The XML specification [Extensible Markup Language (XML) 1.0 (Fifth Edition)] defines an XML processor as "a
software module. . .used to read XML documents and provide access to their
content and structure. . .on behalf of another module, called the application."
XML applications are often defined by building on top of the [XML Information Set (Second Edition)] or other similar XML data models such as [XML Path Language (XPath) Version 1.0] or [XQuery 1.0 and XPath 2.0 Data Model (XDM)], understood as the output of an XML processor. Such definitions have suffered to some extent from an uncertainty inherent in using that kind of foundation, in that the mapping XML processors perform from XML documents to data model is not rigid. Some of this stems from the XML specification itself, which leaves open the possiblity of reading and interpreting external entities, or not. Some stems from the growth of the XML family of specifications: if the input document includes uses of XInclude, for instance.
This specification addresses this issue by defining several XML processor
profiles, each of which fully determines a data model for any given XML
document. It is intended as a resource for other specifications, which can by
a single normative reference establish precisely what input processing they require.
The profiles defined here are appropriate for processing both XML 1.0 [Extensible Markup Language (XML) 1.0 (Fifth Edition)] and XML 1.1 [Extensible Markup Language (XML) 1.1 (Second Edition)] documents. References to XML or XML Namespaces below should be understood as references to 1.0 or 1.1 as required by the relevant document or application.
[Definition: The key words
must, must not, required,
shall, shall not, should,
should not, recommended, may,
and optional in this specification are to be interpreted
as described in [RFC 2119].]
The term base URI is used in this specification as it is defined in [RFC 3986].
Data models constructed in conformance with one of the profiles defined above will
be guaranteed to share certain properties. The following sub-sections describe
this in terms of invariants with respect to the information available in the
data model.
Any two data models which are both constructed in conformance with the
same profile from a given namespace-well-formed XML
document will have
exactly the same information with repect to the following information items and
properties (per [XML Information Set (Second Edition)]):
- The Document Information Item
[document element],
[base URI],
[character encoding scheme],
[standalone],
[version],
[all declarations processed]
- Element Information Items
[namespace name],
[local name],
[prefix],
[children],
[attributes],
[namespace attributes],
[in-scope namespaces],
[base URI],
[parent]
- Attribute Information Items
[namespace name],
[local name],
[prefix],
[normalized value],
[specified],
[attribute type],
[references],
[owner element]
- Processing Instruction Information Items
[target],
[content],
[base URI],
[notation],
[parent]
- Unexpanded Entity Reference Information Items
[name],
[system identifier],
[public identifier],
[declaration base URI],
[parent]—This type of information item will not occur at all if using 2.3 The modest XML processor profile or
2.4 The recommended XML processor profile profiles, or if standalone="yes"
- Character Information Items
[character code],
[parent]
- Comment Information Items
[content],
[parent]
- Namespace Information Items
[prefix],
[namespace name]
When two data models are constructed in conformance with the
two different profiles from a given namespace-well-formed XML
document, the information contained therein will in some cases (depending on
the specifics of the document in question) differ with repect to the following information items and
properties (per [XML Information Set (Second Edition)]) (leaving aside the items and
properties identified as implementation-defined above):
- Element Information Items
Entirely, in that where a basic processor reports an Unexpanded Entity
Reference, richer ones will report the entity expansion, which may be or
include entire elements.
- Attribute Information Items
Entirely, for the same reason, or, just with respect to [normalized value],
[specified],
[attribute type] and
[references] where a basic processor has not processed the relevant
declaration, but a richer one has.
- Processing Instruction Information Items
Entirely, per the Element case above
- Unexpanded Entity Reference Information Items
Entirely, in the opposite sense to the Element case above
- Character Information Items
Entirely, per the Element case above
- Comment Information Items
Entirely, per the Element case above
- Namespace Information Items
Entirely, per the Element case above
And all the differences listed in the next section.