[wg11] Part 28 comment JP-5 meets EXPRESS Ed.2

[Ed Barkmeyer]

All,

With respect to JP-5, we decided in Groton (in the absence of Japanese 
or UK or Norway representatives) to let Part 28 v1 stand as an ISO TS, 
with the "parsed exchange of EXPRESS models" as specified in Annex C of 
that Edition.

Per the previous email, that probably does not meet the intent of JP-5.

But, since Part 28 v1 Annex C is a direct explosion of the Part 11:1994 
*grammar* into XML, there is another problem.  In Part 11:2004, that 
grammar has changed in a number of places, which causes the EXPRESS Ed2 
*parse* to be somewhat different from the EXPRESS v1 parse, even for an 
EXPRESS corpus that conforms to both grammars.  That makes the use of 
Part 28 v1 Annex C very difficult to explain!

Further, because of the EXPRESS Ed.2 introduction of ABSTRACT ENTITY and 
"generic attributes", EXTENSIBLE types, and attribute RENAME, most of 
these grammar changes affect the parse of entities, attributes and data 
types!  That means that the most important use of the v1 mapping is 
disaligned with the Part11 Ed2 grammar!  So in answer to David's 
question, this is a strong reason why not.

The P28v1 mapping applies only to an EXPRESS Ed1 schema, using the now 
"provisionally retained" EXPRESS Ed1 (and its grammar) to interpret the 
XML elements.

I don't see that SC4 can continue to support the Part 28 v1 mapping as 
relevant, particularly for the exchange of "module schemas".  And I 
don't believe that "use Part 28 v1 Annex C" is in any sense a 
satisfactory resolution of JP-5.

-Ed

P.S.  Sorry for the belated epiphany.  I had to say the word "parse" in 
the email to Tanaka-san, before I realized what the problem was.

P.P.S.  Note also that this is a strong argument for the meta-model 
concept hidden in the STEPmod representation.  EXPRESS v2 is 
semantically an upward-compatible extension of EXPRESS v1, and the 
language is also an upward-compatible extension.  But the *grammar*, as 
a set of production rules, is *not* an upward-compatible extension.  And 
because the Part 28 v1 mapping represents the production rules verbatim, 
it is now useless.  (For Josh's benefit, I would say that this is a 
doc-head thing -- a grammar is a corpus model, not a content model.)

-- 
Edward J. Barkmeyer                        Email: edbark at nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8264                Tel: +1 301-975-3528
Gaithersburg, MD 20899-8264                FAX: +1 301-975-4694

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