Final technical agreement for EXPRESS 2

[Pascal Huau]

Dear all


Peter wrote:
> o I recall that within STEP USE (or is it REFERENCE?) can (could?) only be
used in IRs and REFERENCE (or is it USE) can (could?) only be used in APs.
This was justified by "If you look at an EXPRESS model you can tell if it is
an AP or an IR according to its use of USE or REFERENCE". Certainly at one
time USE/REFERENCE were artifacts of the STEP documentation architecture and
did not reflect any  information modeling first/second class distinction .

PH: although I was not there at the begining of STEP, my interpretation of
the use of Reference for IRs and USE for AP AIMs is different.
REFERENCE FROM is used for IRs as they were thought as interrelated entity
types libraries.
USE FROM is used in AP AIM short forms, to show how the final long-form
schema is built aggregating express constructs from various sources.


> o If existence dependence is modeled via global rules, what is the impact
on the size and clarity of the model? For example, what would the AP203 long
form look like with the proposed dependent rules?
> o Will anyone implement such rules? (Does anyone implement any global
rule?)

PH: Existence dependence rules (or rule of subtype exclusiveness) directly
come from the STEP foundation principle of a translation of information
requirements (ARM) into an express schema (AIM) using standard resources.
Any time an entity attribute of the ARM is translated with an IR entity, an
dependent_instantiable_xxx rule is needed in the long form schema.
Not having these rules or equivalent constructs would make that the AIM is
not a correct translation of the ARM.


Regards,
Pascal Huau
98, avenue Albert 1er
92500 Rueil-Malmaison
FRANCE
Tel/Fax: 33 (0)147084963

----- Original Message -----
From: "Wilson, Peter R" <peter.r.wilson at boeing.com>
To: <Phil.Spiby at Eurostep.com>; <wg11 at steptools.com>
Cc: "Wilson, Peter R" <peter.r.wilson at boeing.com>
Sent: Friday, April 18, 2003 6:20 PM
Subject: RE: Final technical agreement sought for EXPRESS 2


>     Please consider the following regarding the dependent rule.
>
> o I recall that within STEP USE (or is it REFERENCE?) can (could?) only be
used in IRs and REFERENCE (or is it USE) can (could?) only be used in APs.
This was justified by "If you look at an EXPRESS model you can tell if it is
an AP or an IR according to its use of USE or REFERENCE". Certainly at one
time USE/REFERENCE were artifacts of the STEP documentation architecture and
did not reflect any  information modeling first/second class distinction .
>
> o Existence dependence is modeled in EXPRESS via multi-schema models and
USE/REFERENCE. The STEP architecture (i.e., a single long form) deliberately
threw away that distinction.
>
> o If existence dependence is modeled via global rules, what is the impact
on the size and clarity of the model? For example, what would the AP203 long
form look like with the proposed dependent rules?
>
> o Will anyone implement such rules? (Does anyone implement any global
rule?)
>
>     Personally, as a general principle I think that global rules should be
avoided wherever possible and only used as a last resort when all other
model constraint methods have been exhausted. I am concerned about Phil's
suggestion that a SELECT type would have to be introduced into the long form
to enable the dependent rules; it's getting complicated and hints at
artificiality.
>
>     I would like to see the dependent rules eliminated from the short to
long algorithm, especially as I think that the USE/REFERENCE in STEP is an
architectural artifact and does not represent real modeling requirements. If
that is not acceptable then I am strongly of the opinion that the rules must
be optional and not required.
>
> Peter W.
>
> Dr Peter R. Wilson
> Boeing Commercial Airplanes
> PO Box 3707, MS 2R-97, Seattle, WA 98124-2207
> Tel: (206) 544-0589, Fax: (206) 544-5889
> Email: peter.r.wilson at boeing.com