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RE: No Standard way to reference XML Schema? Was Re: (Many) XML S chema Questions

From: Andrew Layman <andrewl@microsoft.com>
Date: Thu, 30 Dec 1999 14:05:16 -0800
Message-ID: <33D189919E89D311814C00805F1991F7F4AAF4@RED-MSG-08>
To: "'Bob Kline'" <bkline@rksystems.com>, "Roger L. Costello" <costello@mitre.org>
Cc: xml-dev@ic.ac.uk, www-xml-schema-comments@w3c.org, "Schneider,John C." <jcs@mitre.org>, "Cokus,Michael S." <msc@mitre.org>
A standard does not necessarily preclude choices or optional processing
decisions by an application; it frequently sets bounds within which options
may be chosen; often the freedoms permitted by a standard are as important
as the freedoms removed.  For example, HTML allows different user agents to
render the same document differently.

I agree with your intuitive suspicion that readers of a document ought to be
reading what the author intended, and that a large part of an author's
intention is revealed in his warrants about schema conformance.  But the
question is: How does this get expressed in the rules of the schema
standard?  The schema WG debated this extensively (often with me taking the
side you are now arguing!) but in the end decided that applications need the
flexibility, in some cases, to ignore the schemas recommended by the
document and use either none or others.  In fact, if a (probably
namespace-qualified) information item is associated by an application with
certain semantics, then the document's claims about schema conformance may
be simply irrelevant.

-----Original Message-----
From: Bob Kline [mailto:bkline@rksystems.com]
Sent: Thursday, December 30, 1999 5:03 AM
To: Roger L. Costello
Cc: xml-dev@ic.ac.uk; www-xml-schema-comments@w3c.org; Schneider,John
C.; Cokus,Michael S.
Subject: Re: No Standard way to reference XML Schema? Was Re: (Many) XML
Schema Questions

On Thu, 30 Dec 1999, Roger L. Costello wrote:

> I read these statements as saying that there is no standard way for
> specifying in an XML document what XML Schema it conforms to - every
> XML Parser will have its own way of doing things.  Really???  If
> this is so, please, please tell me why this is a good thing.  I am
> struggling to appreciate its beauty.  /Roger

I am as puzzled as you are.  Yes, it's true, as Andrew writes, that
"ultimately, the processor of a document determines what processing is
done" [cited as the rationale for the decision by the XML Schemas WG to
demote the xsi:schemaLocation attribute to a "hint"].  The same could be
said of any software, which behaves in direct response to the
instructions written by its creators, rather than the prescriptions of
standards.  The role of a standard is to assist in the processes of
predicting how software which claims conformance to it will behave, and
of determining which products are actually conformant.

Bob Kline

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Received on Thursday, 30 December 1999 17:07:27 UTC

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