| Rfc | 5323 |
|---|
| Title | Web Distributed Authoring and Versioning (WebDAV) SEARCH |
|---|
| Author | J.
Reschke, Ed., S. Reddy, J. Davis, A. Babich |
|---|
| Date | November 2008 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
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.
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
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
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.
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.
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.
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).
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.
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
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>
>> 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 ...
>> 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.
>> 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].
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 -->
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>
>> 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>
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
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>
>> 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.
5.2. The DAV:basicsearch DTD
<!-- "basicsearch" element -->
<!ELEMENT basicsearch (select, from, where?, orderby?, limit?) >
<!-- "select" element -->
<!ELEMENT select (allprop | prop) >
<!-- "from" element -->
<!ELEMENT from (scope+) >
<!ELEMENT scope (href, depth, include-versions?) >
<!ELEMENT include-versions EMPTY >
<!-- "where" element -->
<!ENTITY % comp_ops "eq | lt | gt| lte | gte">
<!ENTITY % log_ops "and | or | not">
<!ENTITY % special_ops "is-collection | is-defined |
language-defined | language-matches">
<!ENTITY % string_ops "like">
<!ENTITY % content_ops "contains">
<!ENTITY % all_ops "%comp_ops; | %log_ops; | %special_ops; |
%string_ops; | %content_ops;">
<!ELEMENT where ( %all_ops; ) >
<!ELEMENT and ( %all_ops; )+ >
<!ELEMENT or ( %all_ops; )+ >
<!ELEMENT not ( %all_ops; ) >
<!ELEMENT lt (prop, (literal|typed-literal)) >
<!ATTLIST lt caseless (yes|no) #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)>
<!-- "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>
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.
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.
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>
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.
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.
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"
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>
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.
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
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.
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.
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.
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 >
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>
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>
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.
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.
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)
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.
[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.
[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>
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
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).
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).
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
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
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