Re: Agenda item: XSD and DTD for CPP/CPA

[Martin W Sachs <mwsachs@us.ibm.com>]

Jamie,

You raise a good point about Schema and there is no easy answer.  The world
is moving towards Schema.  My biggest problem is that people are starting
to use schema snippets instead of instance document snippets as
illustrations.  That's got 80% noise level which interferes with my
comprehension.  It of course does allow the document writer to skip writing
all that English prose that fully specifies the elements and attributes in
the instance document but at the cost of forcing the reader to root through
the 400 pages of Schema specification to understand the requirements.

Philosophy aside, we have to balance the following against allowing people
to continue using DTDs:

   Sticking with things that can be expressed properly in the DTD gives up
   a lot of the benefits of Schema such as its richer data typing which
   means that the parser and provide the user with more information about
   violations of the instance document spec.

   A requirement to be able to generate a valid DTD from the Schema may
   sacrifice precision in in the Schema.  An example in the CPP-CPA spec is
   the ds:signature element.  That should have a cardinality of 0 to 3 in
   the CPA. However in the  DTD, I can't say "0 to 3".  I have to use a
   cardinality of maxOccurs("unbounded") in the Schema, which translates to
   a cardinality of * in the DTD.  I could perhaps say "ds:signature+,
   ds:signature+, ds:signature+" in the DTD, but I am not sure that any
   tool would generate that from maxOccurs("3").

So for version 1.0, the team (as, I think, did all ebXML teams) chose to
use a schema from which a valid DTD can be generated.  Now that Schema has
reached Recommendation status, this decision should be revisited.

Regards,
Marty


*************************************************************************************

Martin W. Sachs
IBM T. J. Watson Research Center
P. O. B. 704
Yorktown Hts, NY 10598
914-784-7287;  IBM tie line 863-7287
Notes address:  Martin W Sachs/Watson/IBM
Internet address:  mwsachs @ us.ibm.com
*************************************************************************************



James Bryce Clark <jamie.clark@mmiec.com> on 07/20/2001 02:19:56 PM

To:   ebxml-cppa@lists.oasis-open.org
cc:   Tony Weida <TonyW@EDIFECS.COM>
Subject:  Re: Agenda item: XSD and DTD for CPP/CPA



At 09:22 AM 7/20/01, Tony Weida wrote:
>Since XML Schema is now a formal W3C Recommendation, I propose that we
>consider dropping the DTD from the next major version of our spec.
>
>Tony

Just a preliminary reaction -- Isn't there a substantial non-behemoth user,
and would-be-adopter, base with a substantial legacy dependency DTDs?  You
might not want to bail on those people right away.    In spite of the
superiority and inevitability of schema, I'm not sure the upgrade path
looks easy to them.

Jamie


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