EXPRESS11 — The INDETERMINATE instance cannot have a type

It is not possible in most implementations to specify the object-identifier for an object. In clause 10.2, Figure 10.1, “INDETERMINATE” is used as the object-identifier for an Object/Instance that has no distinguishing properties. The only modeled property of the Indeterminate metaclass (inherited from Instance) is the type(s) that the object instantiates. Clause 10.2.7 says the EXPRESS INDETERMINATE instance is not an instance of any type, but it can be treated as an instance of the required data type of the Expression, if any. That is the semantic rule, but it cannot possibly work in an implementation if the INDETERMINATE value is unique: It assumes that each use of it is a different Instance with different values for ‘of-type’. It must be a requirement that the ‘of-type’ property is always empty. In that way, the INDETERMINATE object can be identified as such. And, using MOF reflection, it is the only object that identifies its Class as “Indeterminate”.

The INDETERMINATE value is deleted by the resolution to Issue 18815, precisely because it has no modeled properties. It should be a property of the Indeterminate class that SELF.of-type is always empty.
At the same time, the existing ‘is-singleton’ constraint should be rephrased in MOF terms.