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

From: Dan Connolly <connolly@w3.org>
Date: Fri, 24 Aug 2007 16:57:37 -0500
To: www-tag <www-tag@w3.org>
Message-Id: <1187992657.29837.1626.camel@pav>

The July 4 draft has a revised definition of information
compatibility in response to my [21Aug] comments on the
defintion of forward/backward compatibility of languages:

* Let I1 be the information conveyed by Text T per language L1. 

  * Let I2 be the information conveyed by Text T per language L2. 

  * I1 is compatible with I2 if all of the information in I1 does not
    replace or contradict any information in I2.
 -- http://www.w3.org/2001/tag/doc/versioning

But it still defines compatibility of languages in terms
of compatibility of information in a way that doesn't appeal
to me.

That definition of compatibility of information reminds me
of the conventional definition of consistency:

A theory is said to be satisfiable if it has a model. A theory is
consistent if its closure (under the usual rules of inference) does not
contain a contradiction. One way of stating the completeness theorem is
the following: A theory is satisfiable if and only if it is consistent.
 -- http://en.wikipedia.org/wiki/Model_theory

... but there a theory is a text. I'm not familiar with any definition
of consistency/compatibility of stuff that the text refers to, i.e.
"the information conveyed by a text."

I was part way working thru mappings back in September:

Re: Re-expressing our formalisation of Language

But I didn't really see how to finish it. And neither did Henry
nor Pat Hayes.

This still feels like an open research problem, to me.

p.s. Hi tracker. This is progress on, if not completion of, ACTION-4

[21Aug] http://lists.w3.org/Archives/Public/www-tag/2006Aug/0084

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 24 August 2007 21:57:54 UTC

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