XML News from Wednesday, February 4, 2009

The W3C XML Schema Working Group has posted possibly the third last call working drafts of XML Schema 1.1 Part 1: Structures and XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. According to the structures draft,

The major revisions since the previous public working draft include the following:

• Attribute declarations can now be marked {inheritable} (see Inherited Attributes (§3.3.5.6)) and the values of inherited attributes are accessible in the XDM data model instance constructed for checking assertions (see Assertions (§3.13)) and for conditional type assignment (see Type Alternatives (§3.12)).
  Among other consequences, this allows conditional type assignment and assertions to be sensitive to the inherited value of the xml:lang attribute and thus to the language of the element's contents. This change was introduced to resolve issue 5003 Applicability of <alternative> element to xml:lang, raised by the W3C Internationalization Core Working Group.
• Three priority feedback requests have been added in this draft (and those in previous drafts have for the most part been retained). They concern:

  • content-model subsumption involving all-groups (see issue 5293 Subsumption)
  • detection of certain schema errors at instance-validation time (see issue 5293 Subsumption).
  • the interaction of block and substitution groups (see issue 6382 Substitution group and "block").
• The <override> facility has been revised to make the new declarations and definitions in the <override> element override matching declarations and definitions not only in the schema document directly pointed to by the schemaLocation attribute, but also in other schema documents referred to using <include> or <override> in that schema document.
  This allows the use of <override> even in cases where the declarations and definitions to be overridden are spread widely across a tightly interconnected set of schema documents, and thus makes it more widely useful.
• The discussion of <include> and <override> has been revised to eliminate an ambiguity in earlier versions of this spec regarding the meaning of cyclic dependencies formed by use of <include> and <override>: such cyclic dependencies are now clearly allowed and have a well defined meaning.
• Schema processors are now explicitly recommended to provide a user option to control whether the processor attempts to dereference schema locations indicated in schemaLocation attributes in the instance document being validated; this resolves issue 5476 xsi:schemaLocation should be a hint, should be MAY not SHOULD.
• The semantics of attributes vc:typeAvailable and vc:typeUnavailable have been revised to make them complementary and to ensure that if two constructs in the input to conditional inclusion processing are marked vc:typeAvailable="A B C" and vc:typeUnavailable="A B C", respectively, then exactly one of the two will be chosen. This change resolves issue 5905 vc:typeAvailable and vc:typeUnavailable.
• Schema processors are now encouraged to issue warnings for unrecognized attributes in the vc namespace. Attributes may be added to that namespace in the future, so unrecognized attributes are not errors, but until that time, the presence of unrecognized attributes is likely to indicate a problem in the input. This change resolves issue 5904 Unknown attributes in vc namespace.
• The constraints on the XML representation of schemas have been reformulated to allow them to be checked on schema documents in isolation, rather than requiring knowledge of the rest of the schema into which they will be embedded. The consequence is that some errors are caught not in the XML representation constraints but by having the XML mapping rules generate faulty components so that the error can be detected at the component level. These changes resolve issue 6235 Restriction from xs:anySimpleType.
• The formal grammar for the XPath expressions used in conditional type assignment has been revised to allow both cast expressions and constructor functions, and to resolve a formal ambiguity in the earlier versions of the grammar; these changes resolve issue 5907 Problem with BNF for type alternatives.
• The <schema> element is now declared with open content in the schema for schema documents. This change addressess issue 5930 defaultOpenContent in the S4SD.
• The setting blockDefault="http://www.w3.org/TR/2009/WD-xmlschema11-1-20090130/#all" has been removed from the schema for schema documents; this change resolves issue 6120 Reconsider blockDefault=http://www.w3.org/TR/2009/WD-xmlschema11-1-20090130/#all.
• Skip wildcards are now excluded from the Element Declarations Consistent (§3.8.6.3) constraint, and that constraint now also takes open content into account; these changes resolve issue 5940 Element Declarations Consistent.
• Annotations given in the XML form of identity-constraint declarations with ref attributes are now retained in the ·post-schema-validation infoset· form of the containing element declaration. This change resolves issue 6144 annotation on IDC with a 'ref' attribute is lost.
• All wildcard unions are now expressible, and wildcard union is used to combine multiple attribute wildcards, rather than wildcard intersection; this change resolves issue 6163 3.10.6.3 Attribute Wildcard Union .
• Namespace fixup is now explicitly required in some places where it is needed but was not mentioned before; these changes resolve issue 6445 Namespace fixup and default namespace and issue 6465 Namespace fixup and inherited attributes.
• The term "context-determined-declaration" has been replaced with the term ·locally declared type·; this resolves issue 4690 Editorial: 'context-determined declarations' needs more work.
• The namespace prefixes used to refer to well known namespaces have been changed and are now more consistent; this resolves issue 4316 Make sure namespace prefixes are used appropriately throughout structures.
• Numerous small changes were made in the interests of clarity, completeness, consistency, and precision, and to correct typographical errors.

In the datatypes spec,

The major changes since version 1.0 include:

• Support for XML 1.1 has been added. It is now implementation defined whether datatypes dependent on definitions in [XML] and [Namespaces in XML] use the definitions as found in version 1.1 or version 1.0 of those specifications.
• A new primitive decimal type has been defined, which retains information about the precision of the value. This type is aligned with the floating-point decimal types which will be part of the next edition of IEEE 754.
• In order to align this specification with those being prepared by the XSL and XML Query Working Groups, a new datatype named anyAtomicType which serves as the base type definition for all primitive atomic datatypes has been introduced.
• The conceptual model of the date- and time-related types has been defined more formally.
• A more formal treatment of the fundamental facets of the primitive datatypes has been adopted.
• More formal definitions of the lexical space of most types have been provided, with detailed descriptions of the mappings from lexical representation to value and from value to ·canonical representation·.
• The validation rule Datatype Valid (§4.1.4) has been recast in more declarative form. A paraphrase of the constraint in procedural terms, which corrects some errors in the previous versions of this document, has been added as a note.
• The rules governing partial implementations of infinite datatypes have been clarified.
• Various changes have been made in order to align the relevant parts of this specification more closely with other relevant specifications, including especially the corresponding sections of [XSD 1.1 Part 1: Structures].

Changes since the previous public Working Draft include the following:

• At the suggestion of the W3C OWL Working Group, a explicitTimezone facet has been added to allow date/time datatypes to be restricted by requiring or forbidding an explicit time zone offset from UTC, instead of making it optional. The dateTimeStamp datatype has been defined using this facet.
• At the suggestion of the W3C Internationalization Core Working Group, most references to "time zone" have been replaced with references to "time zone offset"; this resolves issue 4642 Terminology: zone offset versus time zone.
• The reference to the Unicode Database [Unicode Database] has been updated from version 4.1.0 to version 5.1.0, at the suggestion of the W3C Internationalization Core Working Group
• Owing to an editorial error, the previous Working Draft had an error in the definition of the lexical spaces for float and double, which excluded the literal '+INF' from their ·lexical spaces·. This error has been corrected.
• References to various other specifications have been updated.

Comments are due by February 20.