
 interchangeably.
 DASL minimizes the complexity of clients so as to facilitate
 widespread deployment of applications capable of utilizing the DASL
 search mechanisms.
 DASL consists of:
 o  the SEARCH method and the request/response formats defined for it
    (Section 2),
 o  feature discovery through the "DASL" response header and the
    optional DAV:supported-grammar-set property (Section 3),
 o  optional grammar schema discovery (Section 4), and
 o  one mandatory grammar: DAV:basicsearch (Section 5).

1.2. Relationship to DAV

 DASL relies on the resource and property model defined by [RFC4918].
 DASL does not alter this model.  Instead, DASL allows clients to
 access DAV-modeled resources through server-side search.

Reschke, et al. Standards Track [Page 4] RFC 5323 WebDAV SEARCH November 2008

1.3. Terms

 This document uses the terms defined in [RFC2616], [RFC4918],
 [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.

Reschke, et al. Standards Track [Page 5] RFC 5323 WebDAV SEARCH November 2008

 Scope
    A set of resources to be searched.
 Search Arbiter
    A resource that supports the SEARCH method.
 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 [RFC5234], 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 ([XML], Section 3.2) as a purely
 notational convention.  WebDAV request and response bodies cannot be
 validated by a DTD due to the specific extensibility rules defined in
 Section 17 of [RFC4918] 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.

Reschke, et al. Standards Track [Page 6] RFC 5323 WebDAV SEARCH November 2008

 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.
 Similarly, 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.
 This document inherits, and sometimes extends, DTD productions from
 Section 14 of [RFC4918].

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

 This specification 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:
 o  The client constructs a query using the DAV:basicsearch grammar.
 o  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.
 o  The search arbiter performs the query.
 o  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 ([RFC4918], Section 13).

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 an entity matching the WebDAV multistatus format ([RFC4918],
 Section 13).

Reschke, et al. Standards Track [Page 7] RFC 5323 WebDAV SEARCH November 2008

 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.
 SEARCH is a safe method; it does not have any significance other than
 executing a query and returning a query result (see [RFC2616],
 Section 9.1.1).

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.  Any HTTP resource may
 function as search arbiter.  It is not a new type of resource (in the
 sense of DAV:resourcetype as defined in [RFC4918], Section 15.9), nor
 does it have to be a WebDAV-compliant resource.
 The SEARCH method defines no relationship between the arbiter and the
 scope of the search; rather, the particular query grammar used in the
 query defines the relationship.  For example, a query grammar may
 force the Request-URI to correspond exactly to the search scope.

2.2.2. The Request Body

 The server MUST process a text/xml or application/xml request body,
 and MAY process request bodies in other formats.  See [RFC3023] for
 guidance on packaging XML in requests.
 Marshalling:
    If a request body with content type text/xml or application/xml is
    included, it MUST be either a DAV:searchrequest or a DAV:query-
    schema-discovery XML element.  Its single child element identifies
    the query grammar.
    For DAV:searchrequest, the definition of search criteria, the
    result record, and any other details needed to perform the search
    depend on the individual search grammar.
    For DAV:query-schema-discovery, the semantics is defined in
    Section 4.

Reschke, et al. Standards Track [Page 8] RFC 5323 WebDAV SEARCH November 2008

 Preconditions:
    (DAV:search-grammar-discovery-supported): when an XML request body
    is present and has a DAV:query-schema-discovery document element,
    the server MUST support the query schema discovery mechanism
    described in Section 4.
    (DAV:search-grammar-supported): when an XML request body is
    present, the search grammar identified by the document element's
    child element must be a supported search grammar.
    (DAV:search-multiple-scope-supported): if the SEARCH request
    specified multiple scopes, the server MUST support this optional
    feature.
    (DAV:search-scope-valid): the supplied search scope must be valid.
    There can be various reasons for a search scope to be invalid,
    including unsupported URI schemes and communication problems.
    Servers MAY add [RFC4918] compliant DAV:response elements as
    content to the condition element indicating the precise reason for
    the failure.

2.3. The Successful 207 (Multistatus) Response

 If the server returns 207 (Multistatus), then the search proceeded
 successfully, and the response MUST use the WebDAV multistatus format
 ([RFC4918], Section 13).  The results of this method SHOULD NOT be
 cached.
 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.
    Note: the WebDAV multistatus format requires at least one DAV:
    response child element.  This specification relaxes that
    restriction so that empty results can be represented.
 Note that for each matching resource found, there may be multiple
 URIs within the search scope mapped to it.  In this case, a server
 SHOULD report only one of these URIs.  Clients can use the live
 property DAV:resource-id, defined in Section 3.1 of [WEBDAV-BIND] to
 identify possible duplicates.

2.3.1. 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

Reschke, et al. Standards Track [Page 9] RFC 5323 WebDAV SEARCH November 2008

 it does so, the reply MUST use status code 207, return a DAV:
 multistatus response body, and indicate a status of 507 (Insufficient
 Storage) for the search arbiter URI.  It SHOULD include the partial
 results.
 When a result set is truncated, there may be many more resources that
 satisfy the search criteria but that were not examined.
 If partial results are included and the client requested an ordered
 result set in the original request, then any partial results that are
 returned MUST be ordered as the client directed.
 Note that the partial results returned MAY be any subset of the
 result set that would have satisfied the original query.

2.3.2. Extending the PROPFIND Response

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

2.3.3. 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 natural-language-query in
 the XML namespace "http://example.com/foo".  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.
 >> Request:
 SEARCH / HTTP/1.1
 Host: example.org
 Content-Type: application/xml; charset="utf-8"
 Content-Length: 252
 <?xml version="1.0" encoding="UTF-8"?>
 <D:searchrequest xmlns:D="DAV:" xmlns:F="http://example.com/foo">
   <F:natural-language-query>
     Find the locations of good Thai restaurants in Los Angeles
   </F:natural-language-query>
 </D:searchrequest>

Reschke, et al. Standards Track [Page 10] RFC 5323 WebDAV SEARCH November 2008

 >> Response:
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: 429
 <?xml version="1.0" encoding="UTF-8"?>
 <D:multistatus xmlns:D="DAV:"
    xmlns:R="http://example.org/propschema">
   <D:response>
     <D:href>http://siamiam.example/</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:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
   </D:response>
 </D:multistatus>

2.3.4. Example: Result Set Truncation

 In the example below, the server returns just two results, and then
 indicates that the result is truncated by adding a DAV:response
 element for the search arbiter resource with 507 (Insufficient
 Storage) status.
 >> Request:
 SEARCH / HTTP/1.1
 Host: example.net
 Content-Type: text/xml; charset="utf-8"
 Content-Length: xxx
  ... the query goes here ...

Reschke, et al. Standards Track [Page 11] RFC 5323 WebDAV SEARCH November 2008

 >> Response:
 HTTP/1.1 207 Multistatus
 Content-Type: text/xml; charset="utf-8"
 Content-Length: 640
 <?xml version="1.0" encoding="utf-8"?>
 <D:multistatus xmlns:D="DAV:">
   <D:response>
     <D:href>http://www.example.net/sounds/unbrokenchain.au</D:href>
     <D:status>HTTP/1.1 200 OK</D:status>
   </D:response>
   <D:response>
     <D:href>http://tech.mit.example/arch96/photos/Lesh1.jpg</D:href>
     <D:status>HTTP/1.1 200 OK</D:status>
   </D:response>
   <D:response>
     <D:href>http://example.net</D:href>
     <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
     <D:responsedescription xml:lang="en">
        Only first two matching records were returned
     </D:responsedescription>
   </D:response>
 </D:multistatus>

2.4. Unsuccessful Responses

 If a SEARCH request could not be executed or the attempt to execute
 it resulted in an error, the server MUST indicate the failure with an
 appropriate status code and SHOULD add a response body as defined in
 Section 1.6 of [RFC3253].  Unless otherwise stated, condition
 elements are empty; however, specific condition elements MAY include
 additional child elements that describe the error condition in more
 detail.

2.4.1. Example of an Invalid Scope

 In the example below, a request failed because the scope identifies a
 HTTP resource that was not found.

Reschke, et al. Standards Track [Page 12] RFC 5323 WebDAV SEARCH November 2008

 >> Response:
 HTTP/1.1 409 Conflict
 Content-Type: text/xml; charset="utf-8"
 Content-Length: 275
 <?xml version="1.0" encoding="UTF-8"?>
 <d:error xmlns:d="DAV:">
   <d:search-scope-valid>
     <d:response>
       <d:href>http://www.example.com/X</d:href>
       <d:status>HTTP/1.1 404 Object Not Found</d:status>
     </d:response>
   </d:search-scope-valid>
 </d:error>

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:
 o  report SEARCH in the live property DAV:supported-method-set for
    all search arbiter resources, and
 o  support the live property DAV:supported-query-grammar-set as
    defined in Section 3.3.

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].

Reschke, et al. Standards Track [Page 13] RFC 5323 WebDAV SEARCH November 2008

 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 Section 10.1 of [RFC4918]>
 (This grammar uses the augmented BNF format defined in Section 2.1 of
 [RFC2616].)
 The DASL response header indicates server support for query grammars
 in the OPTIONS method.  The value is a list of URIs that indicate the
 types of supported grammars.  Note that although the URIs 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).
    Note: this header field value is defined as a comma-separated list
    ([RFC2616], Section 4.2); thus, grammar URIs can appear in
    multiple header instances, separated by commas, or both.
 For example:
 DASL: <http://foobar.example/syntax1>,
       <http://akuma.example/syntax2>, <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 -->

Reschke, et al. Standards Track [Page 14] RFC 5323 WebDAV SEARCH November 2008

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 servers supporting WebDAV SEARCH 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>, <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: 165
 <?xml version="1.0" encoding="UTF-8" ?>
 <propfind xmlns="DAV:">
   <prop>
     <supported-query-grammar-set/>
     <supported-method-set/>
   </prop>
 </propfind>

Reschke, et al. Standards Track [Page 15] RFC 5323 WebDAV SEARCH November 2008

 >> Response:
 HTTP/1.1 207 Multi-Status
 Content-Type: text/xml; charset="utf-8"
 Content-Length: 1349
 <?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>

Reschke, et al. Standards Track [Page 16] RFC 5323 WebDAV SEARCH November 2008

 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 an
 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 be 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

Reschke, et al. Standards Track [Page 17] RFC 5323 WebDAV SEARCH November 2008

 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 a DAV:query-schema-discovery element.
    <!ELEMENT query-schema-discovery ANY>
    <!-- ANY value: XML element specifying the query grammar
                    and the scope -->
    The response body takes the form of a DAV:multistatus element
    ([RFC4918], Section 13), where DAV:response is extended to hold
    the returned query grammar inside a DAV:query-schema container
    element.
    <!ELEMENT response (href, status, 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; charset="utf-8"
 Content-Length: 258
 <?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>

Reschke, et al. Standards Track [Page 18] RFC 5323 WebDAV SEARCH November 2008

 >> Response:
 HTTP/1.1 207 Multistatus
 Content-Type: application/xml; charset="utf-8"
 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:
 o  DAV:select provides the result record definition.
 o  DAV:from defines the scope.
 o  DAV:where defines the criteria.
 o  DAV:orderby defines the sort order of the result set.
 o  DAV:limit provides constraints on the query as a whole.

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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 -->

Reschke, et al. Standards Track [Page 20] RFC 5323 WebDAV SEARCH November 2008

 <!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) #IMPLIED>
 <!ELEMENT lte           (prop, (literal|typed-literal)) >
 <!ATTLIST lte           caseless   (yes|no) #IMPLIED>
 <!ELEMENT gt            (prop, (literal|typed-literal)) >
 <!ATTLIST gt            caseless   (yes|no) #IMPLIED>
 <!ELEMENT gte           (prop, (literal|typed-literal)) >
 <!ATTLIST gte           caseless   (yes|no) #IMPLIED>
 <!ELEMENT eq            (prop, (literal|typed-literal)) >
 <!ATTLIST eq            caseless   (yes|no) #IMPLIED>
 <!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) #IMPLIED>
 <!ELEMENT contains      (#PCDATA)>

Reschke, et al. Standards Track [Page 21] RFC 5323 WebDAV SEARCH November 2008

 <!-- "orderby" element -->
 <!ELEMENT orderby       (order+) >
 <!ELEMENT order         ((prop | score), (ascending | descending)?)>
 <!ATTLIST order         caseless   (yes|no) #IMPLIED>
 <!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 sorted ascending by size.
 <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>

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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 Section 14 of [RFC4918].

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 reference ([RFC3986], Section 4.1) 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 server supports WebDAV Redirect Reference Resources
 ([RFC4437]) and the search scope contains a redirect reference
 resource, then 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 (see Section 2.2.2,
 precondition DAV:search-scope-valid).

5.4.1. Relationship to the Request-URI

 If the DAV:scope element is a URI ([RFC3986], Section 3), the scope
 is exactly that URI.
 If the DAV:scope element is a relative reference ([RFC3986], Section
 4.2), the scope is taken to be relative to the Request-URI.

Reschke, et al. Standards Track [Page 23] RFC 5323 WebDAV SEARCH November 2008

5.4.2. Scope

 A Scope can be an arbitrary URI reference.
 Servers, of course, may support only particular scopes.  This may
 include limitations for particular schemes such as "http:" or "ftp:"
 or certain URI namespaces.  However, WebDAV-compliant search arbiters
 minimally SHOULD support scopes that match their own URI.

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 Section
 10.2 of [RFC2616]) 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 not NULL.

Reschke, et al. Standards Track [Page 24] RFC 5323 WebDAV SEARCH November 2008

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 xmlns:d='DAV:'>
   <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 of type "image/gif" over
 4K in size.
 <D:where xmlns:D='DAV:'>
   <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>

Reschke, et al. Standards Track [Page 25] RFC 5323 WebDAV SEARCH November 2008

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 (Section 5.18).

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 xmlns:d='DAV:' xmlns:r='http://example.com/ns'>
   <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.

Reschke, et al. Standards Track [Page 26] RFC 5323 WebDAV SEARCH November 2008

 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
 (Section 5.18).

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 (Section 5.18).

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 [RFC4918], clients SHOULD NOT specify the attribute
 "xml:space" (Section 2.10 of [XML]) to override this behavior.
 In comparisons, the contents of DAV:literal SHOULD be treated as
 string, with the following exceptions:
 o  when operand for a comparison with a DAV:getcontentlength
    property, it SHOULD be treated as an unsigned integer value (the
    behavior for values not in this format is undefined),
 o  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 (see
    Section 15.1 of [RFC4918]; the behavior of values not in this
    format is undefined),
 o  when operand for a comparison with a property for which the type
    is known and when compatible with that type, it MAY be treated
    according to this type.

Reschke, et al. Standards Track [Page 27] RFC 5323 WebDAV SEARCH November 2008

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
 Section 2.6.1 of [XS1].  If the type is not specified, it defaults to
 "xs:string".
 A server MUST reject a request using an unknown type with a status of
 422 (Unprocessable Entity).  It SHOULD reject a request if the value
 provided in DAV:typed-literal cannot be cast to the specified type.
 The comparison evaluates to UNKNOWN if the property value cannot 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":
                       +-----+----------------+
                       | URI | property 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:integer, 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"

Reschke, et al. Standards Track [Page 28] RFC 5323 WebDAV SEARCH November 2008

 and "/e" (the property either is undefined, or its value cannot be
 parsed as xs:integer).

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 Section 4.3 of [XPATH], "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>

Reschke, et al. Standards Track [Page 29] RFC 5323 WebDAV SEARCH November 2008

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 xmlns:d='DAV:' xmlns:x='http://example.com/ns'>
   <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.

Reschke, et al. Standards Track [Page 30] RFC 5323 WebDAV SEARCH November 2008

5.15.1. Syntax for the Literal Pattern

 pattern       = [wildcard] 0*( text [wildcard] )
 wildcard      = exactlyone / zeroormore
 text          = 1*( character / escapeseq )
 exactlyone    = "_"
 zeroormore    = "%"
 escapechar    = "\"
 escapeseq     = escapechar ( 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
 (Note that the ABNF above is defined in terms of Unicode code points
 ([UNICODE5]); when a query is transmitted as an XML document over
 WebDAV, these characters are typically encoded in UTF-8 or UTF-16.)
 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 xmlns:D='DAV:'>
   <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

Reschke, et al. Standards Track [Page 31] RFC 5323 WebDAV SEARCH November 2008

 against the text content of a resource, not against the 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 at the
 discretion of the server implementation.
 The following non-exhaustive list enumerates things that 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.
 Character canonicalization such as that done by the Unicode collation
 algorithm may or may not be applied.

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.

Reschke, et al. Standards Track [Page 32] RFC 5323 WebDAV SEARCH November 2008

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 xmlns:D='DAV:'>
   <D:contains>Peter Forsberg</D:contains>
 </D:where>
 The example below shows a search for resources that contain "Peter"
 and "Forsberg".
 <D:where xmlns:D='DAV:'>
   <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
 unsigned 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 SHOULD be those that order highest.

Reschke, et al. Standards Track [Page 33] RFC 5323 WebDAV SEARCH November 2008

5.18. The 'caseless' XML Attribute

 The "caseless" attribute allows clients to specify caseless matching
 behavior 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 ([UNICODE5]).
 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>
 <!ATTLIST opdesc             allow-pcdata (yes|no) #IMPLIED>
 <!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.

Reschke, et al. Standards Track [Page 34] RFC 5323 WebDAV SEARCH November 2008

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
 types are identified by an element name.  Where appropriate, a server
 SHOULD use the simple data types defined in [XS2].
 <!ELEMENT datatype ANY >

Reschke, et al. Standards Track [Page 35] RFC 5323 WebDAV SEARCH November 2008

 Examples from [XS2], Section 3:
               +----------------+---------------------+
               | Qualified name | Example             |
               +----------------+---------------------+
               | xs:boolean     | true, false, 1, 0   |
               | xs:string      | Foobar              |
               | xs:dateTime    | 1994-11-05T08:15:5Z |
               | 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 comparisons 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>

Reschke, et al. Standards Track [Page 36] RFC 5323 WebDAV SEARCH November 2008

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, contained in an DAV:opdesc element,
 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.
 The DAV:opdesc element MAY have a "allow-pcdata" attribute
 (defaulting to "no").  A value of "yes" indicates that the operator
 can contain character data, as it is the case with DAV:contains (see
 Section 5.16).  Definition of additional operators using this format
 is NOT RECOMMENDED.
 <operators xmlns='DAV:'>
   <opdesc>
     <like/><operand-property/><operand-literal/>
   </opdesc>
 </operators>

Reschke, et al. Standards Track [Page 37] RFC 5323 WebDAV SEARCH November 2008

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://ns.example.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:opdesc allow-pcdata="yes">
       <D:contains/>
     </D:opdesc>
   </D:operators>
 </D:basicsearchschema>
 This response lists four properties.  The data 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:contains
 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.

Reschke, et al. Standards Track [Page 38] RFC 5323 WebDAV SEARCH November 2008

6. Internationalization Considerations

 Properties may be language-tagged using the xml:lang attribute (see
 [RFC4918], Section 4.3).  The optional operators DAV:language-defined
 (Section 5.12.1) and DAV:language-matches (Section 5.12.2) allow the
 expression of 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 ([RFC2616] and WebDAV ([RFC4918])
 also apply to DASL.  In addition, this section will include security
 risks inherent in the search and retrieval of resource properties and
 content.
 A query MUST NOT allow clients to retrieve information that wouldn't
 have been available through the GET or PROPFIND methods in the first
 place.  In particular:
 o  Query constraints on WebDAV properties for which the client does
    not have read access need to be evaluated as if the property did
    not exist (see Section 5.5.3).
 o  Query constraints on content (as with DAV:contains, defined in
    Section 5.16) for which the client does not have read access need
    to be evaluated as if a GET would return a 4xx status code.
 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.

Reschke, et al. Standards Track [Page 39] RFC 5323 WebDAV SEARCH November 2008

 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 that 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 that 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 Section 21 of [RFC4918]
 for XML elements.

9.1. HTTP Headers

 This document specifies the HTTP header listed below, which has been
 added to the permanent HTTP header registry defined in [RFC3864].

9.1.1. DASL

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

Reschke, et al. Standards Track [Page 40] RFC 5323 WebDAV SEARCH November 2008

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, Surendra
 Reddy, and Judith Slein (see <http://www.webdav.org/dasl/> for the
 working group's web site,
 <http://purl.org/NET/webdav/dasl-references/reqs> for a requirements
 document, and
 <http://purl.org/NET/webdav/dasl-references/dasl-protocol-00> for an
 early version of the specification).

11. Acknowledgements

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

12. References

12.1. Normative References

 [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., Frystyk, H.,
                Masinter, L., Leach, P., and T. Berners-Lee,
                "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616,
                June 1999.
 [RFC3023]      Murata, 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 (Web
                Distributed Authoring and Versioning)", 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.
 [RFC3986]      Berners-Lee, T., Fielding, R., and L. Masinter,
                "Uniform Resource Identifier (URI): Generic Syntax",
                STD 66, RFC 3986, January 2005.

Reschke, et al. Standards Track [Page 41] RFC 5323 WebDAV SEARCH November 2008

 [RFC4918]      Dusseault, L., Ed., "HTTP Extensions for Web
                Distributed Authoring and Versioning (WebDAV)",
                RFC 4918, June 2007.
 [RFC5234]      Crocker, D., Ed. and P. Overell, "Augmented BNF for
                Syntax Specifications: ABNF", STD 68, RFC 5234,
                January 2008.
 [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

 [BCP47]        Phillips, A. and M. Davis, "Matching of Language
                Tags", BCP 47, RFC 4647, September 2006.
 [RFC3864]      Klyne, G., Nottingham, M., and J. Mogul, "Registration
                Procedures for Message Header Fields", BCP 90,
                RFC 3864, September 2004.
 [RFC4437]      Whitehead, J., Clemm, G., and J. Reschke, Ed., "Web
                Distributed Authoring and Versioning (WebDAV) Redirect
                Reference Resources", RFC 4437, March 2006.

Reschke, et al. Standards Track [Page 42] RFC 5323 WebDAV SEARCH November 2008

 [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.
 [UNICODE5]     The Unicode Consortium, "The Unicode Standard -
                Version 5.0", Addison-Wesley , November 2006,
                <http://www.unicode.org/versions/Unicode5.0.0/>.
                ISBN 0321480910 [1]
 [WEBDAV-BIND]  Clemm, G., Crawford, J., Reschke, J., Ed., and J.
                Whitehead, "Binding Extensions to Web Distributed
                Authoring and Versioning (WebDAV)", October 2008.

URIs

 [1]  <urn:isbn:0321480910>

Reschke, et al. Standards Track [Page 43] RFC 5323 WebDAV SEARCH November 2008

Appendix 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

Reschke, et al. Standards Track [Page 44] RFC 5323 WebDAV SEARCH November 2008

 UNKNOWN and FALSE = FALSE
 UNKNOWN and UNKNOWN = UNKNOWN
 UNKNOWN or TRUE = TRUE
 UNKNOWN or FALSE = UNKNOWN
 UNKNOWN or UNKNOWN = UNKNOWN

Appendix B. Candidates for Future Protocol Extensions

 This section summarizes issues that have been raised during the
 development of this specification, but for which no resolution could
 be found with the constraints in place.  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:
 o  Require server support for specific collations.
 o  Require that the server can advertise which collations it
    supports.
 o  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" ([RFC4790]).
 2.  "XQuery 1.0 and XPath 2.0 Functions and Operators" ([XPATHFUNC],
     Section 7.3.1).

Reschke, et al. Standards Track [Page 45] RFC 5323 WebDAV SEARCH November 2008

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. Diagnostics for Unsupported Queries

 There are many reasons why a given query may not be supported by a
 server.  Query Schema Discovery (Section 4) can be used to discover
 some constraints, but not all.
 Future revisions should consider the introduction of specific
 condition codes ([RFC4918], Section 16) to these situations.

B.4. Language Matching

 Section 5.12.2 defines language matching in terms of the XPath "lang"
 function ([XPATH], Section 4.3).  Future revisions should consider
 building on [BCP47] instead.

B.5. 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.6. 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.7. 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
 instance, using the DAV:limit element defined in Section 5.17).

Reschke, et al. Standards Track [Page 46] RFC 5323 WebDAV SEARCH November 2008

 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.

B.8. Search Scope Discovery

 Given a Search Arbiter resource, there's currently no way to discover
 programmatically the supported sets of search scopes.  Future
 revisions of this specification could specify a scope discovery
 mechanism, similar to the Query Schema Discovery defined in
 Section 4.

Index

 C
    caseless attribute  26-27, 34
    Condition Names
       DAV:search-grammar-discovery-supported (pre)  9
       DAV:search-grammar-supported (pre)  9
       DAV:search-multiple-scope-supported (pre)  9
       DAV:search-scope-valid (pre)  9
    Criteria  5
 D
    DAV:and  26
    DAV:ascending  26
    DAV:contains  31
    DAV:depth  23
    DAV:descending  26
    DAV:eq  27
       caseless attribute  27
    DAV:from  23
    DAV:gt  27
    DAV:gte  27
    DAV:include-versions  23
    DAV:is-collection  30
    DAV:is-defined  30
    DAV:language-defined  29
    DAV:language-matches  29
    DAV:like  30
    DAV:limit  33
    DAV:literal  27
    DAV:lt  27
    DAV:lte  27
    DAV:not  26
    DAV:nresults  33
    DAV:or  26

Reschke, et al. Standards Track [Page 47] RFC 5323 WebDAV SEARCH November 2008

    DAV:orderby  26
    DAV:scope  23
    DAV:score  32
       relationship to DAV:orderby  33
    DAV:search-grammar-discovery-supported precondition  9
    DAV:search-grammar-supported precondition  9
    DAV:search-multiple-scope-supported precondition  9
    DAV:search-scope-valid precondition  9
    DAV:select  23
    DAV:supported-query-grammar-set property  14
    DAV:typed-literal  28
    DAV:where  24
 M
    Methods
       SEARCH  7
 O
    OPTIONS method  13
       DASL response header  14
 P
    Properties
       DAV:supported-query-grammar-set  14
 Q
    Query  5
    Query Grammar  5
    Query Grammar Discovery  13
       using live property  13
       using OPTIONS  13
    Query Schema  5
 R
    Result  5
    Result Record  5
    Result Record Definition  5
    Result Set  5
    Result Set Truncation
       Example  10
 S
    Scope  6
    Search Arbiter  6
    SEARCH method  7
    Search Modifier  6
    Sort Specification  6

Reschke, et al. Standards Track [Page 48] RFC 5323 WebDAV SEARCH November 2008

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
 Mitrix, Inc.
 303 Twin Dolphin Drive, Suite 600-37
 Redwood City, CA  94065
 U.S.A.
 Phone: +1 408 500 1135
 EMail: Surendra.Reddy@mitrix.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
 IBM Corporation
 3565 Harbor Blvd.
 Costa Mesa, CA  92626
 U.S.A.
 Phone: +1 714 327 3403
 EMail: ababich@us.ibm.com

Reschke, et al. Standards Track [Page 49]

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