Necessity of Part 25 change supporting ONEOF?

[Bernd G. Wenzel]

Lothar,

David's comment must be read in the context of Part 25, which
should be useful outside of STEP. Therefore David is right.

You're addressing a different issue. The usage of EXPRESS by
other parts of the STEP standard is questionable for many
reasons. That's why it is sometimes nearly impossible to use
off-the-shelf EXPRESS tools for performant STEP implementations.
Some tools have STEP switches to control their execution. I agree
with you, that this should be fixed, but I don't know, who is
going to pay for it.

:-) Bernd

----- Original Message -----
From: Lothar Klein <lothar.klein at lksoft.com>
To: David Price <dmprice at us.ibm.com>
Cc: <wg10 at steptools.com>; <xmlsc4 at nist.gov>; <wg11 at smiling.net>
Sent: Friday, March 02, 2001 9:47 PM
Subject: Re: Necessity of Part 25 change supporting ONEOF?


>
> David,
>
> The problem here is more a political.
> Do we just want to map EXPRESS with UML or do
> we want to make STEP data models available in UML?
> In the first case your proposals sounds good.
> In the second case however it makes little sense since
> the ONEOF and ANDOR stuff is more or less totally broken
> in STEP data models. In actual APs and IRs there exist
> soooo many valid but wrong ANDOR combinations that it
> makes little sense to map this to UML.
>
> My proposal is to
> - make EXPRESS rich enough to model "weak ONEOFs"
> - go through all IRs and APs and use this new feature
> - and then to map STEP with UML
>
> Am I the only one who thinks we should fix STEP?
>
> Lothar
>
>
>
> David Price wrote:
> >
> > Folks,
> >
> > I've thought a little more about this and believe that to
allow the correct
> > EXPRESS SUPERTYPE semantics to be somehow represented in UML
we should do
> > the following:
> >
> > 1 - If there is no SUPERTYPE constraint, specify the UML
overlapping
> > constraint.
> > 2 - If there is exactly one ONEOF that covers all subtypes of
an entity
> > type, specify the UML disjoint contraint.
> > 3 - In all other cases where any SUPERTYPE constraint is
specified, specify
> > the UML overlapping constraint.
> >
> > 1 and 2 should be clear. I'm proposing 3 because it allows
for the overlaps
> > that do occur in EXPRESS to be represented in the UML model.
It does also
> > allow more combinations in the UML than are legal in the
EXPRESS but we
> > can't allow fewer combinations - which is what happens if you
specify
> > disjoint (or nothing since disjoint is the default). We'll
have to assume
> > that when people create data, the AP or a usage guide they
are using to
> > explain what's legal will result in correct data generation.
Perhaps as UML
> > constraints are harmonized with EXPRESS constraints we can
add more to the
> > mappings in the future.
> >
> > Anyone disagree with this approach? Anyone agree?
> > Thanks,
> > David
> >
> > IBM Corporation
> > 5300 International Blvd.
> > N. Charleston, SC 29418, USA
> > dmprice at us.ibm.com
> > Phone : +1 (843) 760-4341   Fax : +1 (843) 760-3349
> > Oooo.
> > (UNC)
> >  ) /
> > (*/
> >
> > David Price/Bethesda/IBM at IBMUS@steptools.com on 02/16/2001
12:57:02 PM
> >
> > Sent by:  owner-wg10 at steptools.com
> >
> > To:   wg10 at steptools.com, xmlsc4 at nist.gov, wg11 at smiling.net
> > cc:
> > Subject:  Re: Necessity of Part 25 change supporting ONEOF?
> >
> > Folks,
> >
> > If we were going to do anything about this I'd propose
something like the
> > following (or as I said, do nothing):
> >
> > PROPOSAL - For each EXPRESS entity data type visible in the
context of the
> > mapping that has subtypes visible in the context of the
mapping and within
> > which no SUPERTYPE constraint is specified, a UML
"overlapping" constraint
> > shall appear in the UDS. For each EXPRESS entity data type
that is a
> > subtype of the EXPRESS entity data type within which no
SUPERTYPE
> > constraint is specified, include the UML Generalization
representing that
> > EXPRESS subtype relationship in the UML "overlapping"
constraint created
> > for the EXPRESS supertype.
> >
> > Thanks,
> > David
> >
> > IBM Corporation
> > 5300 International Blvd.
> > N. Charleston, SC 29418, USA
> > dmprice at us.ibm.com
> > Phone : +1 (843) 760-4341   Fax : +1 (843) 760-3349
> > Oooo.
> > (UNC)
> >  ) /
> > (*/
> >
> > David Price/Bethesda/IBM at IBMUS@steptools.com on 02/16/2001
11:43:53 AM
> >
> > Sent by:  owner-wg10 at steptools.com
> >
> > To:   wg10 at steptools.com, xmlsc4 at nist.gov, wg11 at smiling.net
> > cc:
> > Subject:  Necessity of Part 25 change supporting ONEOF?
> >
> > Part 25/EXPRESS/UML Folks,
> >
> > At the Charleston ISO meeting I was given the following
change to make to
> > Part  25:
> >
> > "5 - Make EXPRESS ONEOF an explicit UML disjoint constraint
between
> > subclasses of a
> > common UML Class representing an EXPRESS entity that is a
supertype when
> > specified
> > in the EXPRESS supertype constraint."
> >
> > After reviewing the UML 1.3 spec further I think this change
is not
> > necessary. In fact, if we do anything we need to add
"overlapping" in the
> > case where no SUPERTYPE constraint is specified.
> >
> > Here's what UML 1.3 says about : Generalization
> >
> > A generalization is a taxonomic relationship between a more
general element
> > and a more specific element. The more specific element is
fully consistent
> > with the more general element (it has all of its properties,
members, and
> > relationships) and may contain additional information. In the
metamodel, a
> > Generalization is a directed inheritance relationship,
uniting a
> > GeneralizableElement with a more general GeneralizableElement
in a
> > hierarchy. Generalization is a subtyping relationship (i.e.,
an Instance of
> > the more general GeneralizableElement may be substituted by
an Instance of
> > the more specific  GeneralizableElement). See Inheritance for
the
> > consequences of Generalization relationships.
> >
> > Here are two of the Standard Constraints that can be applied.
Note that
> > "disjoint" (i.e. ONEOF) is the default!
> >
> > disjoint
> >
> > Specifies a constraint applied to a set of generalizations,
indicating that
> > instance of the parent may be an instance of no more than one
of the
> > given children within the set of generalizations. This is the
default
> > semantics of generalization.
> >
> > overlapping
> >
> > Specifies a constraint applied to a set of generalizations,
indicating that
> > an instance of one child may be simultaneously an instance of
another
> > child in the set (but there is no guarantee that such an
instance will
> > actually exist).
> >
> > Opinions on what do to? I think either 1) do nothing or 2)
add overlapping
> > if no supertype constraint at all, but let's not try and
> > figure out the complete set of permutations.
> >
> > Thanks,
> > David
> >
> > IBM Corporation
> > 5300 International Blvd.
> > N. Charleston, SC 29418, USA
> > dmprice at us.ibm.com
> > Phone : +1 (843) 760-4341   Fax : +1 (843) 760-3349
> > Oooo.
> > (UNC)
> >  ) /
> > (*/
>
> --
> // Lothar Klein, LKSoftWare GmbH
> // Steinweg 1, 36093 Kuenzell, Germany
> // Tel: +49 661 933933-0, Fax: -2
> // Email: lothar.klein at lksoft.com
> // URL: http://www.lksoft.com