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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

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

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

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
     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.


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>
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>


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

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 UTC

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