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From: wahl@shodha.dec.com (David Wahl)
Newsgroups: comp.object
Subject: re: Question on PDES, IGES, and EXPRESS.
Message-ID: <794@shodha.dec.com>
Date: 2 Mar 90 16:51:39 GMT
Organization: Digital Equipment Corp. - Colorado Springs, CO.
Lines: 55

For those who may not be familiar with the names, PDES, IGES and
Express are various languages and meta-languages for representing data
models for data exchange between CAD and CAM tools.  They are defined
as part of ANSI and ISO (the name in ISO for PDES is STEP) activities
to move toward standards for electronic data exchange for CAD/CAM.

I don't have an opinion as to whether the comp.object audience cares
about these things.  Express is based on a lot of ER and OO ideas; the
other stuff is mostly graphics for mechanical CAD/CAM.  The closest
thing to an appropriate newsgroup might be comp.graphics, although the
time might be right to consider a comp.cim (computer-integrated
manufacturing) newsgroup.  

If comp.objectians object to a discussion of something which is only
casually objective I'll not object to moving this discussion to email.

In 1007 siping@cerc.wvu.wvnet.edu asks:
>(1). Is IGES represented in EXPRESS?

Express is the meta-language for describing entities which are used in
a PDES application program.  PDES subsumes IGES, but some things are
different. 

>(2). From my limited references, I assume EXPRESS can represent
>     entity data type and instances of a generic entity. Can
>     some one verify this for me? How to make an instance of an
>     entity?
>(3). Does PDES represent instances of the generic entities?

There is no provision for direct instantiation of Express entities.
The intent is for Express to be a specification language for [logical,
conceptual, fuzzy, still-kinda-muddled] CAD/CAM entities which is
the basis for detail design into concrete PDES schemata.

>(4). Has anyone tried to make a translation from EXPRESS to a
>     schema language, such as KEE or Knowledge Craft?

Translation of Express or any ER based language into another really rich
schema language is easy.  The hard part is using the specification to
transform one existing un-objective, less semantically rich CAD format
to another where no common exchange protocol currently exists.

Regards,
Dave Wahl
===================================================================
Digital Equipment Corporation
Database Systems Research (CXN/2)
1175 Chapel Hills Drive
Colorado Springs, CO 80920-2080

Tel 719-260-2758
Email: wahl%cookie.dec.com@decwrl.dec.com
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% The opinions expressed are my own, not Digital's.               %
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