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

From: Roger L. Costello <costello@mitre.org>
Date: Thu, 30 Dec 1999 07:03:49 -0500
Message-ID: <386B4A25.1D34E681@mitre.org>
To: xml-dev@ic.ac.uk
CC: www-xml-schema-comments@w3c.org, "Schneider,John C." <jcs@mitre.org>, "Costello,Roger L." <costello@mitre.org>, "Cokus,Michael S." <msc@mitre.org>
Hi Folks,

I gotta tell ya, this 'ol country boy is having a mighty difficult time
figuring out how an XML document is to indicate to that it conforms to
a  particular XML Schema.  It seems to me that this should be one area
that should be made crystal clear.  Instead, I am finding this to be one
of the murkiest parts of the XML Schema spec.

These statements really throw me through a loop:

"xsi:schemaLocation attribute serves as a hint, not a mandatory
directive. That is, the processor of an instance is welcome to look at
the URI referenced by the value of xsi:schemaLocation, but is not
required to."

"The means used to locate appropriate schema document(s) are processor
and application dependent"

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

Andrew Layman wrote:
> 
> What was said by Rick Jeliffe regarding the current schema draft is true
> (and anyone who is interested is recommended to red the actual XML Schema WD
> at http://www.w3.org/TR/xmlschema-1/ and http://www.w3.org/TR/xmlschema-2/.)
> 
> However, I would like to correct a possible misimpression that might arise
> from the turgid wording in the current public draft and also from Rick's
> statement "Then (s4.3.2) there is an attribute xsi:schemaLocation that can
> be put on any instance element. It allows the location of the schema to be
> declared. ..."
> 
> After extensive debate, the XML Schemas WG decided that the
> xsi:schemaLocation attribute serves as a hint, not a mandatory directive.
> That is, the processor of an instance is welcome to look at the URI
> referenced by the value of xsi:schemaLocation, but is not required to.  It
> may process an instance document using a different schema set (or no schemas
> at all).  The relevant phrase is "unless directed otherwise" in the
> following passage from the 1999-12-17 structures draft:
> 
> "Again, unless directed otherwise general-purpose schema-aware processors
> must attempt to dereference each schema URI in the value of "schemaLocation"
> to obtain a schema..."
> 
> This is in recognition of the fact that, ultimately, the processor of a
> document determines what processing is done.
> 
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Received on Thursday, 30 December 1999 07:02:32 UTC

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