W3C home > Mailing lists > Public > xmlschema-dev@w3.org > February 2001

Re: Bug in XSV?

From: Robert Tiess <rjtiess@warwick.net>
Date: Mon, 26 Feb 2001 23:51:46 -0500
Message-ID: <3A9B3262.7D0E058D@warwick.net>
To: xmlschema-dev@w3.org
"Henry S. Thompson" wrote:
>  No, it's a real bug, now fixed but not released.

Thanks for verifying that.  Just wondering.

"Henry S. Thompson" wrote:
>  Nothing in an XML Schema implementation should
>  be order dependent, since nothing in XML Schema
>  itself is.

I understand and agree concerning implementation.
Yet, while the example we dealt with illustrates
order independence of XML Schema, there are, as
we know, obvious needs within schema structures 
for order such that implementation (say a third
party validating schema parser) enforces order,
as in the clear case of model groups (sequences,
namely) or other statements in XML Schema docs,
such as XML Schema Part 0: "Primer, 2.5.2 Mixed
Content" ("Under the XML Schema mixed model, the
order and number of child elements appearing in
an instance must agree with the order and number
of child elements specified in the model") and
XML Schema Part 1: Structures:  "Constraint on
Schemas: Particle Derivation OK
(All:All,Sequence:Sequence -- Recurse)":
"Although the validation semantics of an all
group does not depend on the order of its
particles, we require derived all groups to match
the order of their base to simplify checking that
the derivation is OK."  XML Schema Part 2:
Datatypes "2.5.1.3 Union datatypes" also suggests
implementational significance of order:  "The
order in which the memberTypes are specified in
the definition (that is, the order of the
<simpleType> children of the <union> element, or
the order of the QNames in the memberTypes
attribute) is significant. During validation, an
element or attribute's value is validated against
the memberTypes in the order in which they appear
in the definition until a match is found."

Omniscience should be attainable in hypothetical
schema applications upon receipt of a valid and
well-formed schema, so complexTypes occurring
before or after element declarations are resolved
respectively; omniscient yet scoping validators.
Beyond this, stylistic, logical, and organizational
issues arise.  In terms of clarity, the XML Schema
doc examples provide excellent models for breaking
down complex structures into legible units.  The
freedoms Schema endows are many and wonderful,
provided implementations will competently parse
them and the schemas themselves will have been
clearly conceived, complex only as was necessary
to accommodate their anticipated data.

Robert Tiess
rjtiess@warwick.net
http://rtiess.tripod.com
Received on Monday, 26 February 2001 23:42:42 UTC

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