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   Re: Architectural Forms and XAF

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  • From: Sean McGrath <digitome@iol.ie>
  • To: xml-dev@XML.ORG
  • Date: Mon, 06 Mar 2000 09:50:57 +0000

[Steve Newcomb]
>Sean, somehow you've completely missed the point of AFs.

Always a possibility but I don't think so!

>  AFs are not
>about general transformations.  If you try to use AFs for general
>transformations, you're exactly right: you'll quickly discover that
>they don't do much for you.  They don't do nearly enough!  

They *are* about transformation. That is how they purport
to facilitate interchange. N connunicating
entities agree to use an architectural DTD. Parsing with
respect to the architectural
DTD *is* a transformation from each of the N source DTDs
to the architectural DTD.

(Note that I am not using your term "meta-DTD" as I don't
believe it is appropriate for what AFs do).

>Now here's the real point.  Without AFs, there are only two choices,
>in all cases where all the players in an industry must communicate
>freely with each other:
>(1) Everybody has to use the same DTD or Schema (which ain't gonna
>    happen for reasons too obvious to mention here), or
>(2) Everybody uses different DTDs, and, for N DTDs, there must be
>    roughly N-squared transformation specifications to convert between
>    them.

There are three choices - not two:-

 (3) Agree an interchange DTD. For N DTDs, there are N transformations
     to the interchange DTD. This is *exactly* what AFs do where
     "interchange DTD" == "architectural DTD".

     However, by choosing to use AFs for this, you (IMHO severly)
     limit the degree of mapping between the source DTD and the
     interchange DTD.

I am a big fan of interchange DTDs. My experience,FWIW, is that
the differences between DTDs that need to be mapped to an
interchange DTD are almost always such that the transformation
to the interchange DTD cannot be expressed with AFs.

>AFs provide a paradigm in which, *precisely because AF transformations
>are so bloody limited in their transformational power*, everybody gets
>to control their own DTDs, and, at the same time, everybody's messages
>are interpretable and validatable as industry-standard messages.

I don't follow this. You seem to be saying that the limimitations on
AF transformation power somehow helps. Please explain.



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