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RE: definition of forward compatible/backward compatible still an open problem [XMLVersioning-41 ISSUE-41]

From: Marc de Graauw <marc@marcdegraauw.com>
Date: Wed, 12 Sep 2007 23:11:15 +0200
To: "'Dan Connolly'" <connolly@w3.org>
Cc: "'David Orchard'" <dorchard@bea.com>, "'www-tag'" <www-tag@w3.org>, "'Rene'" <rene.spronk@ringholm.com>
Message-ID: <99911F2ED65D40648738F714ACBD7E85@Marc>

Dan Connolly:

| On Wed, 2007-08-29 at 17:49 +0200, Marc de Graauw wrote:
| [...]
| > The full formalization is available at:
| > http://www.marcdegraauw.com/2007/08/29/axioms-of-versioning/
| I took a look; it does look coherent, though it might
| take a lot of examples to motivate that much detail/complexity.
| I'm mulling it over.

I've written a new version of 'Axioms of Versioning'
[http://www.marcdegraauw.com/files/axiomsofversioning.html], see point 12
for new stuff. I extended the formalization to get a grasp of the concept of
'Semantic Backward Compatibility' in HL7v3, which I believe is flawed
(quote: "Objective of backward model compatibility is that a receiver
expecting an 'old' version will not misinterpret content sent from a new
version"). It seems to be the reverse of the position of the W3C TAG in
'Extending and Versioning Languages: Terminology', and the position I would
defend myself. I notified HL7 of this, and one of our Dutch HL7
representatives told me they were aware of the problem - I don't know
whether they will change their definitions or not.

Yet the interaction of new senders with old receivers, which HL7 rightly
studies, was not sufficiently explored in my post. It turns out that
exploration of this notion leads to quite natural definitions of 'may
ignore' and 'must understand' semantics. The HL7v3 notion is probably best
characterized by the concept of 'partial semantical forward compatibility'
in my new Axioms. The concept is also close to, if not the same as, the
TAG's 'Partial Understanding'.


Received on Wednesday, 12 September 2007 21:11:32 UTC

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