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Re: Confused about name-space declarations..

From: Bob Schloss <rschloss@us.ibm.com>
Date: Fri, 5 Oct 2001 09:00:14 -0400
To: Ian Stuart <Ian.Stuart@ed.ac.uk>, xmlschema-dev@w3.org
Message-ID: <OF2040ACA4.6209B6AA-ON85256ADC.00463E6B@pok.ibm.com>

There are in practice 4 different treatments that processors make with
namespaces.

1. All schema-aware processors are hard coded to understand the namespaces
http://www.w3.org/2001/XMLSchema    and
http://www.w3.org/2001/XMLSchema-instance

2. Some schema-processors, using a default or user supplied EntityResolver,
which may reference some kind of catalog, attempt to discover the schema
components associated with a namespace by using the namespace name to find
the schema component definitions.  For whatever namespaces they do this
for, they ignore xsi:noNamespaceSchemaLocation or xsi:schemaLocation
attribute which may appear in instance documents, and they ignore
schemaLocation attributes of <import> <include> and <redefine> element
information items in any schemas they process.

3. Some schema-processors have Entity-Resolvers written so that if there
was no entry for a particular namespace in the catalog above,
will use the value specified in xsi:noNamespaceSchemaLocation, or in the
schemaLocation attribute of <import> <include> and <redefine>,
or as the second part of xsi:schemaLocation, as a URI and will use internet
protocols to fetch what is at that URI to find the schema component
definitions.

4. Some schema-processors have Entity-Resolvers written so that if there
was no entry for a particular namespace in the catalog above,
will dereference the namespace URI and if they receive a RDDL file, will
follow a link there to find a schema document.

     The schema spec offers to possibility of using schemaLocation URIs in
schemas that you write and instance documents that you write, so that
processors that do treatment 3 have something to work with.  But no
processor is obligated to use those URIs.  Thus, they are more like
"hints".
     BTW: I would like to see someone post somewhere a document which for
every open source or vendor produced schema-aware processor, information is
given about which treatments that processor uses, and what is the relative
priority between treatments 2, 3, and 4 if more than one is implemented.
No one has stepped forward to do this so far.

          Regards,
          Bob

Bob Schloss
IBM Thomas J. Watson Research Center
Yorktown Heights, New York, USA


Ian Stuart <Ian.Stuart@ed.ac.uk>@w3.org on 10/05/2001 03:22:55 AM

Sent by:  xmlschema-dev-request@w3.org


To:   XML-Schema-dev <xmlschema-dev@w3.org>
cc:
Subject:  Confused about name-space declarations..



Morning folks..

I thought, for a while, that I had the name-space declarations sussed:

You use one of the following formats:

xsi:NoNamespaceSchemaLocation = <URI_of_schema_file>

or

xmlns:MyNameSpaceTag = "<namespace URI>"
xsi:schemaLocation = "<namespace URI> <schema_file>"

or (I found out by accident)

if the schema has the same basename as the instance document *and* is in
the name directory - you don't need a declaration at all

HOWEVER:
Why to these work:

xmlns:xsd = "http://www.w3.org/2001/XMLSchema"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"

They make no reference to a file, and the "noNamespaceSchemaLocation"
attribute does not work without the :xsi declaration...

Any guidance/illumination greatfully recieved..

--
--==++
Ian Stuart: Edinburgh University Data Library.
I build things: computer programs (with code); or cars (with metal)

 Personal web site: http://lucas.ucs.ed.ac.uk/
Received on Friday, 5 October 2001 09:01:50 GMT

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