WEBDAV DASL Working GroupJ. Reschke
Intended status: ExperimentalS. Reddy
Expires: December 2002Oracle
J. Davis
Intelligent Markets
A. Babich
June 2002


Status of this Memo

This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress”.

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

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

This Internet-Draft will expire in December 2002.

Copyright Notice

Copyright © The Internet Society (2002). All Rights Reserved.


1 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.

2 Distribution of this document is unlimited. Please send comments to the Distributed Authoring and Versioning (WebDAV) DASL working group at www-webdav-dasl@w3.org, which may be joined by sending a message with subject "subscribe" to www-webdav-dasl-request@w3.org.

3 Discussions of the WEBDAV DASL working group are archived at URL: http://www.w3.org/pub/WWW/Archives/Public/www-webdav-dasl/.

4 Distribution of this document is unlimited. Please send comments to the Distributed Authoring and Versioning (WebDAV) DASL mailing list at www-webdav-dasl@w3.org, which may be joined by sending a message with subject "subscribe" to www-webdav-dasl-request@w3.org. Discussions of the WebDAV DASL mailing list are archived at URL: http://www.w3.org/pub/WWW/Archives/Public/www-webdav-dasl/.

1. Introduction

1.1. DASL

5 This document defines WebDAV SEARCH, an application of HTTP/1.1 forming a lightweight search protocol to transport queries and result sets and allows clients to make use of server-side search facilities. It is based on the expired draft for WebDAV DASL [DASL]. [DASLREQ] describes the motivation for DASL.

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

7 DASL consists of:

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

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

1.2. Relationship to DAV

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

1.3. Terms

16 This draft uses the terms defined in [RFC2616], [RFC2518], and [DASLREQ].

1.4. Notational Conventions

17 The augmented BNF used by this document to describe protocol elements is exactly the same as the one described in Section 2.1 of [RFC2616]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [RFC2616], those rules apply to this document as well.

18 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].

19 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.

20 Note that this draft currently defines elements and properties in the WebDAV namespace "DAV:", which it shouldn't do as it isn't a work item of the WebDAV working group. The reason for this is the desire for some kind of backward compatibility to the expired DASL drafts and the assumption that the draft may become an official RFC submission of the WebDAV working group at a later point of time.

21 Similarily, 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. An Overview of DASL at Work

22 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 [RFC2518] PROPFIND response.

2. The SEARCH Method

2.1. Overview

27 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 [RFC2518] PROPFIND response.

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

2.2. The Request

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

2.2.1. The Request-URI

30 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 [RFC2518]), nor does it have to be a WebDAV-compliant resource.

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

2.2.2. The Request Body

32 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.

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

2.3. The DAV:searchrequest XML Element

<!ELEMENT searchrequest ANY >

34 The DAV:searchrequest XML element contains a single XML element that defines the query. The name of the query element defines the type of the query. The value of that element defines the query itself.

2.4. The Successful 207 (Multistatus) Response

35 If the server returns 207 (Multistatus), then the search proceeded successfully and the response MUST match that of a PROPFIND. The results of this method SHOULD NOT be cached.

36 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.

37 In addition, the server MAY include DAV:response items in the reply where the DAV:href element contains a URI that is not a matching resource, e.g. that of a scope or the query arbiter. Each such response item MUST NOT contain a DAV:propstat element, and MUST contain a DAV:status element (unless no property was selected).

2.4.1. Extending the PROPFIND Response

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

2.4.2. Example: A Simple Request and Response

39 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.

40 >> Request:

Host: ryu.com
Content-Type: application/xml
Content-Length: xxx

<?xml version="1.0" encoding="UTF-8"?>
<D:searchrequest xmlns:D="DAV:" xmlns:F="http://example.com/foo">
    Find the locations of good Thai restaurants in Los Angeles

41 >> Response:

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

<?xml version="1.0" encoding="UTF-8"?>
<D:multistatus xmlns:D="DAV:" xmlns:R="http://ryu.com/propschema">
        <R:location>259 W. Hollywood</R:location>

2.4.3. Example: Result Set Truncation

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

 I  result-truncation   (type: , status: open)
ldusseault@xythos.com2002-03-29 I believe the same response body that contains the first N <DAV:response> elements should also contain a *different* element stating that the results were incomplete and the result set was truncated by the server. There may also be a need to report that the results were incomplete and the result set was truncated at the choice of the client (isn't there a limit set in the client request?) That's important so the client knows the difference between receiving 10 results because there were >10 but only 10 were asked for, and receiving 10 results because there were only exactly 10 results and it just happens that 10 were asked for.
jrd3@alum.mit.edu2002-05-28 I agree that this could be useful, but I think this issue should be consolidated with issue JW5 (see below), which proposes that DASL basicsearch ought to have a way for client to request additional result sets. It should be moved because there is little or no value in allowing a client to distinguish between the case where "N results were requested, and there are exactly N available" and "N results were requested, and there are more than N available" if there is no way for client to get the next batch of results.

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

44 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.

45 Note that the partial results returned MAY be any subset of the result set that would have satisfied the original query.

46 >> Request:

Host: gdr.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

 ... the query goes here ...

47 >> Response:

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

<?xml version="1.0" encoding="utf-8"?>
<D:multistatus xmlns:D="DAV:">
      <D:status>HTTP/1.1 200 OK</D:status>
      <D:status>HTTP/1.1 200 OK</D:status>
    <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
    <D:responsedescription xml:lang="en">
       Only first two matching records were returned

2.5. Unsuccessful Responses

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

49 400 Bad Request. The query could not be executed. The request may be malformed (not valid XML for example). Additionally, this can be used for invalid scopes and search redirections.

50 422 Unprocessable entity. The query could not be executed. If a application/xml or text/xml request entity was provided, then it may have been well-formed but may have contained an unsupported or unimplemented query operator.

2.6. Invalid Scopes

2.6.1. Indicating an Invalid Scope

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

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

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

2.6.2. Example of an Invalid Scope

54 >> Response:

HTTP/1.1 400 Bad-Request
Content-Type: text/xml; charset="utf-8"   
Content-Length: xxx

<?xml version="1.0" encoding="UTF-8"?>

<d:multistatus xmlns:d="DAV:">
      <d:status>HTTP/1.1 404 Object Not Found</d:status>

3. Discovery of Supported Query Grammars

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

56 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.

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

3.1. The OPTIONS Method

60 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.

61 The client issues the OPTIONS method against a resource named by the Request-URI. This is a normal invocation of OPTIONS defined in [RFC2616].

62 If a resource supports the SEARCH method, then the server MUST list SEARCH in the OPTIONS response as defined by [RFC2616].

63 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

64 >> Response:

DASLHeader = "DASL" ":" Coded-URL-List
Coded-URL-List : Coded-URL [ "," Coded-URL-List ]
Coded-URL ; defined in section 9.4 of [RFC2518]

65 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 it's namespace name (a URI reference) and the element's local name).

66 This header MAY be repeated.

67 For example:

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

del-1. DAV:supported-search-grammar-set (protected)

68 This WebDAV property is required for any server supporting either [RFC3253] and/or [ACL] 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>

69 ANY value: a query grammar element type

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

70 This WebDAV property is required for any server supporting either [RFC3253] and/or [ACL] 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>

71 ANY value: a query grammar element type

3.4. Example: Grammar Discovery

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

73 >> Request:

OPTIONS /somefolder HTTP/1.1
Host: ryu.com

74 >> Response:

HTTP/1.1 200 OK
Date: Tue, 20 Jan 1998 20:52:29 GMT
DASL: <DAV:basicsearch>
DASL: <http://foo.bar.com/syntax1> 
DASL: <http://akuma.com/syntax2>

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

76 >> Request:

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

<?xml version="1.0" encoding="UTF-8" ?>
<propfind xmlns="DAV:">

77 >> 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:">
            <grammar><syntax1 xmlns="http://foo.bar.com" /></grammar>
            <grammar><syntax2 xmlns="http://akuma.com/"/></grammar>
          <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" />
      <status>HTTP/1.1 200 OK</status>

78 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

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

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

81 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.

 I  qsd-pseudo-property   (type: , status: closed)
julian.reschke@greenbytes.de2002-01-25 It would be nice to avoid the definition of a "pseudo" property just for this special use case.
julian.reschke@greenbytes.de2002-06-10 Proposal for alternate format at: (mailing list)
Associated changes in this document: 4.

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

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

del-2. The DAV:queryschema Property

<!ELEMENT queryschema ANY >

del-3. Example of query schema discovery

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

85 >> Request:

Host: recipes.com
Content-Type: application/xml
Content-Length: xxx

<?xml version="1.0"?>
<searchrequest xmlns="DAV:">

86 >> Response:

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

<?xml version="1.0"?>
<multistatus xmlns="DAV:">
            (See section "Query schema for DAV:basicsearch" for
            the actual contents) 
      <status>HTTP/1.1 200 OK</status>

4.1. Additional SEARCH semantics

87 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.

88 Marshalling:

  • The requst 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 RFC2518 DAV:multistatus element, 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>

92 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

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

94 >> Request:

Host: recipes.com
Content-Type: application/xml
Content-Length: xxx

<?xml version="1.0"?>
<query-schema-discovery xmlns="DAV:">

95 >> Response:

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

<?xml version="1.0"?>
<multistatus xmlns="DAV:">
    <status>HTTP/1.1 200 OK</status>
        (See section "Query schema for DAV:basicsearch" for
        the actual contents) 

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

5. The DAV:basicsearch Grammar

5.1. Introduction

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

98 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.
 I  JW24d   (type: , status: open)
ejw@ics.uci.edu2000-04-20 Where does xml:lang go in a query?
julian.reschke@greenbytes.de2002-02-28 What would be the *purpose* of putting xml:lang into a query?
jrd3@alum.mit.edu2002-05-28 The purpose is to allow one to express queries more precisely, e.g. to distinguish between the English word "hoop" (a circular object) and Dutch "hoop" (hope). Imagine a property that holds keywords for a resource. See 4.4 in http://www.ietf.org/rfc/rfc2518.txt, and 2.12 in http://www.w3.org/TR/REC-xml
julian.reschke@greenbytes.de2002-05-28 I think this would be an interesting feature, but it seems to be extremely hard to implement.
So assuming a query that
- the query specifies a language and
- be the text content of the property matches
The result will be:
1) true (match), if the property was stored with a matching xml:lang property (where the language tag matching rules would have to apply)
2) undefined if the property was stored without xml:lang
3) false otherwise
On the other hand if
- the query doesn't specify a language
the result will be:
4) undefined (at least according to the current wording).
1) requires that the query engine actually knows how to match language tags -- I'm not sure that everybody is willing to implement that.
2) is this desirable?
3) ok.
4) that seems to be wrong. If the query doesn't care, it should match, right?
Other problems:
- what is the language of a date-typed property?
- (sic!) where should xml:lang go into the query? There's no XML feature to undefine an xml:lang which is in scope, but there may be cases where this is needed.
On the other hand, if we drop this requirement, a client can still do a query and then process the result set -- the property elements in the response body will be reported with xml:lang (when persisted with language) anyway.
So I'd recommend to drop the feature. Defining string comparisons vs. collation sequences is hard enough.

5.2. The DAV:basicsearch DTD

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

<!ELEMENT select        (allprop | prop) >

<!ELEMENT from  (scope) >
<!ELEMENT scope (href, depth) >

<!ENTITY %comp_ops      "eq | lt | gt| lte | gte">
<!ENTITY %log_ops       "and | or | not">
<!ENTITY %special_ops   "is-collection | isdefined">
<!ENTITY %string_ops    "like">
<!ENTITY %content_ops   "contains">

<!ENTITY %all_ops       "%comp_ops; | %log_ops; | %special_ops; |
                            %string_ops; | %content_ops;">

<!ELEMENT where ( %all_ops; ) >

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

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

<!ELEMENT not   ( %all_ops; ) >

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

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

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

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

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

<!ELEMENT literal       (#PCDATA)>

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

<!ELEMENT contains      (#PCDATA)>

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

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

<!ELEMENT descending    EMPTY>

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

5.2.1. Example Query

105 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:">

5.3. DAV:select

106 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 [RFC2518].

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

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

109 The rules governing the status codes for each property match those of the PROPFIND method defined in [RFC2518].

5.4. DAV:from

110 DAV:from defines the query scope. This contains exactly one DAV:scope element. The scope element contains mandatory DAV:href and DAV:depth elements.

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

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

5.4.1. Relationship to the Request-URI

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

114 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

115 A Scope can be an arbitrary URI.

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

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

118 Example:

HTTP/1.1 400 Bad Request
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" encoding="UTF-8"?>
<d:multistatus xmlns:d="DAV:">
    <d:status>HTTP/1.1 502 Bad Gateway</d:status>

119 This example shows the response if there is a scope error. The response provides a Multistatus with a status for the scope. In this case, the scope cannot be reached because the server cannot search another server (502).

5.5. DAV:where

120 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.

 I  query-on-href   (type: , status: open)
julian.reschke@greenbytes.de2002-02-28DAV:href isn't a property, so it can't be used in queries. Is this a problem? Examples where DAV:displayname is queried instead seem to indicate that. A possible solution would be to allow DAV:href whereever DAV:prop is allowed in the where clause.

5.5.1. Use of Three-Valued Logic in Queries

121 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.

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

5.5.2. Handling Optional operators

123 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

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

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

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

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

5.5.4. Treatment of properties with mixed/element content

128 Comparisons of properties that do not have simple types (text-only content) is out-of-scope for DAV:basicsearch. For querying the DAV:resourcetype property, see Section 5.11.

5.5.5. Example: Testing for Equality

129 The example shows a single operator (DAV:eq) applied in the criteria.


5.5.6. Example: Relative Comparisons

130 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.


5.6. DAV:orderby

131 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.

132 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.

 I  null-ordering   (type: , status: open)
ameliac@us.ibm.com2002-02-20In the WebDAV SEARCH spec (5.6, DAV:orderby), it says that nulls sort low, to match SQL92. However, SQL92 and SQL99 both say "Whether a sort key value that is null is considered greater or less than a non-null value is implementation-defined, but all sort key values that are null shall either be considered greater than all non-null values or be considered less than all non-null values." (words taken from SQL99, 14.1 <declare cursor> General Rule 2)c), in reference to null handling for the <order by clause>. ) I would note that in 5.5.3 WebDAV SEARCH says nulls are less than all other values in a comparison, so the DAV:orderby matches that statement, it just gives an inaccurate reason.

133 In the context of the DAV:orderby element, null values are considered to collate before any actual (i.e., non null) value, including strings of zero length ( as in [SQL99]).

5.6.1. Comparing Natural Language Strings.

 I  language-comparison   (type: , status: open)
julian.reschke@greenbytes.de2002-03-03 XPath/XQuery (see draft, and open issue) specify string comparisons based on collations, not languages. I think we should adopt this. This would mean that "xml:lang" would be removed, and an optional attribute specifying the name of the collation is added.

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

135 The DAV:casesensitive "casesensitive" attribute may be used to indicate case-sensitivity for comparisons. Servers SHOULD do caseless matching as defined in [CaseMap].

5.6.2. Example of Sorting

136 This sort orders first by last name of the author, and then by size, in descending order, so that the largest works appear first.


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

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

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

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

5.8. DAV:eq

 I  JW24c   (type: , status: open)
ejw@ics.uci.edu2000-04-20How do string equality and language tag interact. Cross-language comparison should work at least when the two languages are dialects, e.g. en-us vs en-uk.
julian.reschke@greenbytes.de2002-01-28Proposal: strings match if and only if they match character by character.

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

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

5.9. DAV:lt, DAV:lte, DAV:gt, DAV:gte

 I  JW16b/JW24a   (type: , status: open)
ejw@ics.uci.edu2000-04-20Define how comparisons on strings work, esp for i18n.
Need policy statement about sort order in various national languages. (JW said "non-Latin" but it's an issue even in languages that use the latin char set.)

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

5.10. DAV:literal

 I  DB2/DB7   (type: , status: open)
ejw@ics.uci.edu2000-04-20Dates (HTTPDate in getlastmodified).
ejw@ics.uci.edu2000-04-20Agreement that it is OK to submit isodate to search HTTPDate (i.e., it's a marshalling issue only).
ejw@ics.uci.edu2000-04-20Booleans appear to be underspecified in the specification. How is a boolean tested, and what are the behavior of operators like less than, greater than, etc.
julian.reschke@greenbytes.de2002-01-28I think similar questions apply to booleans. Proposal: allow specification of the literal's type using XML Schema simple types, and declare that "both" WebDAV date types are compatible.
ABabich@filenet.com2002-01-29 The current DASL draft doesn't really have Booleans or any other data type. It's trying to skate on data types. Booleans could be tested using the "eq" and the combination "not eq", if you had well defined literals for TRUE and FALSE. With the current syntax, that is the way you would have to test a Boolean. Generally, Boolean values are not considered to be ordered, so "gt" etc. wouldn't apply. However, if the literal values of a Boolean were 1 and 0 for TRUE and FALSE (using the most commonly used convention of positive logic), then you would have an obvious ordering. 1 and 0 have the advantage of being language independent. You now see a lot of electronic and electro-mechanical devices (air conditioners, computers, etc.) with a "1/0" label on the power switch, "1" meaning "on", and "0" meaning "off".
SQL databases don't have Booleans. SQL doesn't control DASL, of course, but SQL databases are so widely used that they are important. The closest thing in SQL is a bit field. Each bit in a bit field is zero or 1.
So, why not close the issue by saying: DASL doesn't have data types. You can simulate Booleans by an integer data type, using 1 for "TRUE" and 0 for "FALSE".

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

144 White space in literal values is significant in comparisons. For consistency with [RFC2518], clients SHOULD NOT specify the attribute "xml:space" (section 2.10 of [XML]) to override this behaviour.

5.11. DAV:is-collection

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

146 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.

5.11.1. Example of DAV:is-collection

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

<where xmlns="DAV:">

5.12. DAV:isdefined

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

149 Example:

 I  isdefined-optional   (type: change, status: open)
julian.reschke@greenbytes.de2002-06-25 It's unclear why isdefined is an optional parameter.

150 The DAV:isdefined operator is optional.

5.13. DAV:like

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

152 The operator takes two arguments.

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

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

5.13.1. Syntax for the Literal Pattern

Pattern := [wildcard] 0*( text [wildcard] )
wildcard := exactlyone | zeroormore 
text := 1*( <character> | escapesequence )
exactlyone : = "?"
zeroormore := "%"
escapechar := "\"
escapesequence := "\" ( exactlyone | zeroormore | escapechar )
character: see section 2.2 of [XML]

155 The value for the literal is composed of wildcards separated by segments of text. Wildcards may begin or end the literal. Wildcards may not be adjacent.

156 The "?" wildcard matches exactly one character.

157 The "%" wildcard matches zero or more characters

158 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..

5.13.2. Example of DAV:like

159 This example shows how a client might use DAV:like to identify those resources whose content type was a subtype of image.


5.14. DAV:contains

 I  JW17/JW24b   (type: , status: open)
ejw@ics.uci.edu2000-04-205.13 should discuss handling of queries when character set differs.
Some text on handling character sets would be helpful.

160 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.

161 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.

162 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.

163 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.

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

5.14.1. Examples

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

166 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:contains>Peter Forsberg</D:contains>

167 The example below shows a search for resources that contain "Peter" and "Forsberg".


5.15. The DAV:limit XML Element

<!ELEMENT limit (nresults) >

168 The DAV:limit XML element contains requested limits from the client to limit the size of the reply or amount of effort expended by the server.

5.16. The DAV:nresults XML Element

<!ELEMENT nresults (#PCDATA)> ;only digits
 I  JW5   (type: , status: open)
ejw@ics.uci.edu1999-04-26On the topic of partial search results, DASL currently has no way for a client to request the next chunk of a set of search results. Since *every* search service I've interacted with on the Internet has a feature for returning the next set of search results, I really would expect this feature to be in DASL. An explanation for why this feature isn't present should be in the protocol specification if it is not going to be supported.
Martin.Wallmer@softwareag.com2002-03-08 of course this issue is legitim. However, as basicsearch should be as simple as possible, I tend to say out of scope as well. But perhaps this could be an optional feature (is it that, what you mean by extension to DAV:basicsearch)?
julian.reschke@greenbytes.de2002-03-08 Moved into DAV:basicsearch section, because this is a request for a specific query grammar feature.

169 The DAV:nresults XML element contains a requested maximum number of records to be returned in a reply. The server MAY disregard this limit. The value of this element is an integer.

del-4. The DAV:casesensitive XML attribute

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

171 The possible values for DAV:casesensitive are "1" or "0". The "1" value indicates case-sensitivity. The "0" value indicates case-insensitivity. The default value is server-specified. Case-insensitivity SHOULD implemented using caseless matching as defined in [CaseMap].

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

5.17. The "casesensitive" XML attribute


 I  case-insensitivity-name   (type: change, status: open)
julian.reschke@greenbytes.de2002-01-09The attribute probably should be renamed to "caseless".
 I  casesensitive-no-namespace   (type: change, status: closed)
julian.reschke@greenbytes.de2002-03-28Technically, this attribute is NOT in the DAV: namespace (otherwise it would need to be qualified).
The "casesensitive" attribute allows clients to specify case-sensitive or case-insensitive behavior for DAV:basicsearch operators.

174 The possible values for "casesensitive" are "1" or "0". The "1" value indicates case-sensitivity. The "0" value indicates case-insensitivity. The default value is server-specified. Case-insensitivity SHOULD implemented using caseless matching as defined in [CaseMap].

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

5.18. The DAV:score Property

<!ELEMENT score (#PCDATA)>

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

177 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.

 I  score-pseudo-property   (type: , status: open)
julian.reschke@greenbytes.de2002-02-28Shouldn't be done using a pseudo-property. Report it as child of DAV:propstat instead?

5.19. Query schema for DAV:basicsearch

178 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?,
<!ELEMENT operators          (opdesc*)>
<!ELEMENT opdesc             ANY>
<!ELEMENT operand-literal    EMPTY>
<!ELEMENT operand-property   EMPTY>

182 The DAV:properties element holds a list of descriptions of properties.

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

5.19.2. DAV:propdesc Element

184 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.

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

186 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

187 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. Datatypes are identified by an element name. Where appropriate, a server SHOULD use the simple datatypes defined in [XS2].

<!ELEMENT datatype ANY >

188 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

189 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>

190 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>

191 This element indicates that the property may appear in the DAV:select element.

5.19.6. The DAV:sortable Property Description

192 This element indicates that the property may appear in the DAV:orderby element.

<!ELEMENT sortable EMPTY>

5.19.7. The DAV:casesensitive Property Description

193 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 case sensitive. (The default is case insensitive.)

<!ELEMENT casesensitive EMPTY>

5.19.8. The DAV:operators XML Element

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

<operators xmlns='DAV:'>

5.19.9. Example of Query Schema for DAV:basicsearch

<D:basicsearchschema xmlns:D="DAV:"
      <D:prop><fstop xmlns="http://jennicam.org"/></D:prop>

195 This response lists four properties. The datatype 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:isdefined and DAV:like are supported.

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

6. Internationalization Considerations

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

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

199 Comparisons when this attribute differs have undefined order.

7. Security Considerations

 I  JW25/JW26   (type: , status: open)
ejw@ics.uci.edu2000-04-20In Security Considerations, copy XML considerations from webDAV spec.
ejw@ics.uci.edu2000-04-20Wouldn't it be better to just cite the XML document, so that if that document is updated, we won't have stale information?
ejw@ics.uci.edu2000-04-20In Security Considerations, mention privacy risks of queries.
julian.reschke@greenbytes.de2002-01-28Is this resolved?

200 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.

201 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.)

202 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

203 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.

204 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.

205 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

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

9. Authentication

207 Authentication mechanisms defined in WebDAV will also apply to DASL.

10. IANA Considerations

208 This document uses the namespace defined by [RFC2518] for XML elements. All other IANA considerations mentioned in [RFC2518] are also applicable to DASL.

12. Intellectual Property

210 To be supplied.

13. References

13.2. Informative References

Davis, M., “Case Mappings”, Unicode Techical Reports 21, February 2001, <http://www.unicode.org/unicode/reports/tr21>.
Reddy, S., Lowry, D., Reddy, S., Henderson, R., Davis, J., and A. Babich, “DAV Searching & Locating”, ID draft-dasl-protocol-00, July 1999, <http://www.webdav.org/dasl/protocol/draft-dasl-protocol-00.html>.
Davis, J., Reddy, S., and J. Slein, “Requirements for DAV Searching and Locating”, ID draft-dasl-requirements-01, February 1999, <http://www.webdav.org/dasl/requirements/draft-dasl-requirements-01.html>.
Milton, J., “Database Language SQL Part 2: Foundation (SQL/Foundation)”, ISO ISO/IEC 9075-2:1999 (E), July 1999.

Appendix A. Three-Valued Logic in DAV:basicsearch

216 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.).

217 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.

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

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

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

221 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.

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










Appendix B. Change Log

B.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.

B.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".



Authors' Addresses

Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Surendra Reddy
Oracle Corporation
600 Oracle Parkway, M/S 6op3
Redwoodshores, CA 94065
Phone: +1 650 506 5441
EMail: Surendra.Reddy@oracle.com
Jim Davis
Intelligent Markets
410 Jessie Street 6th floor
San Francisco, CA 94103
EMail: jrd3@alum.mit.edu
Alan Babich
FileNET Corp.
3565 Harbor Blvd.
Costa Mesa, CA 92626
Phone: +1 714 327 3403
EMail: ababich@filenet.com

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