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Re: Extension and Restriction of Wildcard Attribute

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 18 Dec 2000 14:39:14 +0000
To: "Asir S Vedamuthu" <asirv@webmethods.com>
Cc: www-xml-schema-comments@w3.org, "Ningang chen" <nchen@webmethods.com>
Message-ID: <f5bitohaj59.fsf@cogsci.ed.ac.uk>
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"Asir S Vedamuthu" <asirv@webmethods.com> writes:

> First, I would like to observe that extension of wildcard attribute is not
> the same as restriction of wildcard attribute. And, these two items are
> clearly under specified in the structures draft.

I agree that this needs clarification -- the hard subcase of
restriction and extension are not covered.

> In the structures draft, both extension and restriction of wild card
> attribute is described using an arbitrary intensional ( or in tensional :-/,
> Microsoft spell check accepts the latter) intersection [1x]. Nothing is
> specified in the context, extension or restriction. 
> For discussion, I use two complex types A and B. B is derived from A. These
> two types have wild card attributes in the surface syntax.
> [Case 1] B extends A. Spec says that the resulting wild card attribute of B
> is the arbitrary
> intersection of wild card attribute of A and B (found in surface syntax).

This is one case that's not covered -- it doesn't say anything at all
about this case.  Or rather, what it does say doesn't take account of
the base type's wildcard, if present.

> Proposed resolutions
> (a) Clearly specify what does extension or restriction of wild card
> attribute mean?

For sure.

> (b) If extension, it is the union of wild card attribute of A and B

Probably, yes, modulo the need to be able to express this.  What is
union of [not a] and [b c]?

> (c) If restriction, it is the intersection of wild card attribute of A and
> B, iff the result is the wild card attribute of B

Yes, I think so.

  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 Monday, 18 December 2000 09:39:20 UTC

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