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RE: Versioning of XML Schema and namespaces

From: Hans Teijgeler <hans.teijgeler@quicknet.nl>
Date: Mon, 9 May 2005 10:38:54 +0200
Message-Id: <200505090839.j498cvgC007480@vmx30.multikabel.net>
To: "'Michael Kay'" <mike@saxonica.com>, <John.Hockaday@ga.gov.au>, <xmlschema-dev@w3.org>


In the case I painted the schemas found in the schemalocation are normative,
and we'd rather not that prople work from local copies that get out of date.


-----Original Message-----
From: xmlschema-dev-request@w3.org [mailto:xmlschema-dev-request@w3.org] On
Behalf Of Michael Kay
Sent: maandag 9 mei 2005 10:10
To: John.Hockaday@ga.gov.au; xmlschema-dev@w3.org
Cc: ":www-xml-schema-comments"@w3.org
Subject: RE: Versioning of XML Schema and namespaces

Personally I think the combination of a namespace and a version attribute in
the document element is a better way of asserting conformance to a
particular version of an external standard than use of a schemaLocation. The
reason for that is that the semantics of xsi:schemaLocation as defined in
the XML Schema specification don't say it's an assertion about conformance,
they say it's a hint about where to find a schema to use for validation.  I
think it's a mistake to overlay different semantics onto an attribute
outside your control; and more practically, using this attribute as a
conformance assertion prevents people using it to point to a local copy of a

Michael Kay

> -----Original Message-----
> From: John.Hockaday@ga.gov.au [mailto:John.Hockaday@ga.gov.au]
> Sent: 09 May 2005 01:24
> To: mike@saxonica.com; xmlschema-dev@w3.org
> Cc: ":www-xml-schema-comments"@w3.org
> Subject: RE: Versioning of XML Schema and namespaces
> Michael,
> Thanks for your comments.  Please see below one aspect that I disagree 
> with.
> Thanks to you all for being patient and contributing to this 
> discussion.
> John
> > -----Original Message-----
> > From: Michael Kay [mailto:mike@saxonica.com]
> > Sent: Friday, 6 May 2005 8:26 PM
> > To: Hockaday John; xmlschema-dev@w3.org
> > Cc: ":www-xml-schema-comments"@w3.org
> > Subject: RE: Versioning of XML Schema and namespaces
> > 
> > 
> > ....
> > 
> > I wouldn't expect the instance document to contain a schemaLocation 
> > attribute, or if it does, I wouldn't expect a recipient to trust it 
> > when doing validation. If say the sender has decided to leave out 
> > some mandatory elements, and to create a local copy of the schema 
> > that makes them optional, you as the recipient don't want validation 
> > to succeed.
> > 
> The metadata gateway that I manage will be able to search metadata of 
> multiple types.  For example; ANZLIC version 2 defined by 
> http://www.environment.gov.au/net/dtd/anzmeta-1.3.dtd , extensions to 
> this standard such as 
> http://www.indexgeo.net/dtd/anzmeta-resource-v11.dtd and 
> http://www.gso.qld.gov.au/qsiis/dtd/qsiis-1.3.dtd
> or ISO 19139 metadata records including extensions of that standard, 
> which are yet to be defined.
> If I download an XML metadata record (document instance) I don't know 
> what standard I should validate it against unless there is a DOCTYPE 
> or schemaLocation declaration.  I therefore can't validate that 
> document without this information.  I believe that *every* XML 
> document instance should have either a DOCTYPE or a schemaLocation so 
> that anyone who wants to look at this instance knows with what XSD it 
> complies.  One may not wish to validate the document but if one wants 
> to use the document then he or she needs to know what this document is 
> about.  That can only be rigorously identified by a DOCTYPE or 
> schemaLocation declaration.
> Furthermore, I agree that if a "mandatory" element in an extension of 
> the ISO
> 19139 metadata standard has been redefined as "optional" then 
> validation should ignore that change. However, by definition of the 
> extensibility of the ISO 19115 metadata standard, an "optional" ISO 
> 19139 element can be made "mandatory" in an extension of that XSD for 
> an organisation's or country's need.  Therefore, one *must* use that 
> extension when validating an XML document instance of that XSD type to 
> check that it meets those needs.  The only way I know of to identify 
> that extension is from a schemaLocation declaration and therefore is 
> it necessary to validate that XML document instance.
> Public identifiers were great.  There was only the need for one 
> DOCTYPE declaration in an XML document instance.  It was the inclusion 
> of the original DTD in the DTD identified by the DOCTYPE that defined 
> the extension.
> It wasn't necessary to have the original DTD identified in the XML 
> document instance.
> However, and I'm not sure about this, it seems that if one extends a 
> W3C XML Schema then one needs to not only identify the new XSD via a 
> namespace but one also needs to include the original XSD that has been 
> extended.  If this is so then XML document instances can become *very* 
> messy when there is an extension of an extension of an extension etc..
> Thanks for your time.
> J.H.
> > Michael Kay
> > http://www.saxonica.com/
> > 
> > 
> > 
Received on Monday, 9 May 2005 08:39:33 UTC

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