EXPRESS Ed.2 SEDS

[Ed Barkmeyer]

All,

Tom Kramer and Peter Denno brought the following to my attention:

Problem Statement:

In Part 11.2:2003, clause 9.2.5.2, after the normative text, the following NOTE 
is to be found:

"NOTE The phrase ONEOF(a,b,c) reads in natural language as 'an instance shall 
consist of one and only one of the entity data types a,b,c.'"

The NOTE does not correctly convey the intent of the normative text.

Proposed change:

Either: The words "one and only one" should be replaced by "at most one"
or: the words "shall consist of one and only one" should be replaced by
"shall not consist of more than one".  (I prefer the latter.)

Discussion:

The NOTE is incorrect in that it causes the following mis-interpretation:

ENTITY xyz; ... END_ENTITY;
ENTITY a SUBTYPE OF (xyz); ... END_ENTITY;
ENTITY b SUBTYPE OF (xyz); ... END_ENTITY;
ENTITY c SUBTYPE OF (xyz); ... END_ENTITY;
ENTITY q SUBTYPE OF (xyz); ... END_ENTITY;
SUBTYPE_CONSTRAINT XYZ_not_both_A_B FOR (xyz);
  sc1: ONEOF(a,b,c);
END_SUBTYPE_CONSTRAINT;

Consider the instance (external mapping):
  #123 = (D(...) Q(...));

#123 is a valid instance of d and q according to the normative text,
but it is an invalid instance according to the NOTE, since it does not consist 
of any of the data types a,b,c.

-Ed

-- 
Edward J. Barkmeyer                       Email: edbark at nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
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