application/xml, text/xml-external-parsed-entity, or application/xml-external-parsed-entity">
]>
&abstract;
This is a Last Call W3C Working Draft for review by W3C members and other
interested parties. It is a draft document and may be updated, replaced, or
obsoleted by other documents at any time. It is inappropriate to use W3C Working
Drafts as reference material or to cite them as other than work in
progress.
Comments on this document should be sent no later than 31 July 2002 to the public mailing list
This document has been produced by the
There are patent disclosures and license commitments associated with
this working draft, which may be found on the
Even though it has not been seen before in this form, this specification
is being published as a Last Call Working Draft because it is essentially
a subset of the previous specification. This specification contains only the bare
names
and scheme mechanism features that were in the bare
names
functionality has been extended slightly to include a schema-based
ID addressing option.
We are specifically seeking input on what the XML Linking WG should recommend
as a minimum conformance level for the purposes of XPointer usage in fragment
identifiers for any resource whose Internet media type is &media-types;. Actually
specifying this level is an issue that will have to be taken up normatively
in the successor to IETF RFC 3023
A list of current W3C Recommendations and other technical documents can be
found at
recursivelyto 2(b), and added explanatory text to the note on potential failures of ID-based addressing. The WG voted to publish this draft.
&abstract;
Many types of XML-processing applications need to address into the internal
structures of XML-encoded resources using URI references, for example, the
XML Linking Language
The formal grammar for the &framework; is given using simple Extended Backus-Naur
Form (EBNF) notation, as described in the XML Recommendation
A string conforming to this specification. This specification defines the syntax and semantics of pointers.
A portion of a pointer that provides a scheme name and some pointer data that conforms to the definition of that scheme.
A specialized pointer data format that has a name and is defined in a specification.
A software component that identifies some subresource of an XML-encoded resource by applying a pointer to it. This specification defines the behavior of XPointer processors.
A software component that incorporates or uses an XPointer processor because
it needs to access XML-encoded resources by means of URI references. The occurrence
and usage of URI references, and the behavior to be applied to resources and
subresources obtained by accessing those URI references, are governed by the
definition of each application's corresponding data format (which could be
XML-based or non-XML-based). For example, HTML
A violation of the rules of this specification; results are undefined. Specifications of XPointer schemes may define their own error conditions that have different consequences from XPointer Framework errors.
The inability of an XPointer processor to identify a subresource within
an XML-encoded resource. Note that while failure of a shorthand pointer (
A list of zero or more pairs of XML Namespace-defined
This specification defines a framework; it does not currently define a minimum conformance level for XPointer processors. Thus, the information in this section defines conformance requirements only for the framework portion of any minimum conformance level.
XPointer processors normatively depend on reversing any fragment identifier
encoding and escaping done in conformance to
XPointer processors normatively depend on sufficient input about an XML resource to identify the following information items and properties, in the cases where they exist in the resource:
From the XML Information Set
Note that if the XML resource
is not a document but rather an external parsed entity, this property will
not be reported. Rather, the information set is effectively extended to report
the one or more top-level elements in the entity as ordered root element
properties
for the entity.
From the XML Schema post-schema validation information set (PSVI)
Either:
or:
Software components claiming to be XPointer processors must conform to this &framework; specification and any other specifications that, together with this specification, define the minimum conformance level for XPointer, and may conform to additional XPointer scheme specifications. XPointer processors must document the additional scheme specifications to which they conform. Specifications that depend on XPointer processing should document the schemes they require and allow.
Conforming XPointer processors must report &framework; errors to the application. Applications may terminate or recover from &framework; errors in any fashion. XPointer processors should not report failure conditions that do not result in error conditions.
This section describes the &framework; and the behavior of XPointer processors with respect to the framework.
An XPointer processor takes as input an XML-encoded resource and a fragment
identifier taken from the URI reference that was used to access the resource,
and produces as output either an identification of some subresource within
that resource based on the pointer extracted from the fragment identifier,
or one or more errors, or both. If the fragment identifier contains any characters
that have been encoded or escaped to conform to
If a string used as a pointer does not adhere to the syntax defined in this section, it is an error.
The end of a
pointer part is signaled by the right parenthesis
character
that is balanced with the left parenthesis )
character
that began the part. If either a left or a right parenthesis occurs without
being balanced by its counterpart, it must be escaped with a circumflex ((^)
character preceding it. Any literal occurrences of the circumflex must be
escaped with an additional circumflex (that is, ^^). Any other
use of a circumflex is an error.
A shorthand pointer consists of an XML-defined
If the document has an XML Schema
Return the first element information item in document order with
an
a http://www.w3.org/2001/XMLSchema"
and a ID" (having the effect of identifying
the element information item associated with an identifier that is directly
assigned the XML Schema ID type), or
a
or, if an element information item was not identified in the previous
step because the document has an XML Schema PSVI but does not expose
the
Return the first element information item in document order with
an http://www.w3.org/2001/XMLSchema"
and a ID" or a http://www.w3.org/2001/XMLSchema" and a ID";
or, if an element information item was not identified in the previous step:
Return the first element information item in document order with
an ID" and a
If no element is identified by this process, the
A shorthand pointer provides, for resources with XML-based media types,
a rough analog of HTML fragment identifier behavior. However, if
A scheme-based pointer consists of one or more pointer parts, optionally
separated by XML-defined white space (
In the case of URI references referring to any resource whose Internet media type is &media-types;, this specification reserves all scheme names for definition in additional W3C XPointer scheme specifications. However, the scheme mechanism provides a general framework for extensibility; other XML-based media types are also encouraged to use this framework in defining their own fragment identifier languages.
When multiple pointer parts are provided, an XPointer processor must evaluate them in left-to-right order. If a part being evaluated fails because the XPointer processor does not support the scheme, because the scheme data is syntactically in error according to the specification governing that scheme, or because the scheme identifies no subresource, that part is consumed and the next, if any, is evaluated. The result of the first pointer part whose evaluation succeeds is reported by the XPointer processor as the subresource identified by the pointer as a whole, and evaluation stops. If all the parts fail, it is an error. If a scheme-based pointer has an error in its construction as a whole, evaluation stops and pointer parts are not consumed.
A scheme-based pointer might contain characters that are not allowed in
a URI reference. For example, this &framework; specification allows spaces
between pointer parts, and individual XPointer scheme specifications might
allow or require other characters that are disallowed in URI references. During
creation of the pointer, it is typically not necessary to perform encoding
or escaping on disallowed characters. However, by the time a pointer is fed
as input (as a fragment identifier on a URI reference) into a URI resolver,
any such characters must have been encoded and/or escaped as defined in
Scheme specifications may define ways to bind XML Namespaces
The initial namespace binding context prior to evaluation of the first
pointer part consists of a single entry: the xml prefix bound
to the URI http:/www.w3.org/XML/1998/namespace. Pointer parts
must not attempt to redefine the xml prefix; any attempt to do
so results in no change being made to the namespace binding context.