Thanks, Joe –
That reflects
our current thinking (although I'd happily discuss alternate viewpoints).
This seems
to be a fairly clean and well-defined approach. My concern, which I hope the
membership can address, would be the ramifications on application builders. Is
it easier or harder to migrate both the vocabulary and the namespace names?
Of course,
this depends on the application architecture. And if one uses some form of
mapping middleware, it would also depend on the tools' handling of namespaces
(which is one of the many Schema capabilities that middleware vendors are scurrying
to accommodate).
Anybody
have any insights on this?
Thanks,
Mark
-----Original
Message-----
From: CHIUSANO, Joseph
[mailto:JCHIUSANO@lmi.org]
Sent: Tuesday, July 16, 2002 6:31
PM
To: Mark Feblowitz; 'Xml-Dev
(E-mail)'
Cc: Duane Krahn (E-mail); Satish
Ramanathan (E-mail); Andrew Warren (E-mail); Kurt A Kanaskie (Kurt) (E-mail);
Michael Rowell (E-mail)
Subject: RE: [xml-dev] Schema
Namespace name, schemaLocation, and Schema V ersioning
Mark,
I too have spent time thinking about this
very issue. I would say that if your namespace is associated with an XML
vocabulary, then changes in the namespace identifier could be in sync with
changes in the vocabulary - that is, if a construct has two different
"treatments" in two different "versions" of the vocabulary
(by that I mean perhaps a later version adds additional elements to a content
model), or new constructs are added to the vocabulary, then the namespace
identifier could change in some way to reflect the new version of the
vocabulary. If, however, there are X schemas that are all based on the
same version of a vocabulary, then I would say the namespace identifier should
remain the same, but the version information could be reflected in the schema
filename.
Hope that helps,
Joe Chiusano
LMI
>
**************************************************************************
> Joseph M. Chiusano
> Logistics Management Institute
> 2000 Corporate Ridge
> McLean, VA 22102
> Email: jchiusano@lmi.org
> Tel: 571.633.7722
>
**************************************************************************
>
-----Original Message-----
From: Mark Feblowitz [mailto:mfeblowitz@frictionless.com]
Sent: Tuesday, July 16, 2002 5:04 PM
To: 'Xml-Dev (E-mail)'
Cc: Duane Krahn (E-mail); Satish Ramanathan (E-mail); Andrew
Warren
(E-mail); Kurt A Kanaskie (Kurt) (E-mail); Mark Feblowitz; Michael
Rowell (E-mail)
Subject: [xml-dev] Schema Namespace name, schemaLocation, and
Schema
Versioning
I've read the Best Practice, debated the
pros and cons, and am still not
confident that I understand all of the ramifications: How should I
associate
evolving schema version numbers into my namespace name? Into my
schemaLocation?
I have a set of schemas, all under the
same namespace name, that will
certainly change over time.
Some changes will be major, some minor,
some "trivial" (with numbering
reflecting the various levels, e.g., 2.3.1).
I know that if I want validators to
validate the content, without writing
custom code that inspects the xml doc's content, the doc's
schemaLocation
must reflect the specific version information (e.g.,
http://www.MyStandard.org/2.3.1/xyz.xsd).
I know that each schema change could
affect the content in the instance
documents (changing the wire signature), and/or the names and/or
structure
of the schema, which could adversely affect those schemas that
import or
include the altered schema.
As such, each change reflects a different
version of the schema (and thus a
new schemaLocation, e.g., http://www.MyStandard.org/2.3.1/xyz.xsd).
But does each change warrant a new
namespace name?
How much of a change to the schema truly
warrants a change to the namespace
name? (Some say: "any change." Some say: "only
non-backward-compatible
changes," whatever those might be).
What are the ramifications of fine-grained
versioning in the schema
namespace (e.g., http://www.MyStandard.org/2.3.1/xyz.xsd)?
What are the ramifications of
course-grained versioning in the schema
namespace (e.g., http://www.MyStandard.org/2.3/xyz.xsd)?
With well-componentized schemas, I
understand that every change to the
schema would require a change to the namespace declaration in
every included
schema, in order for namespace names to match. With a good
configuration
management system, this can be supported trivially. For those who
don't use
these tools, this can be tedious and error prone.
I can tell you at the moment, I'm leaning
toward having three levels of
version numbering, and only reflecting major and minor version
numbers into
the namespace name. But as I said, I'm not confident about the
distinction
between "minor" and "trivial," nor am I
convinced that there would be no
adverse impacts on the schemas' deployability/usability.
From a pure xml standpoint, my current
approach will work, although I'm
still unsure whether any change, no matter how trivial, would
represent both
an identical vocabulary (in the instances) and an identical
meta-vocabulary
(in/among the schemas).
But from a practical, production
perspective, I am unsure how the
schema-consuming middleware would accommodate the changing
namespace names.
Certainly, new maps would have to be created for each
element/attribute in
each new namespace name. Not so for most of the content, if the
namespace
name was held stable and the predominant changes were extensions.
So what's your take ?( I know this is more
of a philosophical rather than
pure technical question). When should a namespace name change to
reflect
changes in the schemas? What granularity do you recommend? What
practices
are so common that I should just accept them, even if they don't
fully
answer my (many) questions?
Where can I look, beyond the xfront site,
to get insight into common
practice, ramifications, etc.? Is this question better asked under
the
XML-Dev list?
Thanks,
Mark
Mark
Feblowitz
XML Architect
[t]
617.715.7231
[f] 617.495.0188
Frictionless Commerce Incorporated
[e]
mfeblowitz@frictionless.com <mailto:mfeblowitz@frictionless.com>
[w] http://www.frictionless.com
<http://www.frictionless.com>
[m] 400 Technology Square,
9th Floor
Cambridge, MA 02139
Open Applications Group Incorporated
[e]
mfeblowitz@openapplications.org
<mailto:mfeblowitz@openapplications.org>
[w] http://www.openapplications.org
<http://www.openapplications.org>
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