Internet DRAFT - draft-dasl-protocol
draft-dasl-protocol
INTERNET-DRAFT Saveen Reddy,
Microsoft
draft-dasl-protocol-00.txt Dale Lowry, Novell
Surendra Reddy,
Oracle
Rick Henderson,
Netscape
Jim Davis, CourseNet
Alan Babich, Filenet
Expires December 24, 1999 June 24, 1999
DAV Searching & Locating
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
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Abstract
This document specifies a set of methods, headers, and content-types
composing DASL, an application of the HTTP/1.1 protocol to efficiently
search for DAV resources based upon a set of client-supplied criteria.
1. Introduction
1.1 DASL
This document defines DAV Searching & Locating (DASL), an application
of HTTP/1.1 forming a lightweight search protocol to transport queries
and result sets and allows clients to make use of server-side search
facilities. [DASLREQ] describes the motivation for DASL.
Reddy et al [Page 1]
DASL
DASL will minimize the complexity of clients so as to facilitate
widespread deployment of applications capable of utilizing the DASL
search mechanisms.
DASL consists of:
* the SEARCH method,
* the DASL response header,
* the DAV:searchrequest XML element,
* the DAV:queryschema property,
* the DAV:basicsearch XML element and query grammar, and
* the DAV:basicsearchschema XML element.
1.2 Relationship to DAV
DASL relies on the resource and property model defined by [WebDAV].
DASL does not alter this model. Instead, DASL allows clients to access
DAV-modeled resources through server-side search.
1.3 Terms
This draft uses the terms defined in [RFC2068], [WebDAV], and
[DASLREQ].
1.4 Notational Conventions
The augmented BNF used by this document to describe protocol elements
is exactly the same as the one described in Section 2.1 of [RFC2068].
Because this augmented BNF uses the basic production rules provided in
Section 2.2 of [RFC2068], those rules apply to this document as well.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.5 An Overview of DASL at Work
One can express the basic usage of DASL in the following steps:
* The client constructs a query using the DAV:basicsearch grammar.
* The client invokes the SEARCH method on a resource that will
perform the search (the search arbiter) and includes a text/xml
request entity that contains the query.
* The search arbiter performs the query.
* The search arbiter sends the results of the query back to the
client in the response. The server MUST send a text/xml entity
that matches the [WebDAV] PROPFIND response.
2. The SEARCH Method
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DASL
2.1 Overview
The client invokes the SEARCH method to initiate a server-side search.
The body of the request defines the query. The server MUST emit
text/xml entity matching the [WebDAV] PROPFIND response.
The SEARCH method plays the role of transport mechanism for the query
and the result set. It does not define the semantics of the query. The
type of the query defines the semantics.
2.2 The Request
The client invokes the SEARCH method on the resource named by the
Request-URI.
2.2.1 The Request-URI
The Request-URI identifies the search arbiter.
The SEARCH method defines no relationship between the arbiter and the
scope of the search, rather the particular query grammar used in the
query defines the relationship. For example, the FOO query grammar may
force the request-URI to correspond exactly to the search scope.
2.2.2 The Request Body
The server MUST process a text/xml or application/xml request body,
and MAY process request bodies in other formats. See [RFC 2376] for
guidance on packaging XML in requests.
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 > The DAV:searchrequest XML element
contains a single XML element that defines the query. The name of the
query element defines the type of the query. The value of that element
defines the query itself.
2.4 The Successful 207 (Multistatus) Response
If the server returns 207 (Multistatus), then the search proceeded
successfully and the response MUST match that of a PROPFIND.
There MUST be one DAV:response for each resource that matched the
search criteria. For each such response, the DAV:href element contains
the URI of the resource, and the response MUST include a DAV:propstat
element.
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DASL
In addition, the server MAY include DAV:response items in the reply where
the DAV:href element contains a URI that is not a matching resource,
e.g. that of a scope or the query arbiter. Each such response item
MUST NOT contain a DAV:propstat element, and MUST contain a DAV:status
. It SHOULD contain a DAV:responsedescription .
2.4.1 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.
2.4.1 Example: A Simple Request and Response
This example demonstrates the request and response framework. The
following XML document shows a simple (hypothetical) natural language
query. The name of the query element is FOO:natural-language-query,
thus the type of the query is FOO:natural-language-query. The actual
query is "Find the locations of good Thai restaurants in Los Angeles".
For this hypothetical query, the arbiter returns two properties for
each selected resource.SEARCH / HTTP/1.1
Host: ryu.com
Content-Type: text/xml
Connection: Close
Content-Length: 243
<?xml version="1.0"?>
<D:searchrequest xmlns:D = "DAV:" xmlns:F = "FOO:">
<F:natural-language-query>
Find the locations of good Thai restaurants in Los Angeles
</F:natural-language-query>
</D:searchrequest> >> ResponseHTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: 333
<?xml version="1.0"?>
<D:multistatus xmlns:D="DAV:" xmlns:F="FOO:"
xmlns:R="http://ryu.com/propschema">
<D:response>
<D:href>http://siamiam.com/</D:href>
<D:propstat>
<D:prop>
<R:location>259 W. Hollywood</R:location>
<R:rating><R:stars>4</R:stars></R:rating>
</D:prop>
</D:propstat>
</D:response>
</D:multistatus>
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2.5 Unsuccessful Responses
If an error occurred that prevented execution of the query, the server
MUST indicate the failure with the appropriate status code and SHOULD
include a DAV:multistatus element to point out errors associated with
scopes.
400 Bad Request. The query could not be executed. The request may be
malformed (not valid XML for example). Additionally, this can be used
for invalid scopes and search redirections.
422 Unprocessable entity. The query could not be executed. If a
text/xml request entity was provided, then it may have been valid
(well-formed) but may have contained an unsupported or unimplemented
query operator.
507 (Insufficient Storage). The query produced more results than the
server was willing to transmit. Partial results have been transmitted.
The server MUST send a body that matches that for 207, except that
there MAY exist resources that matched the search criteria for which
no corresponding DAV:response exists in the reply.
2.5.1 Example: Result Set Truncation
A server MAY limit the number of resources in a reply, for example to
limit the amount of resources expended in processing a query. If it
does so, the reply MUST use status code 507. 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.SEARCH / HTTP/1.1
Host: gdr.com
Content-Type: text/xml
Connection: Close
Content-Length: xxxxx
<?xml version="1.0"?>
<D:searchrequest xmlns:D="DAV:">
<D:basicsearch>
ą the query goes here ą
</D:basicsearch>
</D:searchrequest>>> Response
HTTP/1.1 507 Insufficient Storage
Content-Type: text/xml
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Content-Length: 738
<?xml version="1.0"?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.gdr.com/sounds/unbrokenchain.au</D:href>
<D:propstat>
<D:prop/>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://tech.mit.edu/archive96/photos/Lesh1.jpg</D:href>
<D:propstat>
<D:prop/>
<D:status>HTTP/1.1 200 OK</D:status>
<D:/propstat>
</D:response>
<D:response>
<D:href>http://gdr.com</href>
<D:status>HTTP/1.1 507 Insufficient Storage</D:status>
<D:responsedescription>
Only first two matching records were returned
</D:responsedescription>
</D:response>
</D:multistatus>
2.6 Invalid Scopes & Search Redirections
2.6.1 Indicating an Invalid Scope
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".
To indicate an invalid scope, the server MUST respond with a 400 (Bad
Request).
The response includes a text/xml body with a DAV:multistatus element.
Each DAV:resource 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
HTTP/1.1 400 Bad-Request
Content-Type: text/xml
Content-Length: xxxxx
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<?xml version="1.0" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.foo.com/X</d:href>
<d:status>HTTP/1.1 404 Object Not Found</d:status>
<d:scopeerror/>
</d:response>
</d:multistatus>
2.6.3 Redirections
As described above, a server can indicate only that the scope is
invalid. Some search arbiters may be able to indicate that other
search arbiters exist for that scope.
In this case, the server MUST:
(1) include the DAV:scopeerror element
(2) include the DAV:status element for that scope. The value of this
element MUST be a 303 (See Other) response.
(3) include the DAV:redirectarbiter element for each arbiter the
client should use for the redirect. The value of this element is the
URI of the arbiter to use. Multiple DAV:redirectarbiter elements are
allowed.
2.6.4 Example of a Search Redirection
HTTP/1.1 400 Bad-Request
Content-Type: text/xml
Content-Length: xxxxx
<?xml version="1.0" ?>
<?xml:namespace ns="DAV:" prefix="d" ?>
<d:multistatus>
<d:response>
<d:href>http://www.foo.com/X</d:href>
<d:status>HTTP/1.1 303 See Other</d:status>
<d:scopeerror/>
<d:redirectarbiter>http://bar.com/B</d:redirectarbiter>
<d:redirectarbiter>http://baz.com/B</d:redirectarbiter>
</d:response>
</d:multistatus>
2.6.5 Syntax for DAV:scopeerror
<!ELEMENT scopeerror EMPTY>
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2.6.6 Syntax for DAV:redirectarbiter
<!ELEMENT redirectarbiter (#PCDATA)> The contents must
be a URL.
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.
3.1 The OPTIONS Method
The OPTIONS method allows the client to discover if a resource
supports the SEARCH method and to determine the list of search
grammars supported for that resource.
The client issues the OPTIONS method against a resource named by the
Request-URI. This is a normal invocation of OPTIONS defined in
[RFC2068].
If a resource supports the SEARCH method, then the server MUST list
SEARCH in the OPTIONS response as defined by [RFC2068].
DASL servers MUST include the DASL header in the OPTIONS response.
This header identifies the search grammars supported by that resource.
3.2 The DASL Response Header
DASLHeader = "DASL" ":" Coded-URL-List
Coded-URL-List : Coded-URL [ "," Coded-URL-List ]
Coded-URL ; defined in section 9.4 of [WEBDAV] The DASL response
header indicates server support for a query grammar in the OPTIONS
method. The value is a URI that indicates the type of grammar. This
header MAY be repeated.
For example:DASL: <http://foo.bar.com/syntax1>
DASL: <http://akuma.com/syntax2>
DASL: <FOO:natural-language-query>
3.3 Example: Grammar Discovery
This example shows that the server supports search on the /somefolder
resource with the query grammars: DAV:basicsearch,
http://foo.bar.com/syntax1 and http://akuma.com/syntax2 . Note that
every server MUST support DAV:basicsearch .
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>>Request
OPTIONS /somefolder HTTP/1.1
Connection: Close
Host: ryu.com >> ResponseHTTP/1.1 200 OK
Date: Tue, 20 Jan 1998 20:52:29 GMT
Connection: close
Accept-Ranges: none
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE,
MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, SEARCH
Public: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE,
MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, SEARCH
DASL: <DAV:basicsearch>
DASL: <http://foo.bar.com/syntax1>
DASL: <http://akuma.com/syntax2>
4. Query Schema Discovery: QSD
Servers MAY support the discovery of the schema for a query grammar.
The DASL response header provides means for clients to discover the
set of query grammars supported by a resource. This alone is not
sufficient information for a client to generate a query. For example,
the DAV:basicsearch grammar defines a set of queries consisting of a
set of operators applied to a set of properties and values, but the
grammar itself does not specify which properties may be used in the
query. QSD for the DAV:basicsearch grammar allows a client to discover
the set of properties that are searchable, selectable, and sortable.
Moreover, although the DAV:basicsearch grammar defines a minimal set
of operators, it is possible that a resource might support additional
operators in a query. For example, a resource might support a optional
operator that can be used to express content-based queries in a
proprietary syntax. QSD allows a client to discover these operators
and their syntax. The set of discoverable quantities will differ from
grammar to grammar, but each grammar can define a means for a client
to discover what can be discovered.
In general, the schema for a given query grammar depends on both the
resource (the arbiter) and the scope. A given resource might have
access to one set of properties for one potential scope, and another
set for a different scope. For example, consider a server able to
search two distinct collections, one holding cooking recipes, the
other design documents for nuclear weapons. While both collections
might support properties such as author, title, and date, the first
might also define properties such as calories and preparation time,
while the second defined properties such as yield and applicable
patents. Two distinct arbiters indexing the same collection might also
have access to different properties. For example, the recipe
collection mentioned above might also indexed by a value-added server
that also stored the names of chefs who had tested the recipe. Note
also that the available query schema might also depend on other
factors, such as the identity of the principal conducting the search,
but these factors are not exposed in this protocol.
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DASL
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.
The query schema for DAV:basicsearch is defined in section 5.19.
4.1 The DAV:queryschema Property
<!ELEMENT queryschema ANY >
4.1.1 Example of query schema discovery
In this example, the arbiter is recipes.com, the grammar is
DAV:basicsearch , the scope is also recipes.com.SEARCH / HTTP/1.1
Host: recipes.com
Content-Type: application/xml
Connection: Close
Content-Length: xxx
<?xml version="1.0"?>
<D:searchrequest xmlns:D="DAV:" >
<D:basicsearch>
<D:select>
<D:queryschema/>
</D:select>
<D:from><D:scope><D:href>http://recipes.com</d:href></D:scope></D:from>
</D:basicsearch>
</D:searchrequest> Response:HTTP/1.1 207 Multistatus
Content-Type: application/xml
Content-Length: xxx
<?xml version="1.0"?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://recipes.com</D:href>
<D:propstat>
<D:prop>
<D:querygrammar>
<D:basicsearchschema>
See section 5.19.9 for actual contents
</D:basicsearchschema>
</D:querygrammar>
</D:prop>
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<D:status>HTTP/1.1 200 Okay</D:status>
</D:propstat>
</D:response>
</D:multistatus>
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 others grammars.
DAV:basicsearch has several components:
* DAV:select provides the result record definition.
* DAV:from defines the scope.
* DAV:where defines the criteria.
* DAV:orderby defines the sort order of the result set.
* DAV:limit provides constraints on the query as a whole.
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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 "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)>
<!ATTLIST literal xml:space (default|preserve) preserve >
<!ELEMENT isdefined (prop) >
<!ELEMENT like (prop, literal) >
<!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) >
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5.2.1 Example Query
This query retrieves the content length values for all resources
located under the server's "/container1/" URI namespace whose length
exceeds 10000.<d:searchrequest>
<d: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 [WebDAV].
If the value is DAV:allprop , the result record for a given resource
includes all the properties for that resource.
If the value is DAV:prop , then the result record for a given resource
includes only those properties named by the DAV:prop element. Each
property named by the DAV:prop element must be referenced in the
Multistatus response.
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The rules governing the status codes for each property match those of
the PROPFIND method defined in [WebDAV].
5.4 DAV:from
DAV:from defines the query scope. This contains exactly one DAV:scope
element. The scope element contains a mandatory DAV:href element and
an optional DAV:depth element.
DAV:href indicates the URI for a collection to use as a scope.
When the scope is a collection, if DAV:depth is "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
If the DAV:scope element is an absolute URI, the scope is exactly that
URI.
If the DAV:scope element is a relative URI, the scope is taken to be
relative to the request-URI.
5.4.2 Scope
A Scope can be an arbitrary URI.
Servers, of course, may support only particular scopes. This may
include limitations for particular schemes such as "http:" or "ftp:"
or certain URI namespaces.
If a scope is given that is not supported the server MUST respond with
a 400 status code that includes a Multistatus error. A scope in the
query appears as a resource in the response and must include an
appropriate status code indicating its validity with respect to the
search arbiter.
Example:HTTP/1.1 400 Bad Request
Content-Type: text/xml
Content-Length: 428
<?xml version="1.0" ?>
<d:multistatus xmlns:D="DAV:" xmlns:F="FOO:" >
<d:response>
<d:href>http://www.foo.com/scope1</d:href>
<d:status>HTTP/1.1 502 Bad Gateway</d:status>
</d:response>
</d:multistatus> This example shows the response if there is a scope
error. The response provides a Multistatus with a status for the
scope. In this case, the scope cannot be reached because the server
cannot search another server (502).
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5.5 DAV:where
DAV:where element defines the search condition for inclusion of
resources in the result set. The value of this element is an XML
element that defines a search operator that evaluates to one of the
Boolean truth values TRUE, FALSE, or UNKNOWN. The search operator
contained by DAV:where may itself contain and evaluate additional
search operators as operands, which in turn may contain and evaluate
additional search operators as operands, etc. recursively.
5.5.1 Use of Three-Valued Logic in Queries
Each operator defined for use in the where clause that returns a
Boolean value MUST evaluate to TRUE, FALSE, or UNKNOWN. The resource
under scan is included as a member of the result set if and only if
the search condition evaluates to TRUE.
Consult Appendix A for details on the application of three-valued
logic in query expressions.
5.5.2 Handling Optional operators
If a query provides an operator that is not supported by the server,
then the server MUST respond with a 422 (Unprocessable Entity) status
code.
5.5.3 Treatment of NULL Values
If a SEARCH PROPFIND for a property value would yield a 404 or 403
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 then" a string with length greater than zero.
The DAV:isdefined operator is defined to test if the value of a
property is NULL.
5.5.4 Example: Testing for Equality
The example shows a single operator ( DAV:eq ) applied in the
criteria.<d:where>
<d:eq>
<d:prop> <d:getcontentlength/> </d:prop>
<d:literal> 100 </d:literal>
</d:eq>
</d:where>
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5.5.5 Example: Relative Comparisons
The example shows a more complex operation involving several operators
( DAV:and , DAV:eq , DAV:gt ) applied in the criteria. This DAV:where
expression matches those resources that are "image/gifs" over 4K in
size.<D:where>
<D:and>
<D:eq>
<D:prop> <D:getcontenttype/> </D:prop>
<D:literal> image/gif </D:literal>
</D:eq>
<D:gt>
<D:prop> <D:getcontentlength/> </D:prop>
<D:literal> 4096 </D:literal>
</D:gt>
</D:and>
</D:where>
5.6 DAV: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 (as in ANSI standard SQL, [ANSISQL]).
5.6.1 Comparing Natural Language Strings.
Comparisons on strings take into account the language defined for that
property. Clients MAY specify the language using the xml:lang
attribute. If no language is specified either by the client or defined
for that property by the server or if a comparison is performed on
strings of two different languages, the results are undefined.
The DAV:casesensitive attribute may be used to indicate
case-sensitivity for comparisons.
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5.6.2 Example of Sorting
This sort orders first by last name of the author, and then by size,
in descending order, so that the largest works appear first.
<d:orderby>
<d:order>
<d:prop><r:lastname/></d:prop>
<d:ascending/>
</d:order>
<d:order>
<d:prop><d:getcontentlength/></d:prop>
<d:descending/>
</d:order>
</d:orderby>
5.7 Boolean Operators: DAV:and , DAV:or , and DAV:not
The DAV:and operator performs a logical AND operation on the
expressions it contains.
The DAV:or operator performs a logical OR operation on the values it
contains.
The DAV:not operator performs a logical NOT operation on the values it
contains.
5.8 DAV:eq
The DAV:eq operator provides simple equality matching on property
values.
The DAV:casesensitive attribute may be used with this element.
5.9 DAV:lt , DAV:lte , DAV:gt , DAV:gte
The DAV:lt , DAV:lte , DAV:gt , and DAV:gte operators provide
comparisons on property values, using less-than, less-than or equal,
greater-than, and greater-than or equal respectively. The
DAV:casesensitive attribute may be used with these elements.
5.10 DAV:literal
DAV:literal allows literal values to be placed in an expression.
Because white space in literal values is significant in comparisons,
DAV:literal makes use of the xml:space attribute to identify this
significance. The default value of this attribute for DAV:literal is
preserve. Consult section 2.10 of [XML] for more information on the
use of this attribute.
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5.11 DAV:isdefined
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.
Example:
<d:isdefined>
<d:prop><x:someprop/></d:prop>
</d:isdefined>
The DAV:isdefined operator is optional.
5.12 DAV:like
The DAV:like is an optional operator intended to give simple
wildcard-based pattern matching ability to clients.
The operator takes two arguments.
The first argument is a DAV:prop element identifying a single property
to evaluate.
The second argument is a DAV:literal element that gives the pattern
matching string.
5.12.1 Syntax for the Literal Pattern
Pattern := [wildcard] 0*( text [wildcard] )
wildcard := exactlyone | zeroormore
text := 1*( <octet> | escapesequence )
exactlyone : = "?"
zeroormore := "%"
escapechar := "\"
escapesequence := "\" ( exactlyone | zeroormore | escapechar ) The
value for the literal is composed of wildcards separated by segments
of text. Wildcards may begin or end the literal. Wildcards may not be
adjacent.
The "?" wildcard matches exactly one character.
The "%" wildcard matches zero or more characters
The "\" character is an escape sequence so that the literal can
include "?" and "%". To include the "\" character in the pattern, the
escape sequence "\\" is used..
5.12.2 Example of DAV:like
This example shows how a client might use DAV:like to identify those
resources whose content type was a subtype of image.<D:where>
<D:like>
<D:prop><D:getcontenttype/></D:prop>
<D:literal>image%</D:literal>
</D:like>
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</D:where>
5.13 DAV:contains
The DAV:contains operator is an optional operator that provides
content-based search capability. This operator implicitly searches
against the text content of a resource, not against content of
properties. The DAV:contains operator is intentionally not overly
constrained, in order to allow the server to do the best job it can in
performing the search.
The DAV:contains operator evaluates to a Boolean value. It evaluates
to TRUE if the content of the resource satisfies the search.
Otherwise, It evaluates to FALSE.
Within the DAV:contains XML element, the client provides a phrase: a
single word or whitespace delimited sequence of words. Servers MAY
ignore punctuation in a phrase. Case-sensitivity is left to the
server.
The following things may or may not be done as part of the search:
Phonetic methods such as "soundex" may or may not be used. Word
stemming may or may not be performed. Thesaurus expansion of words may
or may not be done. Right or left truncation may or may not be
performed. The search may be case insensitive or case sensitive. The
word or words may or may not be interpreted as names. Multiple words
may or may not be required to be adjacent or "near" each other.
Multiple words may or may not be required to occur in the same order.
Multiple words may or may not be treated as a phrase. The search may
or may not be interpreted as a request to find documents "similar" to
the string operand.
The DAV:score property is intended to be useful to rank documents
satisfying the DAV:contains operator.
5.13.1 Examples
The example below shows a search for the phrase "Peter Forsberg".
Depending on its support for content-based searching, a server MAY
treat this as a search for documents that contain the words "Peter"
and "Forsberg".<D:where>
<D:contains>Peter Forsberg</D:contains>
</D:where> The example below shows a search for resources that contain
"Peter" and "Forsberg".<D:where>
<D:and>
<D:contains>Peter</D:contains>
<D:contains>Forsberg</D:contains>
</D:and>
</D:where>
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5.14 The DAV:limit XML Element
<!ELEMENT limit (nresults) > The DAV:limit XML element contains
requested limits from the client to limit the size of the reply or
amount of effort expended by the server.
5.15 The DAV:nresults XML Element
<!ELEMENT nresults (#PCDATA)> ;only digits The DAV:nresults XML
element contains a requested maximum number of records to be returned
in a reply. The server MAY disregard this limit. The value of this
element is an integer.
5.16 The DAV:casesensitive XML attribute
The DAV:casesensitive attribute allows clients to specify
case-sensitive or case-insensitive behavior for DAV:basicsearch
operators.
The possible values for DAV:casesensitive are "1" or "0". The "1"
value indicates case-sensitivity. The "0" value indicates
case-insensitivity. The default value is server-specified.
Support for the DAV:casesensitive is optional. A server should respond
with an error 422 if the DAV:casesensitive attribute is used but
cannot be supported.
5.17 The DAV:score Property
<!ELEMENT score (#PCDATA)> The DAV:score XML element is a synthetic
property whose value is defined only in the context of a query result
where the server computes a score, e.g. based on relevance. It may be
used in DAV:select or DAV: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).
Clients should note that, in general, it is not meaningful to compare
the numeric values of scores from two different queries unless both
were executed by the same underlying search system on the same
collection of resources.
5.18 The DAV:iscollection Property
<!ELEMENT iscollection (#PCDATA)> The DAV:iscollection XML element is
a synthetic property whose value is defined only in the context of a
query.
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The property is TRUE (the literal string "1") of a resource if and only
if a PROPFIND of the DAV:resourcetype property for that resource would
contain the DAV:collection XML element. The property is FALSE (the
literal string "0") otherwise.
Rationale : This property is provided in lieu of defining generic
structure queries, which would suffice for this and for many more
powerful queries, but seems inappropriate to standardize at this time.
5.18.1 Example of DAV:iscollection
This example shows a search criterion that picks out all and only the
resources in the scope that are collections.<D:where>
<D:eq>
<D:prop><D:iscollection></D:prop>
<D:literal>1<D:literal>
</D:eq>
</D:where>
5.19 QuerySchema 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 optional operators defined by the resource.
5.19.1 DTD for DAV:basicsearch QSD
<!ELEMENT basicsearchschema (properties, operators)>
<!ELEMENT properties (propdesc*)>
<!ELEMENT propdesc (prop, ANY)>
<!ELEMENT operators (opdesc*)>
<!ELEMENT opdesc ANY>
<!ELEMENT operand_property EMPTY>
<!ELEMENT operand_literal EMPTY> The DAV:properties element
holds a list of descriptions of properties.
The DAV:operators element describes the optional operators that may be
used in a DAV:where element.
5.19.2 DAV:propdesc Element
Each instance of a DAV:propdesc element describes the property or
properties in the DAV:prop element it contains. All subsequent
elements are descriptions that apply to those properties. All
descriptions are optional and may appear in any order. Servers SHOULD
support all the descriptions defined here, and MAY define others.
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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.
5.19.3 The DAV:datatype Property Description
The DAV:datatype element contains a single XML element that provides a
hint about the domain of the property, which may be useful to a user
interface prompting for a value to be used in a query. The namespace
for expressing a DASL defined data type is
"urn:uuid:C2F41010-65B3-11d1-A29F-00AA00C14882/".<!ELEMENT datatype
ANY > DASL defines the following data type elements: Name example
boolean 1, 0
string Foobar
dateTime.iso8601tz 1994-11-05T08:15:5Z
float .314159265358979E+1
int -259, 23
If the data type of a property is not given, then the data type
defaults to string.
5.19.4 The DAV:searchable Property Description
<!ELEMENT searchable EMPTY > If this element is
present, then the server MUST allow this property to appear within a
DAV:where element where an operator allows a property. Allowing a
search does not mean that the property is guaranteed to be defined on
every resource in the scope, it only indicates the server's
willingness to check.
5.19.5 The DAV:selectable Property Description
<!ELEMENT selectable EMPTY > This element indicates
that the property may appear in the DAV:select element.
5.19.6 The DAV:sortable Property Description
This element indicates that the property may appear in the DAV:orderby
element<!ELEMENT sortable EMPTY >
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5.19.7 The DAV:casesensitive Property Description
This element only applies to properties whose data type is "string" 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
The DAV:operators element describes every optional operator supported
in a query. (Mandatory operators are not listed since they are
mandatory and permit no variation in syntax.). All optional operators
that are supported MUST be listed in the DAV:operators element. The
listing for an operator consists of the operator (as an empty
element), followed by one element for each operand. The operand MUST
be either DAV:operand _property or DAV:operand _literal, which
indicate that the operand in the corresponding position is a property
or a literal value, respectively. If an operator is polymorphic
(allows more than one operand syntax) then each permitted syntax MUST
be listed separately.
<D:propdesc><D:like/><D:operand_property/><D:operand_literal/></D:propdesc>
5.19.9 Example of Query Schema for DAV:basicsearch
<D:basicsearchschema xmlns:D="DAV:"
xmlns:t="urn:uuid:C2F41010-65B3-11d1-A29F-00AA00C14882/"
xmlns:J="http://jennicam.org">
<D:properties>
<D:propdesc>
<D:prop><D:getcontentlength/></D:prop>
<D:datatype><t:int></D:datatype>
<D:searchable/><D:selectable/><D:sortable/>
</D:propdesc>
<D:propdesc>
<D:prop><D:getcontenttype/><D:displayname></D:prop>
<D:searchable/><D:selectable/> <D:sortable/>
</D:propdesc>
<D:propdesc>
<D:prop><J:fstop/></D:prop>
<D:selectable/>
</D:propdesc>
</D:properties>
<D:operators>
<D:opdesc>
<D:isdefined/><D:operand_property/>
</D:opdesc>
<D:opdesc>
<D:like/><D:operand_property/><D:operand_literal/>
</D:opdesc>
</D:operators>
</D:basicsearchschema> This response lists four properties. The
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datatype of the last three properties is not given, so it defaults to
string. All are selectable, and the first three may be searched. All
but the last may be used in a sort. Of the optional DAV operators,
DAV:isdefined and DAV:like are supported.
Note: The schema discovery defined here does not provide for discovery
of supported values of the DAV:casesensitive attribute. This may
require that the reply also list the mandatory operators.
6 Internationalization Considerations
Clients have the opportunity to tag properties when they are stored in
a language. The server SHOULD read this language-tagging by examining
the xml:lang attribute on any properties stored on a resource.
The xml:lang attribute specifies a nationalized collation sequence
when properties are compared.
Comparisons when this attribute differs have undefined order.
7 Security Considerations
This section is provided to detail issues concerning security
implications of which DASL applications need to be aware. All of the
security considerations of HTTP/1.1 also apply to DASL. In addition,
this section will include security risks inherent in searching and
retrieval of resource properties and content.
A query must not allow one to retrieve information about values or
existence of properties that one could not obtain via PROPFIND. (e.g.
by use in DAV:orderby , or in expressions on properties.)
A server should prepare for denial of service attacks. For example a
client may issue a query for which the result set is expensive to
calculate or transmit because many resources match or must be
evaluated. 7.1 Implications of XML External Entities
XML supports a facility known as "external entities", defined in
section 4.2.2 of [REC-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 [REC-XML]. However, [REC-XML] does state that an XML processor may,
at its discretion, include the external XML entity.
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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 [RFC2376]. Therefore,
implementers must be aware that external XML entities should be
treated as untrustworthy.
There is also the scalability risk that would accompany a widely
deployed application which made use of external XML entities. In this
situation, it is possible that there would be significant numbers of
requests for one external XML entity, potentially overloading any
server which fields requests for the resource containing the external
XML entity.
8 Scalability
Query grammars are identified by URIs. Applications SHOULD not attempt
to retrieve these URIs even if they appear to be retrievable (for
example, those that begin with "http://")
9 Authentication
Authentication mechanisms defined in WebDAV will also apply to DASL.
10 IANA Considerations
This document uses the namespace defined by [WebDAV] for XML elements.
All other IANA considerations mentioned in [WebDAV] also applicable to
DASL
11 Copyright
To be supplied.
12 Intellectual Property
To be supplied.
13 References
13.1 Normative References
[DASLREQ] J. Davis, S. Reddy, J. Slein, "Requirements for DAV
Searching and Locating", Feb 24, 1999, internet-draft,
work-in-progress, draft-dasl-requirements-01.txt
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[RFC2068] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, U.C.
Irvine, DEC, MIT/LCS, January 1997.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels." RFC 2119, BCP 14. Harvard University. March,
1997.
[RFC2376] E. Whitehead, M. Murata, "XML Media Types". RFC 2376, July
1998.
[WebDAV] Y. Goland, E.J. Whitehead, A. Faizi, S.R. Carter, D. Jenson,
"HTTP Extensions for Distributed Authoring -- WebDAV", RFC 2518,
February 1999.
[XML] T. Bray, J. Paoli, C. M. Sperberg-McQueen, "Extensible Markup
Language (XML) 1.0", September 16, 1998, W3C Recommendation.
[XMLNS] T. Bray, D. Hollander, A. Layman, "Namespaces in XML",
14-January-1999, W3C Recommendation.
http://www.w3.org/TR/REC-xml-names/ .
13.2 Non-Normative References
[ANSISQL] ANSI, "Information Systems - Database Language - SQL
(includes ANSI X3.168-1989)", ANSI X3.135-1992 (R1998), 1992.
14 Author's Addresses
Saveen Reddy
Microsoft
One Microsoft Way
Redmond WA, 9085-6933
Email:saveenr@microsoft.com
Dale Lowry
Novell
1555 N. Technology Way
M/S ORM-M-314
Orem, UT 84097
Email: dlowry@novell.com
Surendra Reddy
Oracle Corporation
600 Oracle Parkway, M/S 6op3,
Redwoodshores, CA 94065
Email: skreddy@us.oracle.com
Phone:(650) 506 5441
Rick Henderson
Netscape
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Email: rickh@netscape.com
Jim Davis
CourseNet Systems
San Francisco, CA
Email: jrd3@alum.mit.edu
Alan Babich
Filenet
3565 Harbor Blvd.
Costa Mesa, CA 92626
714-966-3403
Email: ababich@filenet.com
15 APPENDICES
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 (either because the
property is not defined for the current resource, or because it is
null for the current resource), then the value of that property is
undefined for the resource under scan. DASL 1.0 has no arithmetic
division operator, but if it did, division by zero would be an
undefined arithmetic expression.
If any subpart of an arithmetic, string, or datetime subexpression is
undefined, the whole arithmetic, string, or datetime subexpression is
undefined.
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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:
UNKNOWN and UNKNOWN = UNKNOWN
UNKNOWN or UNKKNOWN = UNKNOWN
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
16 Change History
Feb 14, 1998
Initial Draft
Feb 28, 1998
Referring to DASL as an extension to HTTP/1.1 rather than DAV
Added new sections "Notational Conventions", "Protocol Model",
"Security Considerations"
Changed section 3 to "Elements of Protocol"
Added some stuff to introduction
Added "result set" terminology
Added "IANA Considerations".
Mar 9, 1998
Moved sub-headings of "Elements of Protocol" to first level and
removed "Elements of Protocol" Heading.
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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 weekĘs 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 AuthorĘs 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
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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.
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