So you say you want a revolution

[Bernd G. Wenzel]

Dave,

what you're suggesting would work, but I wouldn't like to do it
this way. Your wording at least suggests, that it is not your
favourite solution either.

If I understand Alan correctly, he's complaining about the
representation of a partial entity instance in an exchange file,
if external mapping is used.

Under all circumstances EXPRESS-2 makes sure, that we know for
every legal entity instance the type for each and every attribute
(although it may be a SELECT type). It is IMHO not the job of P21
to specify, what should be done with instances, which are
incorrect according to P11. So we are safe.

When we now come to the external mapping, I know, that some, but
not all, implementors do not like it, because they have to parse
the whole instance, before they know what the damned thing is
(validation) or maps to (processing). This is the situation with
EXPRESS-1 already. So it is not impacted by the capabilities of
EXPRESS-2.

If my understanding of Alan's argument is correct, the complexity
was introduced when we allowed attribute redeclaration. We have
not added an additional quality here.

:-) Bernd

----- Original Message -----
From: <david-price at btclick.com>
To: <wg11 at steptools.com>
Sent: Friday, October 26, 2001 1:32 PM
Subject: RE: Re: So you say you want a revolution


>
> Alan,
> Your reply presupposes how P21 with E2 would work. One could
also think of any attribute that was not instantiable as simply a
pattern/template/constraint for modelers that does not affect
data. So, P21 could say to ignore any attribute that does not
have a type that is instantiable. Then these attributes, all with
the same name, would simply appear in the subtypes, not in the
ABSTRACT ENTITY. I'm not necessarily suggesting that I think this
is the best approach. I'm just suggesting that there is more than
one way to address this issue.
>
> Cheers,
> David
>
>
> Original Message:
> -----------------
> From: Alan R Williams alanrw at cs.man.ac.uk
> Date: Fri, 26 Oct 2001 11:44:13 +0100 (BST)
> To: wg11 at steptools.com
> Subject: Re: So you say you want a revolution
>
>
>
> > Date: Thu, 25 Oct 2001 17:05:09 -0400
> > From: Ed Barkmeyer <edbark at cme.nist.gov>
> > X-Sender: "Ed Barkmeyer" <edbark at mailhost.cme.nist.gov>
> > X-Accept-Language: en,pdf
> > To: Martin Hardwick <hardwick at steptools.com>
> > CC: edbark at nist.gov, wg11 at steptools.com
> > Subject: Re: So you say you want a revolution
> >
> [mega snip]
> > None of this is true.  The only entity types that can
actually appear directly
> in an exchange are the leaf types of the
> > inheritance tree, and in those types, every inherited generic
attribute must
> be re-declared to a specific Express:1994 data
> > type.
>
> Isn't that only sort-of true?  In a Part 21 file, you could use
the
> external form for complex entity instances.  In the partial for
the
> abstract entity declaration, the attribute value needed would
be generic,
> wouldn't it?
>
> > So when you look at an instantiable exchange schema, all of
those generic
> attributes disappear!
>
> [mega snip]
> > -Ed
> >
> > P.S. I want a revolution, but I would start by defining a
meta-model that does
> not have a one-to-one map into either Express or
> > UML.  I'm not likely to find many pragmatists flocking to my
red banner. So
> since we have a working kludge, let's just keep
> > kludging it, until the real revolution buries us. ;-)
> >
> > --
> > Edward J. Barkmeyer                       Email:
edbark at nist.gov
> > National Institute of Standards & Technology
> > Manufacturing Systems Integration Division
> > 100 Bureau Drive, Mail Stop 8260          Tel: +1
301-975-3528
> > Gaithersburg, MD 20899-8260               FAX: +1
301-975-4482
> >
> > "The opinions expressed above do not reflect consensus of
NIST,
> > and have not been reviewed by any Government authority."
>
> Alan
>
> Alan Williams, Room IT301, Department of Computer Science,
> University of Manchester, Oxford Road, Manchester, M13 9PL,
U.K.
> Tel: +44 161 275 6270      Fax: +44 161 275 6280
>
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