[wg11] RE: [step-os] Part 28 comment JP-5 meets EXPRESS Ed.2

[Ed Barkmeyer]

David Price wrote:

>  I suggest falling back to one of my earlier suggestions:
> 
> Include the STEPMod DTD as an informative annex in Part 28 E2 - or run it
> through an XML tool that translates DTDs to XML Schema and include that XML
> Schema instead. 

I agree with this, in the latter version.  Part 28 v2 should contain an 
XML Schema description of the exchange form, not a DTD.  Also I think 
you want a human expert to review the automatic translation and improve 
the resulting XML schema with the proper use of XML data types.

I agree that the Annex should be informative.

I agree that no text is required, *so long as* there is <documentation> 
in the XML schema that relates the tags to the Part 11 terms.

> Below is the extract of that DTD for entity data types and global rule so
> you can see its approach :
> 
> <!ELEMENT entity (description?, explicit*, derived*, inverse*, unique*,
> where*, graphic.element?)>
> <!ATTLIST entity
> 	name NMTOKEN #REQUIRED
> 	abstract.entity (YES | NO) "NO"
> 	abstract.supertype (YES | NO) "NO"
> 	supertypes NMTOKENS #IMPLIED
> 	super.expression CDATA #IMPLIED

Asides:

(1) ABSTRACT SUPERTYPE is a proper subtype of ABSTRACT ENTITY:  Abstract 
entities *may* have "generic attributes"; abstract supertypes are not 
permitted to.  That is the *only* difference.  An abstract entity that 
has no generic attributes is not semantically distinguishable from an 
abstract supertype.  We should actually deprecate the use of ABSTRACT 
SUPERTYPE.

(2) supertype expression *is* deprecated in EXPRESS Ed2, in favor of 
SUBTYPE_CONSTRAINT, which can carry all of the same information and 
more.  Every valid supertype expression is a valid SUBTYPE_CONSTRAINT, 
i.e.  ENTITY x <supertype expression> maps 1-to-1 to:
   SUBTYPE_CONSTRAINT FOR (x);
    <supertype expression>;
   END_SUBTYPE_CONSTRAINT;

I would recommend that you think about making that transform, since 
SUBTYPE_CONSTRAINTs for the same (x) can be *added* in other modules and 
APs that use the ENTITY type, and that gives you a uniform 
representation of the constraint set for a given (x).

-Ed

-- 
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
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