Hi All,

First of all thanks to all those quick and informative responses.  =
Secondly,
sorry for getting my syntax wrong.  I should have used "schemalocation"
instead of "namespace".  Thanks to Eliot for sorting this out for me.  =
;--)

Eliot mentions:

> But, a processor could use other 
> heuristics to decide
> which version to use, for example, looking in the document 
> for other clues
> or using some outside information, such as metadata held in a document
> management system.
> 

The problem is that the XML document instances will be ISO 19139 =
metadata.
They are the only clues that I will have.  ISO 19139 will be extensible =
and I
expect that agencies will extend the XSDs to suit their own needs.  I =
need to
know that there is a difference and therefore I can track down the true
values.

I found that the first draft of ISO 19139 was not valid.  It hopefully =
will
be valid in the final release.  The other problem is that I don't have
control over how ISO 19139 identifies its schemalocation.  Can I trust =
that
an International Standard will have versions in its schema locations?  I
don't think so if it isn't valid in the first place.  What happens when =
there
are changes the XML Schema?  ;--)

Paul writes:

> Depending on circumstances, it can be very dangerous to 
> trust the sender/author to tell you what DTD/schema to use 
> to validate against.  After all, one of the main reasons 
> to perform validation is because you don't trust the 
> sender/author...so why would you trust them when they 
> tell you what DTD/schema to use?

I have found that many people don't understand how to properly use XML.  =
They
have tools that generate XML and trust that it is right.  I have found =
that
if I try to validate that XML I find it is not valid.  The users don't
understand why.  They have relied on the vendor's statements which may =
not be
100% true.  For example, Xerces literally interprets the W3C XML Schema
whereas XMLSpy">XMLSpy seems to have a more lax interpretation.  Many people =
have
said that their XML validated using XMLSpy">XMLSpy but when I use Xerces it =
isn't
valid.  No-one seems to be telling the vendors that their products are =
not
right.

I also find that some W3C XML Schema are not valid according to Xerces.  =
If
the XSD is not valid then how can I expect to validate the XML documents
which use that XSD?  Hopefully I won't have to use these problematic =
XSDs but
the problem still may occur.

When an organisation extends the ISO 19139 metadata XSD I need to check =
to
see if they have got it right.  But I don't know about the new XSDs =
unless
they are referenced in the XML document instances which I download each
quarter.  I can then locate and validate the XSD which are referenced in =
the
schemalocation in the XML documents and then validate the XML document
instances themselves.  I then report my findings to the managers of =
those
metadata entries.  It's not that I can't trust the owners of the =
documents.
It's that they don't know the right way to do things so I tell them when =
they
are wrong so that they can fix the problem.

I have also found that they may have relative URIs for the schema =
locations
in their XML document instances.  This makes everything difficult to =
solve.
I have to contact the owner of the document and tell them to use =
absolute
schema locations so that I can validate their XML document or track down =
a
new XSD.

I have found that if the XML documents are not valid then searches on =
those
documents will not return appropriate results.  For example, the date =
format
of the XML document instances are supposed to be ISO 8601 compliant yet =
some
content still looks like "27-Jan-2005" or some other non-ISO 8601 =
format.
The indexes of these fields don't check the format but when a search for
dates between "2005 and 2006" are sent to these indexes, the document
containing a date of "27-Jan-2005" is not returned.  Hence the search =
tool is
not effective because of the XML content.  This is why I have to =
validate the
XML documents that are made available via our metadata search tool.   I =
can't
trust that the XML document nor the XSDs are correct but I can if I =
validate
them myself.

I have no control over some of the schemalocation definitions.  For =
example,
xlink, GML, ISO 19139 and any extensions of the latter.  

Eliot writes:

> It's important to remember that there is (and never was) any =
particular 
> magic to PUBLIC identifiers--they are just magic strings that require 
> indirection to be resolved. In that respect that are indistinguishable =

> for URIs that also require indirection to be resolved to real =
resources.

I know that Public Identifiers are not magic but for some reason it =
seems
that Public Identifiers are more likely to be genuinely unique for =
different
versions of XSDs than URIs and therefore I would like to see a similar
solution.

Thanks again for prompt replies and the helpful discussions.


John
 
> -----Original Message-----
> From: Hans Teijgeler [mailto:hans.teijgeler@q...] 
> Sent: Thursday, 5 May 2005 8:53 AM
> To: 'Hans Teijgeler'; 'Eliot Kimber'; Hockaday John; 
> xmlschema-dev@w...
> Cc: ":www-xml-schema-comments"@w3.org
> Subject: RE: Versioning of XML Schema and namespaces
> 
> 
> I don't know what software is used for this forum. My neatly arranged
> listings got garbled. Still readable, I hope.
> Hans
> 
> -----Original Message-----
> From: xmlschema-dev-request@w... 
> [mailto:xmlschema-dev-request@w...] On
> Behalf Of Hans Teijgeler
> Sent: donderdag 5 mei 2005 0:25
> To: 'Eliot Kimber'; John.Hockaday@g...; xmlschema-dev@w...
> Subject: RE: Versioning of XML Schema and namespaces
> 
> 
> Hi John,
> 
> My two cents of wisdom. In ISO 15926-7 we have defined nine 
> interlinked XML
> Schemas, the top one, for the data ISO 15926-2 data model, 
> starting with:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <xs:schema 
> 	xmlns:xs="http://www.w3.org/2001/XMLSchema" 
> =09
> xmlns="http://www.tc184-sc4.org/iso15926-7/datamodel/2005-1.xsd" 
> =09
> targetNamespace="http://www.tc184-sc4.org/iso15926-7/datamodel
> /2005-1.xsd" 
> 	elementFormDefault="qualified" 
> attributeFormDefault="unqualified">
> 	...
> 
> This is imported in the next level schema, for Templates:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <xs:schema 
> =09
> xmlns="http://www.tc184-sc4.org/iso15926-7/templates/2005-1.xsd" 
> =09
> xmlns:p2="http://www.tc184-sc4.org/iso15926-7/datamodel/2005-1.xsd" 
> 	xmlns:xs="http://www.w3.org/2001/XMLSchema" 
> =09
> targetNamespace="http://www.tc184-sc4.org/iso15926-7/templates
> /2005-1.xsd" 
> 	elementFormDefault="qualified" 
> attributeFormDefault="unqualified">
> 	<xs:import
> namespace="http://www.tc184-sc4.org/iso15926-7/datamodel/2005-1.xsd" =

> =09
> schemaLocation="http://www.tc184-sc4.org/iso15926-7/datamodel/
> 2005-1.xsd"/>
> 	...
> 
> and this is imported again in the next level, for Object 
> Information Models:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <xs:schema 
> 	xmlns="http://www.tc184-sc4.org/iso15926-7/oim/2005-1.xsd" 
> =09
> xmlns:p2="http://www.tc184-sc4.org/iso15926-7/datamodel/2005-1.xsd" 
> =09
> xmlns:templ="http://www.tc184-sc4.org/iso15926-7/templates/200
> 5-1.xsd" 
> 	xmlns:xs="http://www.w3.org/2001/XMLSchema" 
> =09
> targetNamespace="http://www.tc184-sc4.org/iso15926-7/oim/2005-1.xsd"
> 
> 	elementFormDefault="qualified" 
> attributeFormDefault="unqualified">
> 	<xs:import
> namespace="http://www.tc184-sc4.org/iso15926-7/datamodel/2005-1.xsd" =

> =09
> schemaLocation="http://www.tc184-sc4.org/iso15926-7/datamodel/
> 2005-1.xsd"/>
> 	<xs:import
> namespace="http://www.tc184-sc4.org/iso15926-7/templates/2005-1.xsd" =

> =09
> schemaLocation="http://www.tc184-sc4.org/iso15926-7/templates/
> 2005-1.xsd"/>
> 
> etc, etc.
> 
> The targetNamespace contains (here) the suffix 2005-1, 
> meaning that it is
> the first version of the year 2005. The schemas are (in due 
> time) located on
> a publicly accessible web server.
> 
> I hope this helps somewhat.
> 
> Regards,
> Hans
>  
> 
> -----Original Message-----
> From: xmlschema-dev-request@w... 
> [mailto:xmlschema-dev-request@w...] On
> Behalf Of Eliot Kimber
> Sent: woensdag 4 mei 2005 17:11
> To: John.Hockaday@g...; xmlschema-dev@w...
> Cc: ":www-xml-schema-comments"@w3.org
> Subject: Re: Versioning of XML Schema and namespaces
> 
> 
> John.Hockaday@g... wrote:
> > I expect that document instances using W3C XML Schemas will use a
> "namespace"
> > declaration to identify which XML Schema should be used to validate 
> > that document instance.  The problem that I see with the 
> namespace it 
> > that a URI is the unique identifier.  There is no PUBLIC identifier.
> > As we have all probably experienced with old bookmarks, the 
> content at
> URLs change a lot.
> > If an XML Schema's version is not part of the URI and a new 
> version of 
> > that XML Schema is made then it is likely that this will *not* be 
> > reflected in the URI and hence the namespace.
> 
> I think you're confusing two similar but distinct functions here: 
> namespaces and schema locations. DTD declarations with 
> external identifiers
> are equivalent to schemaLocation specifications, not namespace
> declarations--SGML (and XML without namespaces) had no equivalent of
> namespaces [except for HyTime architectures].
> 
> For DTDs, which are a syntactic part of the document that 
> references them,
> the PUBLIC identifier is nothing more than an alias for the 
> external DTD
> subset's storage location (i.e., it's filename). Thus it is completely
> appropriate that it include a version identifier since if the external
> declaration subset is changed it's a new object and should be 
> identified as
> such.
> 
> By contrast, a document's namespace *does not* directly 
> identify a schema.
> It identifies (or rather, can be exclusively associated with) an
> (abstract) "application" that might have any number of 
> schemas associated
> with it. That is, for a given application, with a single associated
> namespace, there might be different schemas *at the same 
> time*, reflecting
> different profiles or uses of the application, or there might 
> be different
> schema versions over time reflecting changes over time to the 
> details of the
> namespace. But the namespace itself is unchanged because the namespace
> identifies the application independent of it's various 
> implementations over
> time. [For example, the XSLT namespace is invariant across 
> versions of the
> XSLT spec because, as an abstract application, XSLT is XSLT 
> regardless of
> the currently-defined details of it.]
> 
> In DTD-based documents that use external declaration subsets 
> you always have
> to have an external identifier for the subset, so you always 
> had something
> you could resolve or use in a catalog.
> 
> For non-DTD-based documents, there are two possible cases (assuming
> namespaced documents--the no-namespace case is degenerate and 
> not worth
> considering because it allows no good general solution):
> 
> 1. The document uses the schemaLocation= hint to say which 
> specific schema
> it wants you to use.
> 
> 2. The document specifies only a namespace.
> 
> In the first case, the schema location can either be local, 
> relative URI or
> it can be an absolute URI. In this case of the absolute URI, the URI
> functions essentially as a PUBLIC ID does: it essentially 
> demands local
> mapping to a local resource via some sort of catalog method 
> (for the simple
> practical reason that most processing environments aren't always net
> connected or because the schema is not in fact served on a
> publicly-available server). If the absolute URI includes some sort of
> version value, then you have *exactly the same* functionality 
> and semantics
> as with PUBLIC IDs for external DTD subsets.
> 
> In the second case, the implication is that the system must 
> determine which
> version of the schema to use, which typically would be done 
> using a catalog
> and probably implies that in most cases you want the latest 
> or more general
> version of the schema. But, a processor could use other 
> heuristics to decide
> which version to use, for example, looking in the document 
> for other clues
> or using some outside information, such as metadata held in a document
> management system.
> 
> Thus, I think the appropriate approach in your case is to 
> require the use of
> schemaLocation= with absolute URIs that include version 
> information--that
> gives you the same control you had before.
> 
> It's important to remember that there is (and never was) any 
> particular
> magic to PUBLIC identifiers--they are just magic strings that require
> indirection to be resolved. In that respect that are 
> indistinguishable for
> URIs that also require indirection to be resolved to real resources.
> 
> Cheers,
> 
> Eliot
> 
> --
> W. Eliot Kimber
> Professional Services
> Innodata Isogen
> 9390 Research Blvd, #410
> Austin, TX 78759
> (512) 372-8155
> 
> ekimber@i...
> www.innodata-isogen.com
> 
> 
> 
> 

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