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LC-182 single-binding rule

From: C. M. Sperberg-McQueen <cmsmcq@acm.org>
Date: Mon, 09 Oct 2000 21:15:43 -0600
Message-Id: <4.3.2.7.1.20001009211502.025657d8@espanola.com>
To: Philip Wadler <wadler@research.bell-labs.com>, Paul Cotton <pcotton@microsoft.com>, W3C XML Query WG <w3c-xml-query-wg@w3.org>
Cc: W3C XML Schema Comments list <www-xml-schema-comments@w3.org>
Dear Philip, Paul, and members of the XML Schema WG:

The W3C XML Schema Working Group has spent the last several months
working through the comments received from the public on the last-call
draft of the XML Schema specification.  We thank you for the comments
you made on our specification during our last-call comment period, and
want to make sure you know that all comments received during the
last-call comment period have been recorded in our last-call issues
list (http://www.w3.org/2000/05/12-xmlschema-lcissues).

Among other issues, you raised the point registered as issue LC-182,
which suggests that XML Schema be modified to relax the rule which
currently requires that within a given complex type, any generic
identifier (aka 'tag name' or 'element type name') be bound to at most
one datatype.  This means, in effect, that the binding between an
element and a type be fully determined by the ancestry of the element,
and not by its left siblings.

Some members of the WG would like, with you, to eliminate this rule,
in theory, but fear that in practice it would complicate things too
much.  Other members of the WG would not like to eliminate this rule
because they believe that eliminating it would also make it
impossible, in practice, to eliminate the deterministic-content-model
rule and thus define complex types which are closed under union,
intersection, set difference, etc.

It may also be observed that this rule is necessary to ensure that
fully- or partially-qualified GIs of the kind found in the path
expressions of XML Query's algebra are uniquely associated with a type.

The upshot is that the WG declined to make the change.

It would be helpful to us to know whether you are satisfied with the
decision taken by the WG on this issue, or wish your dissent from the
WG's decision to be recorded for consideration by the Director of
the W3C.

with best regards,

-C. M. Sperberg-McQueen
  World Wide Web Consortium
  Co-chair, W3C XML Schema WG
Received on Monday, 9 October 2000 17:18:27 GMT

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