EXPRESS11 — EXPRESS MM MOF model does not include the UML InstanceSpecifications in the specification

The EXPRESS MM specification defines three Packages – BuiltInTypes, BuiltInConstants, and GenericTypes – that contain UML InstanceSpecifications. It also contains the Instance INDETERMINATE in the Instances package. These InstanceSpecifications represent predefined elements of the EXPRESS language that are instances of more general classes (of types and values) defined in the language. Because MOF does not support InstanceSpecification, the v1.0 MOF model does not contain any representation of these model elements. Standard representation of these model elements is critical to interoperable interchange of EXPRESS models. Some MOF-compatible representation of these model elements must be included in the specification and/or the normative artifacts.

The InstanceSpecifications are maintained in the (informative) UML model and in the text. The MOF model is accompanied by a “module” in the EXPRESS (M1) XMI form. For simplicity, the EXPRESSElements module combines all the UML packages. This is described in a new section (16) of the text. To properly construct the module, it is necessary to add the formal properties (slots) to the InstanceSpecifications.
It was noted in creating the EXPRESS modules that, although ISO 10303-11 refers to the elements in the BuiltInConstants module as “constants”, they are really just reserved words that are treated as Literals when they appear in expressions. Accordingly, the BuiltInConstants package is renamed BuiltInConstants and moved to the Expressions package, and the module is named accordingly. This has the advantage of allowing them to be formally included in a Scope as ‘Scope.expression’.
Note that moving the package does not affect conformance to the Expressions compliance point, because Expressions imports Instances. Technically it reduces requirements for the Instances compliance point, but Instances package support for the values that these Literals refer to is still required.
In a similar way, the INDETERMINATE object is already represented as a separate Expression (Primary) subclass: IndeterminateRef, and serves no purpose. It is deleted from the model.
Because Issue 19037 adds an attribute to the GenericType instances, the corresponding text changes are incorporated into the revised text below.