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Re: Redefining redefines

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 14 Feb 2002 12:07:54 +0000
To: Mark Feblowitz <mfeblowitz@frictionless.com>
Cc: xmlschema-dev@w3.org, support@xmlspy.com, www-xml-schema-comments@w3.org
Message-ID: <f5br8nol10l.fsf@cogsci.ed.ac.uk>
Mark Feblowitz <mfeblowitz@frictionless.com> writes:

> There are situations in which the redefinition of a type, and the subsequent
> redefinition of the redefined type, are desirable. One such case is where a
> schema user would like to extend a type, not just from the original source
> but based on the extension of another schema user's extension (Company C
> extends type T from Company B, who picked it up from Company A and redefined
> it). 
> I notice in the Rec that this is discouraged:
> In all cases there must be a top-level definition item of the appropriate
> name and kind in the <redefine> <http://www.w3.org/TR/xmlschema-1/> d schema
> document. 
> 		NOTE: The above is carefully worded so that multiple
> equivalent <redefine> <http://www.w3.org/TR/xmlschema-1/> ing of the same
> schema document will not constitute a violation of clause 2
> <http://www.w3.org/TR/xmlschema-1/>  of Schema Properties Correct (3.15.6)
> <http://www.w3.org/TR/xmlschema-1/> , but applications are allowed, indeed
> encouraged, to avoid <redefine> <http://www.w3.org/TR/xmlschema-1/> ing the
> same schema document in the same way more than once to forestall the
> necessity of establishing identity component by component (although this
> will have to be done for the individual redefinitions themselves).
> Indeed, XML Spy requires that the redefined schema contain a type definition
> for a type that is to be redefined - that a redefinition is not sufficient.
> So it is not possible to redefine a redefined type.
> So the question is, is this something that is likely to change, or will
> validators vary on whether or not they support cascading redefines?

Unfortunately the term 'top-level' is not formally defined in the
REC.  There are a number of places where things such as "all the
top-level (i.e. named) components. . ." appear, so it's clear that
what's meant is (XML representations of) named components which appear
in one of the sets of definitions/declarations of the schema component
itself.  On that basis, redefs of redefs are OK, and were certainly
intended to be.  An erratum is in order, in my opinion.

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Thursday, 14 February 2002 07:08:01 UTC

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