[Bug 4367] Subsumption and assertions

http://www.w3.org/Bugs/Public/show_bug.cgi?id=4367

           Summary: Subsumption and assertions
           Product: XML Schema
           Version: 1.1 only
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Structures: XSD Part 1
        AssignedTo: cmsmcq@w3.org
        ReportedBy: mike@saxonica.com
         QAContact: www-xml-schema-comments@w3.org


The rules for Schema Component Constraint: Derivation Valid (Extension) (and
similarly, Restriction, require: 1.6 The {assertions} of the {base type
definition} is a prefix of the {assertions} of the complex type definition
itself.

This constraint appears to be true by definition.

Conversely, the rules for type subsumption (Schema Component Constraint:
Complex type definition actually restricts) make no mention of any requirement
for the assertions on B to be a superset of those on R. This is where the rule
should appear.

A couple of other points: (a) defining a subset relation on sets of assertions
assumes the existence of an equality relation on assertions, and therefore on
XPath expressions, which has not been defined; (b) modelling the set of
assertions as an ordered list and requiring a sublist rather than subset
relationship seems to be a quite unnecessary complication - as with the rules
for deriving any from sequence, it seems to be a rule articulated by an
unimaginative implementer who knows how to handle lists and doesn't know how to
handle sets.

Received on Monday, 5 March 2007 22:39:48 UTC