INTERNET-DRAFT                                       Alan Babich, Filenet
draft-davis-dasl-protocol-00.html                    Jim Davis, CourseNet (ed)
                                                     Rick Henderson, Netscape
                                                     Dale Lowry, Novell
                                                     Saveen Reddy, Microsoft
						     Surendra Reddy, Oracle
                                                     

Expires Oct 20, 2000                            April 20, 2000

Status of this Memo

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

This document is an Internet draft. Internet drafts are working documents of the Internet Engineering Task Force (IETF), its areas and its working groups. Note that other groups may also distribute working information as Internet drafts.

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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

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,
and
• the DAV:basicsearch XML element and query grammar

1.2 Relationship to DAV

1.3 Terms

1.4 Notational Conventions

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

• 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

2.1 Overview

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

2.2.1 The Request-URI

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

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 >

2.4 The Successful 207 (Multistatus) Response

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.

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

2.4.1 Example: A Simple Request and Response

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>

HTTP/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>

2.5 Unsuccessful Responses

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.

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

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>
    … the query goes here …
  </D:basicsearch>
</D:searchrequest>

>> Response

HTTP/1.1 507 Insufficient Storage
Content-Type: text/xml
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

2.6.1 Indicating 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:response in the DAV:multistatus identifies a scope. To indicate that this scope is the source of the error, the server MUST include the DAV:scopeerror element.

2.6.2 Example of an Invalid Scope

HTTP/1.1 400 Bad-Request
Content-Type: text/xml   
Content-Length: xxxxx

<?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 Syntax for DAV:scopeerror

<!ELEMENT scopeerror                    EMPTY>

3. Discovery of Supported Query Grammars

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 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]

For example:

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

3.3 Example: Grammar Discovery

>> Request

OPTIONS /somefolder HTTP/1.1
Connection: Close
Host: ryu.com

HTTP/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 The DAV:basicsearch Grammar

4.1 Introduction

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.

4.2 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) >
<!ATTLIST like   casesensitive   (1|0) "1" >

<!ELEMENT contains      (#PCDATA)>

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

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

<!ELEMENT descending    EMPTY>


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

4.2.1 Example Query

<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>

4.3 DAV:select

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.

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

4.4 DAV:from

DAV:href is an arbitrary absolute URI.

If the URI is that of a collection, then: If DAV:depth is "0", the search includes only the collection itself. If it is "1", the search includes the (toplevel) members of the collection. If it is "infinity", the search includes all recursive members of the collection.

If the URI is not a collection, the meaning of the depth element is not defined. It must nevertheless be provided.

4.4.1 Invalid scopes

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>

4.5 DAV:where

4.5.1 Use of Three-Valued Logic in Queries

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

4.5.2 Handling Optional operators

4.5.3 Treatment of NULL Values

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

4.5.4 Example: Testing for Equality

<d:where>
  <d:eq>
    <d:prop> <d:getcontentlength/> </d:prop>
    <d:literal> 100 </d:literal>
  </d:eq>

</d:where>

4.5.5 Example: Relative Comparisons

<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>

4.6 DAV:orderby

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]).

4.6.1 Comparing Natural Language Strings.

The DAV:casesensitive attribute may be used to indicate case-sensitivity for comparisons.

4.6.2 Example of Sorting

<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>

4.7 Boolean Operators: DAV:and, DAV:or, and DAV:not

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.

4.8 DAV:eq

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

4.9 DAV:lt, DAV:lte, DAV:gt, DAV:gte

4.10 DAV:literal

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.

4.11 DAV:isdefined

Example:

<d:isdefined>
  <d:prop><x:someprop/></d:prop>
</d:isdefined>

4.12 DAV:like

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.

4.12.1 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 "?" 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..

4.12.2 Example of DAV:like

<D:where>
  <D:like>
    <D:prop><D:getcontenttype/></D:prop>
    <D:literal>image%</D:literal>
  </D:like>
</D:where>

4.13 DAV:contains

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.

4.13.1 Examples

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>

<D:where>
  <D:and>
    <D:contains>Peter</D:contains>
    <D:contains>Forsberg</D:contains>
  </D:and>
</D:where>

4.14 The DAV:limit XML Element

<!ELEMENT limit (nresults) >

4.15 The DAV:nresults XML Element

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

4.16 The DAV:casesensitive XML attribute

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.

4.17 The DAV:score Property

<!ELEMENT score (#PCDATA)>

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

4.18 The DAV:iscollection Property

<!ELEMENT iscollection  (#PCDATA)>

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.

4.18.1 Example of DAV:iscollection

<D:where>
  <D:eq>
    <D:prop><D:iscollection></D:prop>
    <D:literal>1<D:literal>
  </D:eq>
</D:where>

7 Internationalization Considerations

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

Comparisons when this attribute differs have undefined order.

8 Security Considerations

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.

8.1 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.

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.

9 Scalability

10 Authentication

11 IANA Considerations

12 Copyright

13 Intellectual Property

14 References

14.1 Normative References

[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/.

14.2 Non-Normative References

15 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
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

16 APPENDICES

Three-Valued Logic in DAV:basicsearch

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.

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

17 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.

Added an sentence in introduction explaining that this is a "sketch" of a protocol.

Mar 11, 1998

Added orderby, data typing, three valued logic, query schema property, and element definitions for schema for basicsearch.

April 8, 1998

- made changes based on last week’s DASL BOF.

May 8, 1998

Removed most of DAV:searcherror; converted to DAV:searchredirect

Altered DAV:basicsearch grammar to use avoid use of ANY in DTD

June 17, 1998

-Added details on Query Schema Discovery

-Shortened list of data types

June 23, 1998

moved data types before change history

rewrote the data types section
removed the casesensitive element and replace with the casesensitive attribute
added the casesensitive attribute to the DTD for all operations that might work on a string

Jul 20, 1998

A series of changes. See Author’s meeting minutes for details.

July 28, 1998

Changes as per author's meeting. QSD uses SEARCH, not PROPFIND.

Moved text around to keep concepts nearby.
Boolean literals are 1 and 0, not T and F.
contains changed to contentspassthrough.
Renamed rank to score.

July 28, 1998

Added Dale Lowry as Author

September 4, 1998

Added 422 as response when query lists unimplemented operators.

DAV:literal declares a default value for xml:space, 'preserve' (see XML spec, section 2.10)
moved to new XML namespace syntax

September 22, 1998

Changed "simplesearch" to "basicsearch"

Changed isnull to isdefined
Defined NULLness as having a 404 or 403 response
used ENTITY syntax in DTD
Added redirect

October 9, 1998

Fixed a series of typographical and formatting errors.

Modified the section of three-valued logic to use a table rather than a text description of the role of UNKNOWN in expressions.

November 2, 1998

Added the DAV:contains operator.

Removed the DAV:contentpassthrough operator.

November 18, 1998

Various author comments for submission

June 3, 1999

Cosmetic and minor editorial changes only. Fix nits reported by Jim Whitehead in email of April 26, 1999. Converted to HTML from Word 97, manually.

April 20, 2000

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