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@s...] 
> Sent: Friday, 6 May 2005 8:26 PM
> To: Hockaday John; xmlschema-dev@w...
> 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/
> 
> 
> 

From mike@s... Mon May 09 08:10:16 2005
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