[Bug 4338] Redefining attribute groups and model groups

http://www.w3.org/Bugs/Public/show_bug.cgi?id=4338

           Summary: Redefining attribute groups and model groups
           Product: XML Schema
           Version: 1.0/1.1 both
          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 specification for "redefines" in 4.2.2 states:

"In order to provide some support for evolution and versioning, it is possible
to incorporate components corresponding to a schema document with
modifications. The modifications have a pervasive impact, that is, only the
redefined components are used, even when referenced from other incorporated
components, whether redefined themselves or not."

There are many difficulties in understanding this text, centering around the
word "pervasive". The use of "even when" suggests an example rather than a
definitive statement of what "pervasive" means. However, the clear implication
is that any schema component A that refers to a schema component B that has
been redefined as B' is taken as referring to B'.

However, this intepretation doesn't work for attribute groups and model groups,
because no schema component ever contains a reference to an attribute group
definition or a model group definition. Perhaps this is why we read in the note
"The pervasive impact of redefinition reinforces the need for implementations
to adopt some form of lazy or 'just-in-time' approach to component
construction". The implication of this note is presumably that conversion of
the information in a schema document to a schema component is done as late as
possible. Presumably once this conversion has been done, subsequent
redefinition of components will have no effect (at any rate in the case of
model groups and attribute groups, but perhaps in other cases too).

In any case, the phrase "referenced from other incorporated components" seems
wrong. It is references from schema documents that are redirected, not
references from schema components. Once the schema components have been built,
there is no reference to any attribute group or model group definition, so no
redirection is possible.

Received on Wednesday, 21 February 2007 08:23:09 UTC