Network Working Group R J. Godoy Internet-Draft H. Minni Intended status: Experimental Universidad Nacional del Litoral Expires: August 28, 2008 February 25, 2008 A WebDAV Search Grammar for XML Properties draft-godoy-webdav-xmlsearch-02 Status of This Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 28, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document specifies xml-search, a search grammar for use with the Web Distributed Authoring and Versioning (WebDAV) SEARCH protocol. It extends the DAV:basicsearch grammar with XPath expressions that are evaluated on resources' properties whose values are XML fragments. The full expression power of XPath may exceed the requirement in simple use cases; therefore, some provisions are made in order to Godoy & Minni Expires August 28, 2008 [Page 1] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 reduce the computational cost of evaluating allowed queries. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Notational conventions . . . . . . . . . . . . . . . . . . 4 1.2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4. WXS:xml-search and the PROPFIND response . . . . . . . . . 7 2. XPath . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Static and Dynamic Contexts . . . . . . . . . . . . . . . 8 2.2. Error and warnings . . . . . . . . . . . . . . . . . . . . 10 2.2.1. Warnings . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.2. Errors (in SAP) . . . . . . . . . . . . . . . . . . . 11 2.2.3. Errors (in DEP) . . . . . . . . . . . . . . . . . . . 11 2.3. Numeric Predicates . . . . . . . . . . . . . . . . . . . . 12 3. Discovery of the Query Grammar . . . . . . . . . . . . . . . . 13 3.1. The DASL Response Header . . . . . . . . . . . . . . . . . 13 3.2. DAV:supported-query-grammar-set . . . . . . . . . . . . . 13 3.3. Discovery of the WXS:xml-search Query Schema . . . . . . . 14 4. The WXS:xml-search Grammar . . . . . . . . . . . . . . . . . . 15 4.1. Accepted Role Precondition . . . . . . . . . . . . . . . . 16 4.2. Selection . . . . . . . . . . . . . . . . . . . . . . . . 17 4.3. Query criteria . . . . . . . . . . . . . . . . . . . . . . 18 4.3.1. DAV:prop operand . . . . . . . . . . . . . . . . . . . 19 4.3.2. Literal Operands . . . . . . . . . . . . . . . . . . . 19 4.3.3. Relational operators . . . . . . . . . . . . . . . . . 19 4.3.4. The WXS:filter operator . . . . . . . . . . . . . . . 20 4.3.5. The WXS:is-well-formed operator . . . . . . . . . . . 20 4.4. Ordering . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.5. SEARCH Status Codes for responses to WXS:xml-search queries . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.6. Status Codes for Use in 'response' Elements . . . . . . . 22 4.7. Status Codes for Use in 'propstat' Elements . . . . . . . 22 4.8. Precondition and postcondition Codes . . . . . . . . . . . 22 4.8.1. WXS:property-must-be-well-formed-xml . . . . . . . . . 22 4.8.2. WXS:acceptable-role . . . . . . . . . . . . . . . . . 23 4.8.3. WXS:XPath-error . . . . . . . . . . . . . . . . . . . 23 4.8.4. DAV:search-scope-valid . . . . . . . . . . . . . . . . 23 4.8.5. WXS:known-literal-type . . . . . . . . . . . . . . . . 23 5. Query Schema for WXS:xml-search . . . . . . . . . . . . . . . 24 5.1. Property descriptions . . . . . . . . . . . . . . . . . . 24 5.2. Operator descriptions . . . . . . . . . . . . . . . . . . 25 5.2.1. WXS:opdesc-rule and WXS:operator . . . . . . . . . . . 26 5.2.2. WXS:repetition . . . . . . . . . . . . . . . . . . . . 27 5.2.3. WXS:alternative . . . . . . . . . . . . . . . . . . . 28 5.2.4. Implied operator description . . . . . . . . . . . . . 28 5.2.5. Extended operator description for DAV:typed-literal Operand . . . . . . . . . . . . . . 29 Godoy & Minni Expires August 28, 2008 [Page 2] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 5.2.6. Description of DAV:like Operator . . . . . . . . . . . 30 5.3. Supporting Optional Functions . . . . . . . . . . . . . . 30 6. XML Extensibility . . . . . . . . . . . . . . . . . . . . . . 32 7. Security Considerations . . . . . . . . . . . . . . . . . . . 33 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9.1. Normative References . . . . . . . . . . . . . . . . . . . 34 9.2. Informative References . . . . . . . . . . . . . . . . . . 36 Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . . Appendix A. Example WXS:xml-search query . . . . . . . . . . . . 39 Appendix B. Reported Issues . . . . . . . . . . . . . . . . . . . 40 B.1. Editorial Issues . . . . . . . . . . . . . . . . . . . . . 40 B.2. Technical Issues . . . . . . . . . . . . . . . . . . . . . 41 Appendix C. Change log (To be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . . . . 42 C.1. changes in draft-godoy-webdav-xmlsearch-01 . . . . . . . . 42 C.2. changes in draft-godoy-webdav-xmlsearch-02 . . . . . . . . 42 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Note Discussion about this draft should be addressed via . The latest version of this document can be accessed at . Godoy & Minni Expires August 28, 2008 [Page 3] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 1. Introduction This document specifies xml-search, an OPTIONAL search grammar for use with the Web Distributed Authoring and Versioning (WebDAV) SEARCH protocol. The search grammar defined by this document is a superset of DAV:basicsearch [I-D.reschke-webdav-search]. The intent of this document is to extend the DAV:basicsearch grammar for dealing with properties whose values are XML fragments. Since the WebDAV property namespace is flat, and resources may have at most one value for a property of a given name (Section 9.1 of [RFC4918]), XML documents allowing repeatable elements cannot be expressed as a set of independent WebDAV properties (e.g., by mapping some elements to properties), and the DAV:basicsearch schema cannot be applied to such XML content because it deals with property values as a whole. [note-intent] WXS:xml-search is proposed as a different search grammar because it defines a new element (namely WXS:filter) that modify the query semantics. Had this been an extension of DAV:basicsearch, a server would have ignored the WXS:filter elements (according to Section 17 of [RFC4918]) yielding results different from those requested by the client. [note-RFC4918-sect17] 1.1. 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]. This specification defines elements in the urn:ietf:params:xml:ns:webdav-xml-search XML namespace. (hereinafter referred to as the "WXS namespace", though the prefix binding "WXS:" is not normative). In natural language, an element like "xml-search" in this namespace is sometimes referred to as "WXS:xml-search" (without quotes). [note-namespace] In element definitions, an element name prefixed with "WXS:" refers to an element in the WXS namespace, and un-prefixed element names refers to elements in the "DAV:" namespace. The DTD fragments are normative up to extensibility rules defined in Section 6. Unless noted otherwise, ordering of declared content is not significative. Note: when an error condition is described, it is said that "the server MUST return" some indication of that error. Unless stated otherwise, if several errors occur at the same time, any of them MAY Godoy & Minni Expires August 28, 2008 [Page 4] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 be reported and any of them MAY be omitted as long as one of them is reported. 1.2. Terms This document uses the terms defined in [RFC2616], [RFC4918], [W3C.REC-xpath20-20070123], and this section. Some definitions of frequently used terms from [W3C.REC-xpath20-20070123] are informatively included here. Dynamic Context: (of an XPath expression) "the dynamic context of an expression is defined as information that is available at the time the expression is evaluated" (Section 2.1.2, [W3C.REC-xpath20-20070123]). Dynamic Evaluation Phase (DEP): "The dynamic evaluation phase is the phase during which the value of an expression is computed. It occurs after completion of the static analysis phase" (Section 2.3.3.2, [W3C.REC-xpath20-20070123]). Dynamic Error: "A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase. Numeric overflow is an example of a dynamic error" (Section 2.3.1, [W3C.REC-xpath20-20070123]). Implementation-defined: "indicates an aspect that MAY differ between implementations, but MUST be specified by the implementor for each particular implementation" (Section 1, [W3C.REC-xpath20-20070123]). Implementation-dependent: "indicates an aspect that MAY differ between implementations, is not specified by [this or any other] specification, and is not required to be specified by the implementor for any particular implementation" (Section 1, [W3C.REC-xpath20-20070123]). Role: a context within WXS:xml-search where the DAV:prop element is expected. A role is "plain" if the DAV:prop element occurs as a direct child of DAV:select, DAV:where, or DAV:order, and it is "filtered" (also referred as XPath-enabled) if the DAV:prop element occurs as a direct child of WXS:XPath. Static Analysis Phase (SAP): "The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas)" (Section 2.3.3.1, [W3C.REC-xpath20-20070123]). Static Context: (of an XPath expression) "the static context of an expression is the information that is available during static Godoy & Minni Expires August 28, 2008 [Page 5] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 analysis of the expression, prior to its evaluation" (Section 2.1.1, [W3C.REC-xpath20-20070123]). Static Error: "A static error is an error that MUST be detected during the static analysis phase. A syntax error is an example of a static error" (Section 2.3.1, [W3C.REC-xpath20-20070123]). Type Error: "A type error may be raised during the static analysis phase or the dynamic evaluation phase. During the static analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the dynamic evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs" (Section 2.3.1, [W3C.REC-xpath20-20070123]). 1.3. Overview Section 1.4 summarizes how this query grammar matches the PROPFIND response, according to the requirement imposed by Section 2.3.2 of [I-D.reschke-webdav-search]. Section 2 describes WXS:xml-search as an XPath host language, i.e., a language where XPath expressions are embedded. This section constrains some implementation-defined items from XPath. It also includes design decisions in order to reduce the computational cost of evaluating allowed queries. Section 3 describes how this grammar is advertised, according to the mechanisms for discovery of supported query grammars, defined in Section 3 of [I-D.reschke-webdav-search]. This includes the Allow and DASL headers in OPTIONS responses (Section 3.1), the DAV: supported-query-grammar-set property (Section 3.2) and Query Schema Discovery (Section 3.3 and Section 5). Section 4 describes the grammar of a WXS:xml-search query. This includes extending the specification of selection (Section 4.2) query criteria (Section 4.3) and ordering (Section 4.4) with respect to DAV:basicsearch. Additionally, some status (Section 4.5 to Section 4.7) and precondition/postcondition codes (Section 4.8) are defined. Section 5 describes the Query Schema for advertising supported features about properties (Section 5.1) and operators (Section 5.2), and optional XPath functions available in a WXS:xml-search query (Section 5.3). Section 6 describes the specified behaviour when unexpected elements Godoy & Minni Expires August 28, 2008 [Page 6] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 are found, providing a common ground for allowing clients that implement arbitrary extensions to interoperate with other implementations that does not include it. 1.4. WXS:xml-search and the PROPFIND response A WXS:xml-search response contains a subset of the elements that a PROPFIND response, listing the same properties on the same scope and with the same depth, contains. If a server supports specifying several scopes in a single query, and these scopes exist, then the WXS:xml-search response will describe a subset of the elements in several PROPFIND responses (one PROPFIND for each scope). The DAV:select element of a WXS:xml-search request defines the result record. When either DAV:allprop or DAV:prop are used, both DAV: select and PROPFIND define the same result set. Besides, a WXS:xml- search request specifying not only DAV:allprop but also DAV:prop defines the same result set as a PROPFIND specifying DAV:allprop and DAV:include does. WXS:xml-search introduce a new way for selecting properties: WXS: filter, which "filters" elements from some property value according to an XPath expression. If WXS:filter is used, the WXS:xml-search response will contain a subset of elements from the filtered property, while the PROPFIND response will contain the complete value. Queries may impose conditions about which or how many resources will be included in the response, and servers may truncate the response at their choice. Thus, a SEARCH response may not include some resources from the specified scope, while all of them have to be included when using PROPFIND. Furthermore, WXS:xml-search defines additional preconditions and postconditions codes that are not used with a PROPFIND response. 2. XPath There are several items in XPath that are implementation-defined. Some of them are defined in this section (as this protocol specifies an XPath host language) while other are left to the criteria of the implementors. * Some components of the static and dynamic contexts are constrained (Section 2.1). Godoy & Minni Expires August 28, 2008 [Page 7] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 * A way for reporting errors and warnings is specified (Section 2.2). * In some expressions, supporting numeric predicates is OPTIONAL (Section 2.3). * Implementations of this protocol MUST be based on the rules of [W3C.REC-xml11-20060816] and [W3C.REC-xml-names11-20060816], and apply them consistently. * The self, child, descendant, descendant-or-self, parent and attribute axes MUST be supported. An implementation MAY support other axes, as described in the query schema. (This requirement is aligned with the mandatory axes from [W3C.REC-xquery-20070123].) * Support for the "Static Typing Feature" and "Static Typing Extensions" (Appendix F.1 of [W3C.REC-xpath20-20070123]) is implementation-defined. 2.1. Static and Dynamic Contexts This specification defines REQUIRED values for some components of the XPath static and dynamic context. Unless specified otherwise, the constant values specified below MUST NOT be overwritten. Components not listed here are "implementation-dependent". Evaluation of an expression that relies on one or more "unassigned" components raises the static error err:XPST0001 (if the component is static) or the dynamic error err:XPDY0002 (if the component is dynamic). Definition of functions in the "Function signatures" set is given in [W3C.REC-xpath-functions-20070123]. REQUIRED static values +---------------------+---------------------------------------------+ | Component | Specified Value | +---------------------+---------------------------------------------+ | XPath 1.0 | "false". | | compatibility mode | | | | | | Statically known | All the namespace bindings in scope at the | | namespaces | WXS:XPath element where the expression | | | occurs plus ("fn:", | | | "http://www.w3.org/2005/XPath-functions") | | | unless overwritten. | | | | | Default | The default namespace of the WXS:XPath | Godoy & Minni Expires August 28, 2008 [Page 8] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 | element/type | element where the expression occurs ("none" | | namespace | if there is no default namespace). | | | | | Default function | "http://www.w3.org/2005/XPath-functions". | | namespace | | | | | | Function signatures | fn:root($arg as node()?) as node()? | | | fn:not($arg as item()*) as xs:boolean | | | fn:count ($arg as item()*) as xs:integer | | | fn:exists($arg as item()*) as xs:boolean | | | fn:empty ($arg as item()*) as xs:boolean | | | (may be overwritten). | | | | | Statically known | At least | | collations | "http://www.iana.org/assignments/collation/ | | | default" and applicable wildcard collations | | | (Sections 3.1 and 3.2 of [RFC4790]). MAY | | | be augmented with an implementation-defined | | | set of collations. | | | | | Default collation | The collation matched by | | | "http://www.iana.org/assignments/collation/ | | | default" (the actual collation is | | | implementation-defined) | | | | | Base URI | Unassigned. | | | | | Statically known | Initially unassigned. Overwriteable with | | documents | an implementation-defined value. | | | | | Statically known | Initially unassigned. Overwriteable with | | collections | an implementation-defined value. | | | | | Statically known | node()* | | default collection | | | type | | +---------------------+---------------------------------------------+ REQUIRED dynamic values +------------------+------------------------------------------------+ | Component | Specified Value | +------------------+------------------------------------------------+ | Function | Implementation-defined, MUST be consistent | | implementations | with function signatures. | | | | | Current dateTime | REQUIRED implementation-dependent value. | | | | Godoy & Minni Expires August 28, 2008 [Page 9] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 | Implicit | REQUIRED implementation-defined value. | | timezone | | | | | | Available | Initially unassigned. Overwriteable with an | | documents | implementation-defined value. | | | | | Available | Initially unassigned. Overwriteable with an | | collections | implementation-defined value. | | | | | Default | Initially unassigned. Overwriteable with an | | collection | implementation-defined value. | +------------------+------------------------------------------------+ 2.2. Error and warnings This section describes the method for reporting XPath errors and warnings. Error conditions are defined in [W3C.REC-xpath20-20070123], and warning conditions are OPTIONAL and implementation-defined. For conformance with [W3C.REC-xpath20-20070123], implementations MAY report any non-empty subset of errors. Additionally, if there is an error (other than an XPath error) that causes the request to be rejected, implementations MAY report the latter, with no mention to the XPath errors. The idref attributes of WXS:xpath-error and WXS:warning MAY be used to refer to the id attribute of the WXS:xpath element whose content raised the error or warning. The mechanism that implementations use to return additional information is implementation-defined. 2.2.1. Warnings The WXS:warning element contains at least one XML element, and MUST NOT contain text or mixed content. Children of the WXS:warning element represent warnings signaled during the analysis of the expression. The DAV:multistatus and DAV:response elements, when used in response to WXS:xml-search queries, are modified to include an OPTIONAL WXS: warning element. Warnings raised during SAP apply to the whole query and are reported within the WXS:warning element contained by DAV: multistatus. Warnings raised during DEP only apply to a particular resource and are reported within the DAV:response for that resource. Godoy & Minni Expires August 28, 2008 [Page 10] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 The WXS:xpath-error element MUST contain one or more elements describing the error. For instance, if an err:XPST0003 were raised (i.e. the XPath static error 0003: "a XPath expression is not a valid instance of the grammar") the response would be: HTTP/1.1 400 Bad Request Content-Type: text/xml; charset="utf-8" Content-Length: xxx (Note: the use of the "err:" prefix follows the convention of [W3C.REC-xpath20-20070123] but it is not normative.) 2.2.3. Errors (in DEP) An expression may be statically valid and raise an error under some dynamic conditions. Dynamic and type errors detected during DEP only invalidates the expression which raises them, when evaluated with the actual values of some resource property. A server MAY ignore errors detected in DEP if: -The error would occur within DAV:order, but that ordering criteria is not evaluated (e.g., because other orders take precedence, or because the query matches one or no resource). -The error occurs within DAV:where part, and it does not affect Godoy & Minni Expires August 28, 2008 [Page 11] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 the result. For instance, the error in (FALSE AND ERROR) may be omitted because the result would have been FALSE anyway, and the error in (TRUE OR ERROR) may be omitted because the result would have been TRUE anyway. If the error is not ignored, and the XPath expression was specified within the DAV:select part, it MAY be reported in the DAV:propstat element for the current property and resource. Otherwise, it MAY be reported in the DAV:response element for the current resource. In both cases the status code 409 (Conflict) MUST be used. Although errors in DEP depend on the value of the property, an error that is too frequent might have been caused by mistakes in the client's request. Therefore, instead of returning a sequence of DAV: response elements, all of which represent failures because of the same error, a server MAY report an error in DEP as a general failure invalidating the query itself, even if it is possible to evaluate some resources or properties. [error-DEP] When an error raised in DEP is reported as a general failure, the response will be marshaled as in Section 2.2.2, but the response status code MUST be 409 (Conflict) instead of 400 (Bad Request). For instance, if err:XPTY0004 were raised during DEP ("the dynamic type of a value does not match a required type"), the response would be: HTTP/1.1 409 Conflict Content-Type: text/xml; charset="utf-8" Content-Length: xxx the dynamic type of a value does not match a required type 2.3. Numeric Predicates "A step is a part of a path expression that generates a sequence of items and then filters the sequence by zero or more predicates" (Section 3.2.1 of [W3C.REC-xpath20-20070123]). A step expression may be either a FilterExpr or an AxisExpr. "A predicate consists of an expression, called a predicate Godoy & Minni Expires August 28, 2008 [Page 12] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others". (Section 3.2.2 of [W3C.REC-xpath20-20070123]) Support for numeric predicates and other references to the context position -e.g. by evaluating the fn:position() function- depends on the sequence where the predicate applies. Supporting numeric predicates in FilterExpr is OPTIONAL. If the step expression is an AxisStep, the requirement level depends on the specified axis. It is: * NOT RECOMMENDED for the namespace and attribute axes, because the relative order of elements within these axes is implementation- dependent. * Always REQUIRED for the parent, self, and ancestor axes. * For the child, preceding-sibling, and following-sibling axes: RECOMMENDED if the sequence order is semantically meaningful, OPTIONAL otherwise. * Always OPTIONAL for the descendant, descendant-or-self, ancestor- or-self, preceding, and following axes. [note-context-position] The way this feature is supported when it is not REQUIRED is implementation-dependent. 3. Discovery of the Query Grammar If a resource supports the SEARCH method, then the server MUST list SEARCH in the Allow header, as described in Section 3.1 of [I-D.reschke-webdav-search]. 3.1. The DASL Response Header The DASL response header indicates server support for a query grammar in the OPTIONS method. (Section 3.2 of [I-D.reschke-webdav-search]) The value of this header is a URI that indicates the type of grammar supported. Servers MUST return the following header when the OPTIONS method is invoked on any arbiter that supports the WXS:xml-search grammar: DASL: 3.2. DAV:supported-query-grammar-set The WebDAV property DAV:supported-query-grammar-set is REQUIRED for any server supporting either [RFC3253] and/or [RFC3744] and identifies the XML based query grammars that are supported by the Godoy & Minni Expires August 28, 2008 [Page 13] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 search arbiter resource (Section 3.3 of [I-D.reschke-webdav-search]). Servers implementing DAV:supported-query-grammar-set MUST report the following grammar for each arbiter resource supporting WXS:xml- search: 3.3. Discovery of the WXS:xml-search Query Schema Query Schema Discovery (QSD) is requested by means of the SEARCH method, including an entity with a DAV:query-schema-discovery root element. As specified in Section 4.1 of [I-D.reschke-webdav-search], the response body takes the form of a DAV:multistatus element (Section 13 of [RFC4918]), where DAV:response is extended to hold the returned query grammar inside a DAV:query-schema container element. If the DAV:query-schema-discovery element contains WXS:xml-search, then the response marshaling MUST be performed as described in this section and Section 5. Since the supported query grammars may depend on the scope, the WXS: xml-search element (when used for QSD) MAY contain a DAV:from element. Other content is unexpected in this context. If a request specifies several scopes, and the server supports them, the response MUST only contain those descriptions that are common to each scope. Request: SEARCH / HTTP/1.1 Host: host.example Content-Type: application/xml Content-Length: xxx Response: HTTP/1.1 207 Multistatus Content-Type: application/xml Content-Length: xxx Godoy & Minni Expires August 28, 2008 [Page 14] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 http://host.example HTTP/1.1 200 OK 4. The WXS:xml-search Grammar The elements used in WXS:xml-search conform the semantics given in [I-D.reschke-webdav-search] for the DAV:basicsearch grammar, and all the operators defined in Section 5 of [I-D.reschke-webdav-search] (i.e. %all_ops;) are valid in the context of a WXS:xml-search query. Additionally, some elements in the "DAV:" namespace are allowed to contain specific elements from the WXS:xml-search grammar. Therefore, the semantics of a DAV:basicsearch valid query is preserved when it is submitted as a WXS:xml-search query. This grammar also allows the additional element WXS:filter, as well as optional implementation-defined operators. The WXS:filter element specifies an XPath expression (rooted on a single property, i.e. the root element is the property whose name is included in the DAV:prop element). It is both a query-operator and a special construct valid within DAV:select and DAV:order elements. Godoy & Minni Expires August 28, 2008 [Page 15] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 //foo If DAV:allprop is specified, it is understood as in a PROPFIND request [RFC4918]: (i.e., properties defined in RFC 4918, at a minimum, plus dead properties MUST be returned). Hence, the set of properties selected by allprop vary from resource to resource. If the request includes not only DAV:allprop but also one or more DAV:prop elements specifying properties that are already returned per DAV:allprop, or the request includes a property twice in DAV:prop elements, then the redundant properties MUST be ignored (i.e. a single property value will be returned). This behaviour is similar to that of the DAV:include element in a PROPFIND request (but DAV: include is not defined for WXS:xml-search requests). There is no error when a property that would be returned per DAV: allprop is also specified within a WXS:filter element (since the client may not be aware of the properties that will be returned when DAV:allprop is specified). This combination MUST be addressed as follows: - Process the WXS:filter elements as usual. This result in properties contained in DAV:propstat; elements with status code 200, 4xx, or 5xx, as appropriate. - Select each property that would have been returned per DAV: allprop in a PROPFIND request and was not included within a WXS: filter element. 4.3. Query criteria The DAV:where element specifies optional query criteria. Only those resources that verify the query criteria are included in the result set. Godoy & Minni Expires August 28, 2008 [Page 18] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 4.3.1. DAV:prop operand The result of the DAV:prop operand is the value of the specified property of the resource being evaluated. If the property is a live one, the result datatype SHOULD be the actual property datatype. If the property is dead, or the server chooses to ignore the live property datatype, the result MUST be of type xs:string. Note: "A property name is a universally unique identifier that is associated with a schema that provides information about the syntax and semantics of the property" (Section 4.4 of [RFC4918]). Therefore, each property name SHOULD be permanently associated with at most one datatype. 4.3.2. Literal Operands DAV:literal and DAV:typed-literal allow literal values to be placed in an expression. Both literal are interpreted as defined in Section 5.10 and Section 5.11 of [I-D.reschke-webdav-search]. Besides, a request with a DAV:typed-literal specifying an unknown type MUST be rejected by returning a response with status code 422 (Unprocessable Entity) and precondition code WXS:known-literal-type. The xs:string type MUST NOT be unknown. 4.3.3. Relational operators The relational operators take a property and literal operand. WXS: xml-search inherits the five relational operators defined in [I-D.reschke-webdav-search]: DAV:eq, DAV:lt, DAV:gt, DAV:lte and DAV: gte. For each property and pair of values being compared: - per Section 4.2.1 of [W3C.REC-xmlschema-2-20041028] the result of DAV:eq; is always defined, then DAV:eq; MUST NOT return NULL. - all of DAV:lt, DAV:gt, DAV:lte and DAV:gte MUST be either undefined or consistently defined. If they are defined, they MUST also conform the result of DAV:eq (i.e., A == B iff A<=B and A>=B). If the property type is known and it is a complex type, the result of these operations SHOULD be undefined. [note-comparison-complex-type] (Values within such properties may be compared by means of XPath predicates.) If the property type is known and it is a simple built-in ordered type, the order relation used in the comparison SHOULD be that defined in [W3C.REC-xmlschema-2-20041028]. Godoy & Minni Expires August 28, 2008 [Page 19] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 If the property type is known and it is a simple type, an implementation-dependent order relation MAY be used. If a partial order is used, then trying to compare two values that are not comparable yields an undefined result. In any case, the collation algorithm is implementation-dependent. Other operators and operands retain the behaviours defined in [I-D.reschke-webdav-search]. 4.3.4. The WXS:filter operator When used inside a DAV:where element (or a sub-element thereof) WXS: filter evaluates as: - TRUE if (and only if) the XPath expression matches at least one element, - FALSE if (and only if) no element within the property is matched, - NULL if (and only if) the property does not exist or its value is not a well-formed XML fragment. 4.3.5. The WXS:is-well-formed operator The WXS:is-well-formed operator takes a DAV:prop operand and returns: - TRUE if (and only if) the property value is a well formed XML fragment. - FALSE if (and only if) the property value is not a well formed XML fragment. - NULL if (and only if) the property does not exist. Supporting this operator is REQUIRED for properties that are WXS: searchable, and OPTIONAL for properties that are only DAV:searchable. 4.4. Ordering DAV:orderby specifies a lexicographical order on the result set to be returned. Comparisons are applied as they occur in the DAV:orderby element, earlier comparisons being more significant (Section 5.6 of [I-D.reschke-webdav-search]). When used within WXS:xml-search, a DAV:orderby element MUST contain one or more DAV:order elements, which are allowed to contain a DAV: prop, a DAV:score, or a WXS:filter elements. When DAV:order contains a DAV:prop element, the ascending (alternatively, descending) order MUST be consistent with the comparison performed by DAV:lte (alternatively, DAV:gte): - If A<=B (alternatively, A>=B) according to DAV:lte, then A collates Godoy & Minni Expires August 28, 2008 [Page 20] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 before B. - If A<=B (alternatively, A>=B) is undefined, then the collation order is implementation-dependent. When DAV:order contains a DAV:score element, an integer comparison is performed on each DAV:score value computed for the DAV:contains operation. When DAV:order contains a WXS:filter element, result-sets will be logically partitioned in three equivalence classes, based on the evaluation of WXS:filter (as defined in Section 4.3). The equivalence classes are totally ordered (in ascending order) as: NULL < false < true. Ordering within each equivalence class (i.e. ordering among all the responses for which the WXS:filter element evaluates to the same value) is implementation-dependent. (The order specified for the item-type in the sequence returned by the xpath expression MAY be used.) 4.5. SEARCH Status Codes for responses to WXS:xml-search queries - 207 (Multistatus) The server accepted the request. The result set are returned within a DAV:multistatus element. - 400 (Bad Request) Error in SAP, or the query includes both a plain DAV:prop and a WXS:filter specifying the same property name. - 403 (Forbidden) The server rejected the request because the user has no privileges for performing queries under the specified arbiter resource. - 404 (Not found) The arbiter resource does not exist. - 409 (Conflict) Error in DEP (general failure) or invalid scope. - 422 (Unprocessable Entity) A property was specified in a role that is rejected for that property. An unknown type was specified in DAV:typed-literal. A required extension is not supported. Other status codes may be returned (redirections, client errors, server errors), with the meaning defined in [RFC2616]. The 207 status code MUST be used if and only if a result set is included in the response (an empty result set is allowed if the query does not match any resource). If the query could not be performed because of several errors, the error that is reported is implementation-dependent. If the client has no privileges for testing whether the arbiter Godoy & Minni Expires August 28, 2008 [Page 21] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 exists then 403 (Forbidden) SHOULD be used instead of 404 (Not found). If the client has no privileges for accessing the specified scope then 409 (Conflict) MUST be returned 4.6. Status Codes for Use in 'response' Elements - 204 (No Content) if the resource exists and no selection list was specified (i.e. the DAV:select element is empty). - 209 (Conflict) Error in DEP. The search was invalidated for resources identified by DAV:href elements in the response. If a selection list was specified, the response MUST NOT contain a DAV:status element, but a DAV:propstat listing the selected properties. If the client has no privileges for testing whether a resource exists, that resource MUST be silently omitted from the response. 5xx status codes MAY be used if an error occurs when accessing the resource. 4.7. Status Codes for Use in 'propstat' Elements - 200 (OK) for each selected property, if the property exists. - 403 (Forbidden) if the client has no privileges for accessing the selected property. - 404 (Not Found) for each property selected through DAV:allprop, DAV:prop or WXS:filter if the property does not exist (OPTIONAL). - 409 (Conflict) if a property specified in a selection WXS:filter element does not contains well-formed XML. The associated postcondition MUST be WXS:property-must-be-well-formed-xml. If the client has no privileges for testing whether the property exists, the server SHOULD either omit the property or return a 404 (Not found) status code (instead of 403). 5xx status codes MAY be used if an error occurs when accessing the property value. 4.8. Precondition and postcondition Codes 4.8.1. WXS:property-must-be-well-formed-xml Type: postcondition Use with: /multistatus/response/propstat/error, 409 Conflict Purpose: the actual property value does not contain a well-formed XML Godoy & Minni Expires August 28, 2008 [Page 22] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 fragment, and the property was specified in a WXS:filter element. 4.8.2. WXS:acceptable-role Type: precondition Use with: /error, 422 Unprocessable Entity Purpose: the WXS:xml-search request includes a property for a role where it is not acceptable. 4.8.3. WXS:XPath-error Type: precondition/postcondition Use with: /error, 400 Bad Request (precondition) /error, 409 Conflict (precondition) /multistatus/response/error, 409 Conflict (postcondition) /multistatus/response/propstat/error, 409 Conflict (postcondition) Purpose: The query includes an XPath expression that raises an error. (see Section 2.2.) 4.8.4. DAV:search-scope-valid Type: precondition Use with: /error, 409 Conflict Defined in [I-D.reschke-webdav-search] 4.8.5. WXS:known-literal-type Type: precondition Use with: /error, 422 Unprocessable Entity Purpose: The query includes a DAV:typed-literal that specifies an unknown data-type. The data-type name is included into the element Godoy & Minni Expires August 28, 2008 [Page 23] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 content. 5. Query Schema for WXS:xml-search The query schema provides information about the set of available properties and implemented operators. The query schema is marshaled within a WXS:xml-search-schema element. This element contains an unordered set of property descriptions (DAV: propdesc), operator description rules (WXS:opdesc-rule) and supported optional functions (WXS:function-set). 5.1. Property descriptions The semantics of DAV:propdesc, when used within a WXS:xml-search- schema is extended for describing whether a property may be used as root element of an XPath expression within a WXS:filter element. Since WXS:filter may appear in three different places (the record-set definition, the query criteria and the ordering criteria), the server may allow or disallow it on a separate basis. If WXS:selectable, WXS:searchable or WXS:sortable is present, then the server MUST allow this property to be used within a WXS:filter element in the applicable context (role) Properties that are WXS:selectable or WXS:searchable are also DAV: selectable or DAV:searchable respectively. For instance, if a property may be selected through an XPath expression then it is plainly selectable, and if a property may be used within a WXS:filter query criterion then it may be used as an operand of DAV:is-defined, DAV:is-well-formed. Properties that are WXS:sortable are not DAV:sortable, because comparison of complex types is undefined. Properties MUST NOT be DAV:sortable and WXS:sortable at the same time. The server MUST allow described properties to be used in the role for which they were advertised. This hint does not assert whether the property is defined on every resource in the scope, and does not assert whether the property value is well-formed XML. There SHOULD be one description for DAV:any-other-property. There MUST NOT be more than one description for each property, and one description for DAV:any-other-property. The "name" attribute of the WXS:axis element specifies the name of an optional axis, and the WXS:function-set element (Section 5.3) specifies optional functions, which the server supports for the property being described. 5.2. Operator descriptions Operators are described in a way that borrows some elements from ABNF [RFC4234] (namely repetitions and alternatives). This approach allows a flexible and compact description of operators. [note-opdesc] 5.2.1. WXS:opdesc-rule and WXS:operator WXS:operator references the name of an operator. Several operators may be defined by the same WXS:opdesc-rule, and several WXS:opdesc- rule may define incremental alternatives (that is, an initial rule may match one or more alternatives, with later rule definitions adding to the set of alternatives, as in the ABNF construction Rule1 =/ Rule2 defined in section 3.3 of [RFC4234]). For instance, is equivalent to Godoy & Minni Expires August 28, 2008 [Page 26] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Mandatory operators SHOULD be omitted from the actual schema returned by a server (since their grammar is implied). If an operator is defined or enhanced by an extension of this protocol, the server MUST return rules (i.e. one or more WXS:opdesc-rule elements) for them. If the enhanced operator is a mandatory one, then the alternative rule applies. Hence, if the response includes it means that the DAV:eq operator accepts a pair of (property, foo: bar) operands, as well as it accepts the above-defined (property, literal) and (property, typed-literal) alternatives (from the implicit grammar). The order in which operands are described is significant, because the ordering of operands within an expression is significant. 5.2.2. WXS:repetition The semantics of element WXS:repetition is similar to the ABNF Variable Repetition (e.g: *Rule) defined in Section 3.6 of [RFC4234]. The optional attributes "atleast" and "atmost" indicates minimum and maximum allowed occurrences of the described content. Default values are atleast="0" and atmost="infinity" so that allows any number of occurrences, including zero; requires at least one, with no upper limit; allows exactly 3 and allows one or two. 5.2.3. WXS:alternative The semantics of element WXS:alternative is similar to the ABNF Alternatives (e.g: Rule1 / Rule2) defined in Section 3.2 of [RFC4234]. For instance, will accept either an operand- typed-literal or an operand-literal but not both. 5.2.4. Implied operator description The following query schema describes the operators specified in this document, as well as the operators from [I-D.reschke-webdav-search], as they would be reported in a QSD response. This description is implied, i.e. servers SHOULD NOT include it in the response because these operators with these signatures are mandatory. Godoy & Minni Expires August 28, 2008 [Page 28] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 The DAV:is-collection operator is supported because WXS:xml-search extends DAV:basicsearch grammar. It can be expressed by using WXS: filter as: /collection Tests for other resource types, as well as test for no resource type may be expressed by the WXS:filter operator (provided that DAV: resourcetype is WXS:searchable). For instance, testing whether a resource has no resource type may be expressed as: count(/*)==0 5.2.5. Extended operator description for DAV:typed-literal Operand The DAV:eq, DAV:gt, DAV:lt, DAV:lte, and DAV:gte operators MAY accept a DAV:typed-literal operand, instead of DAV:literal. This alternative is not implied (i.e. if supported, it MUST be included in the QSD response). If DAV:typed-literal were supported (as defined Godoy & Minni Expires August 28, 2008 [Page 29] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 in [I-D.reschke-webdav-search]), the QSD response would include the following rule: 5.2.6. Description of DAV:like Operator If the DAV:like operator is supported (as described in Section 5.2.2 of [I-D.reschke-webdav-search], the following rule MUST be included in the QSD: 5.3. Supporting Optional Functions Optional XPath functions supported by the server are described by means of one or more WXS:function-set elements. The WXS:function-set element may occur: - As a child of WXS:xml-search-schema (with the "id" attribute setted) defining a set of functions (WXS:function elements) that may be referred from several properties. - As a child of DAV:propdesc, with the "id" and "idref" attributes implied, defining a set of functions (WXS:function elements) that is specific for the property being described. - As a child of DAV:propdesc, with the "idref" attribute pointing to a "global" WXS:xml-search-schema element. > Each WXS:function element contains zero or more WXS:function-param elements, and zero or one WXS:function-result element, describing the data type of function's parameters and result. The "name" attribute of WXS:function represents the name of the function being described. The "type" attribute of WXS:function-param and WXS:function-result specifies the data type of one function parameter, or the data type of the function result, respectively. The "cardinality" attribute is used for specifying the cardinality of the sequence accepted as parameter or returned as a result. Its allowed values are "?" (zero or one), "*" (zero or more) and "+" (one or more), as specified in Section 1.4 of [W3C.REC-xpath-functions-20070123]. The "repeatable" attribute is used for specifying whether a parameter may be specified several times. It allows the values "true" and "false", defaulting to "false" when not present. (Note: cardinality="*" states that the actual parameter value may be a sequence containing several instances of the specified type, thus it is different from repeatable="true".) Function name prefixes and type name prefixes are interpreted according to the namespaces in scope. For this purpose, the item type, the node types -e.g. node, element- [W3C.REC-xpath-datamodel-20070123] and the pseudo-type "numeric" (a shorthand for xs:integer, xs:decimal, xs:float and xs:double, defined in Section 1.4 of [W3C.REC-xpath-functions-20070123]) are unprefixed, and overrides any homonym name in the current default namespace. Godoy & Minni Expires August 28, 2008 [Page 31] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 For instance, the following function-set describes: the two- parameters version of fn:starts-with, the fn:concat function, and the fn:trace function (defined in Section 4, 7.4.1 and 7.5.2 of [W3C.REC-xpath-functions-20070123], respectively). 6. XML Extensibility The extensibility mechanism from Section 17 of [RFC4918] (i.e., to process received XML documents as if unexpected elements and attributes, and all children of unrecognized elements, were not present) may be inappropriate when dealing with queries because they would not be evaluated as specified by the client (e.g. the query criteria may be loosen or the result record or may be incomplete). The omission of unexpected content might not be realized by the client. The QSD response is the preferred method for advertising enhanced capabilities for xml-search queries. Thus clients could assert whether an extension is implemented by looking in the QSD beforehand. Any extension of this grammar that modifies the query semantics (as long as for yielding useless results if the extension were ignored) SHOULD univocally identify itself by including one or more elements in the QSD response. If the extension defines several conformance Godoy & Minni Expires August 28, 2008 [Page 32] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 degrees, it should be clear from the QSD response which part of the extension is actually implemented. When an unexpected or unknown element is present in the request, the server MUST: - Ignore it (and its descendants), if the element is not a descendant of DAV:where). The request is then processed as if the element were not there. - Fail with status code 422 (Unprocessable Entity) and precondition code WXS:unexpected-operator, if the element is a descendant of DAV:where). The server MUST ignore all unexpected or unknown attributes which occurs within expected elements. 7. Security Considerations The security considerations of WebDAV SEARCH [I-D.reschke-webdav-search], and WebDAV [RFC4918], as well as those of HTTP/1.1 [RFC2616] and XML [RFC3023] are applicable to the WebDAV extension described in this document. The risk of denial of service attacks is greater than in the DAV: basicsearch case, because evaluating some XPath expressions may be computationally expensive. Implementors must be aware that many valid (and required, even after subsetting optional XPath features) expressions are computationally expensive to evaluate. Implementations should deal with these expressions as a possible denial of service attack (DOS), which may be committed either by intention or by a good faith client submitting an overwhelming query. Some examples of this queries include: visiting repeatedly the parent and child axes, visiting several nodes with no apparent purpose (e.g. a predicate that is evaluated on some other node, unrelated to the focus), and requesting a result-set with redundant information (e.g. nodes and information derived from those nodes by applying some function). There are no universally valid rules for determining whether an expression is part of a DOS attack. Indeed, a server may accept an expression that is deemed to be useful by the server implementors or administrators, while other may reject it because of security concerns. It may also accept or reject an expression because of other variables, such as credentials presented by the user when Godoy & Minni Expires August 28, 2008 [Page 33] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 authenticating (i.e. some users may be allowed to perform certain kind of queries that would have been considered DOS if submitted by other user). For protecting from false negatives when detecting DOS, servers should timeout when queries take too much time before completion. 8. IANA Considerations This document defines XML elements in an XML namespace described by a URN conforming the registry mechanism described in [RFC3688]. The following URI assignment is requested URI: urn:ietf:params:xml:ns:webdav-xml-search Registrant Contact: See the "Author's Address" section of this document. XML: None. Namespace URIs do not represent an XML specification. Reference: The last version of this document. 9. References 9.1. Normative References [I-D.reschke-webdav-search] Reschke, J., "Web Distributed Authoring and Versioning (WebDAV) SEARCH", draft-reschke-webdav-search-15 (work in progress), February 2008. [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. Godoy & Minni Expires August 28, 2008 [Page 34] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 [RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, "Versioning Extensions to WebDAV (Web Distributed Authoring and Ve rsioning)", RFC 3253, March 2002. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol", RFC 3744, May 2004. [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet Application Protocol Collation Registry", RFC 4790, March 2007. [RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)", RFC 4918, June 2007. [W3C.REC-xml-names11-20060816] Hollander, D., Layman, A., Tobin, R., and T. Bray, "Namespaces in XML 1.1 (Second Edition)", World Wide Web Consortium Recommendatio n REC-xml-names11-20060816, August 2006, . [W3C.REC-xml11-20060816] Maler, E., Sperberg-McQueen, C., Cowan, J., Paoli, J., Bray, T., and F. Yergeau, "Extensible Markup Language (XML) 1.1 (Second Edition)", World Wide Web Consortium Recommendation REC- xml11-20060816, August 2006, . [W3C.REC-xmlschema-2-20041028] Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second Godoy & Minni Expires August 28, 2008 [Page 35] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Edition", World Wide Web Consortium Recommendation REC- xmlschema-2-20041028, October 2004, . [W3C.REC-xpath-datamodel-20070123] Fernandez, M., Malhotra, A., Nagy, M., Walsh, N., and J. Marsh, "XQuery 1.0 and XPath 2.0 Data Model (XDM)", World Wide Web Consortium Recommendation REC- xpath-datamodel-20070123, January 2007, . [W3C.REC-xpath-functions-20070123] Walsh, N., Malhotra, A., and J. Melton, "XQuery 1.0 and XPath 2.0 Functions and Operators", World Wide Web Consortium Recommendatio n REC-xpath-functions-20070123, January 2007, . [W3C.REC-xpath20-20070123] Berglund, A., Boag, S., Chamberlin, D., Kay, M., Robie, J., Fernandez, M., and J. Simeon, "XML Path Language (XPath) 2.0", World Wide Web Consortium Recomme ndation REC-xpath20-20070123, January 2007, . 9.2. Informative References [RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [W3C.REC-xquery-20070123] Boag, S., Robie, J., Chamberlin, D., Fernandez, M., Florescu, D., and J. Simeon, "XQuery 1.0: An XML Query Language", World Wide Web Consortium Recommendation REC -xquery-20070123, January 2007, < Godoy & Minni Expires August 28, 2008 [Page 36] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 http://www.w3.org/TR/2007/ REC-xquery-20070123>. Editorial Comments [error-DEP] Besides, handling dynamic errors on a separate basis imposes an additional requirement, then supporting this feature is left to the criteria of implementors. [note-comparison-complex-type] This seems to be a MUST in [draft-reschke-webdav-search-14] Section 5.5.4, but is relaxed here since the property would be treated as xs:string if the type were ignored. [note-context-position] When supporting numeric predicates and context position references there is a trade-off between expressive power and implementation costs. [note-intent] The authors' motivation for writing this document is allowing metadata to be searchable when presented as a WebDAV property. Since it may be encoded as specified by a third-party schema, it should not be modified in order to conform WebDAV. [note-namespace] Since this protocol is experimental, the authors do not suggest new elements in order to not pollute the "DAV:" namespace. Thus, an experimental implementation of this protocol will not conflict with the following requirement from RFC 4918: "(...) an XML element in the "DAV:" namespace SHOULD NOT be used in the request or response body unless that XML element is explicitly defined in an IETF RFC reviewed by a WebDAV working group". [note-opdesc] The operator description is only intended for discovering whether the server implements an extension Godoy & Minni Expires August 28, 2008 [Page 37] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 operator. The DAV:operators element from [I-D.reschke-webdav-search] is not adopted here, because it cannot describe the mandatory operators. On the other hand, while XML Schemas would have sufficed for this purpose, this approach would have required WXS:xml-search clients to be in conformance to the XML Representation of Schemas, which is much more than necessary for achieving the above mentioned goal (given that the operators are not too complex). The chosen approach is compared to ABNF, in order to avoid further relation with features that are available in XML schemas but are unsupported for xml-search-schema descriptions. [note-OPTIONAL-404] The 404 status code for missing properties is OPTIONAL in order to avoid an extensive response if the client selects several properties that are seldom defined. Note this behaviour is different from the PROPFIND case, where the 404 status code is REQUIRED for missing properties (Section 9.1 of [RFC 4918], page 35). [note-RFC4918-sect17] RFC4918: "(...) servers MUST process received XML documents as if unexpected elements and attributes (and all children of unrecognized elements) were not there" [note-select-prop-filter] If the property value is not well- formed XML specifying both DAV:prop and WXS:filter is ambiguous because a 409 (Conflict) status code must be returned per WXS:filter and the complete property value must be returned per DAV:prop. On the other hand, if the property value were well-formed XML, one of those elements would have to be ignored. Appendix A. Example WXS:xml-search query Godoy & Minni Expires August 28, 2008 [Page 38] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 This example shows a request/response exchange for selecting the DAV: getcontentlength property and the and first elements of the property, from resources that are directly contained in the http://host.example.com/ collection, such that the title (as described by an M:title element within the M:metadata property) starts with letter "S". The first results will have at least one M:author element present. The response describes two resources: - foo.pdf, with DAV:getcontentlength = 65536, author = "John Doe" and title = "Sample Title" - bar.txt, with DAV:getcontentlength = 1024, title = "Sample Anonymous Resource" and no author. Request: SEARCH / HTTP/1.1 Host: host.example.com Content-Type: application/xml Content-Length: xxx http://host.example.com/ 1 starts-with(/M:title,'S') Godoy & Minni Expires August 28, 2008 [Page 39] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 /M:author Response: HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset="utf-8" Content-Length: xxx http://host.example.com/foo.pdf 65536 John Doe Sample title HTTP/1.1 200 OK http://host.example.com/bar.txt 1024 Sample Anonymous Resource HTTP/1.1 200 OK Appendix B. Reported Issues B.1. Editorial Issues Godoy & Minni Expires August 28, 2008 [Page 40] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Issue #E1, reported by Michael Kay on 2008-01-21. http://lists.w3.org/Archives/Public/www-xpath-comments/2008JanMar/ 0001.html, item (a). http://lists.w3.org/Archives/Public/public-qt-comments/2008Jan/ 0096.html, item (a). Reference to XPath 2.0 Proposed Recommendation of 2006-11-21 should be modified to refer Recommendation of 2007-01-23 2007. Suggest avoid referring to a specifically dated version, so that readers are referred to the latest edition at any given time, which may incorporate errata. Resolution: Refer XPath 2.0 Recommendation of 2007-01-23 (in turn, it already suggests readers to check the latest version and errata). Revisit this issue later with the RFC editor. Issue #E2, reported by Michael Kay on 2008-01-21. http://lists.w3.org/Archives/Public/www-xpath-comments/2008JanMar/ 0001.html, item (c). http://lists.w3.org/Archives/Public/public-qt-comments/2008Jan/ 0096.html, item (c). Since the namespace prefix "xs" is often used to refer to the XML Schema namespace, it might be clearer to readers if a prefix other than "XS" is used (perhaps "WXS"?). Resolution: replace XS prefix with WXS. B.2. Technical Issues Issue #T1, reported by Michael Kay on 2008-01-21. http://lists.w3.org/Archives/Public/www-xpath-comments/2008JanMar/ 0001.html, item (e). http://lists.w3.org/Archives/Public/public-qt-comments/2008Jan/ 0096.html, item (e). Suggest requiring the same subset of axes as XQuery chose. Resolution: include descendant, descendant-or-self and parent as REQUIRED axes (thus aligning with XQuery required axis). The namespace axis is deprecated in XQuery, such deprecation is not inherited by xmlsearch but the namespace axis is made OPTIONAL. Issue #T2, reported by Michael Kay on 2008-01-21. http://lists.w3.org/Archives/Public/www-xpath-comments/2008JanMar/ 0001.html, item (f). The minimum set of functions that an implementation must supply is defined as being empty (no functions). There are some functions such as not() and count() that would be absolutely indispensable. Resolution: Include fn:not(item,item,...), fn:count(item,item,...), fn:exists(item,item,...), fn:empty(item,item,...), fn:root(node). fn: root(node) is supported because of the expansion for "/" and "//". The default function namespace is set to "fn". The QSD is extended for describing other functions that MAY be optionally supported. Godoy & Minni Expires August 28, 2008 [Page 41] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Appendix C. Change log (To be removed by RFC Editor before publication) C.1. changes in draft-godoy-webdav-xmlsearch-01 - Include appendix B (reported issues) and C (change log). - Removed typo about "DAV:xsl-search-schema", which does not exist. - New issues in this version: #E1, #E2, #T1, #T2. - Issues addressed in this version: #E1, #E2, #T1, #T2 - Some Security Considerations. - Minor editorial changes. C.2. changes in draft-godoy-webdav-xmlsearch-02 - Minor editorial changes. - Updated reference to draft-reschke-webdav-search-15. - Added allow-pcdata attribute in WXS:opdesc-rule, and modified section about Literal Operands, per issues addressed in draft-reschke-webdav-search-15 (discussion in http://lists.w3.org/ Archives/Public/www-webdav-dasl/2008JanMar/0022.html). - Simplified the extension mechanism, because it was too complex to be practical. Renamed precondition WXS:unexpected-content as WXS: unexpected-operator. Index A Attribute allow-pcdata (WXS:opdesc-rule) 25 atleast (WXS:repetition) 25 atmost (WXS:repetition) 25 attrname (WXS:unexpected-content element) 33 cardinality (WXS:function-param) 30 cardinality (WXS:function-result) 30 id (WXS:function-set) 30 id (WXS:xpath) 15 idref (WXS:function-set) 30 idref (WXS:warning) 10 idref (WXS:xpath-error) 11 name (WXS:axis) 24 name (WXS:function) 30 Godoy & Minni Expires August 28, 2008 [Page 42] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 name (WXS:operator) 25 namespace (WXS:operator) 25 repeatable (WXS:function-param) 30 type (WXS:function-param) 30 type (WXS:function-result) 30 D Dynamic Context 5 Dynamic Error 5 Dynamic Evaluation Phase (DEP) 5 E Element DAV:and 15 DAV:multistatus 11 DAV:not 15 DAV:or 15 DAV:order 15 DAV:propdesc 24 DAV:response 11 DAV:search-scope-valid 23 DAV:select 15 DAV:where 15 WXS:acceptable-role 23 WXS:alternative 25 WXS:axis 24 WXS:filter 15 WXS:function 30 WXS:function-param 30 WXS:function-result 30 WXS:function-set 30 WXS:is-well-formed 15 WXS:known-literal-type 23 WXS:opdesc-rule 25 WXS:operand-nested-op 25 WXS:operand-XPath 25 WXS:operator 25 WXS:property-must-be-well-formed-xml 22 WXS:repetition 25 WXS:searchable 24 WXS:selectable 24 WXS:sortable 24 WXS:unexpected-content 33 WXS:warning 10 WXS:xml-search 15 WXS:xml-search-schema 24 WXS:XPath 15 WXS:XPath-error 23 Godoy & Minni Expires August 28, 2008 [Page 43] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 WXS:xpath-error 11 Example Bad Request, DAV:select 18 DASL Response Header 13 DAV:supported-query-grammar-set 14 Description of DAV:like Operator 30 Extended operator description for DAV:typed-literal operand 30 Implied operator description 28 QSD request 14 QSD response 14 WXS:function-set 32 WXS:opdesc-rule 26-27 WXS:XPath-error (in DEP) 12 WXS:XPath-error (in SAP) 11 xml-search request 39 xml-search response 40 I Implementation-defined 5 Implementation-dependent 5 R Role 5 S Static Analysis Phase (SAP) 5 Static Context 5 Static Error 6 T Type Error 6 Authors' Addresses Roberto Javier Godoy UNL - Facultad de Ingenieria y Ciencias Hidricas Ciudad Universitaria, Ruta Nac. 168 S3001XAI Paraje "El Pozo" Argentina EMail: rjgodoy@fich.unl.edu.ar URI: http://purl.oclc.org/NET/rjgodoy Hugo Minni UNL - Facultad de Ingenieria y Ciencias Hidricas Ciudad Universitaria, Ruta Nac. 168 S3001XAI Paraje "El Pozo" Godoy & Minni Expires August 28, 2008 [Page 44] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Argentina EMail: hminni@fich.unl.edu.ar Godoy & Minni Expires August 28, 2008 [Page 45] Internet-Draft WebDAV Search Grammar for XML Properties February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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