UMLNIEM — NIEM-UML Issue: Constraint schema and other constraint/rule support

NIEM-UML does not currently support constraint schema, a NIEM feature needed by many practitioners. Constraint schema and other mechanisms for constraints and rules should be provided for in NIEM-UML.

As constraints and schema are essentially “unbounded”, specific features and their UML representation needed should be identified. This should include:

· Multiple subsets of the same class that may have different properties for different needs

· Subsets that constrain property types to subtypes that are not in the reference schema

· Changes in cardinality or aggregation

· Arbitrary OCL expressions

The profile should allow an information model to be marked as also generating one or more constraint mechanisms including constraint schema, OCL engines and schematron. However, only the mapping to constraint schema need be defined at this time. In providing for this capability the complexity for the modeler should be minimized – the constraints should be able to be expressed in the same package and elements as the NIEM schema types (e.g. subset and extension schema).

Suggested Resolution:
In the PIM Perspective, a subset <<InformationModel>> may override the type of a reference <<InformationModel>> Property. The overridden type must be a subtype of the reference <<InformationModel>> Property type. The transformation to the PSM Perspective results in a schema set which enforces the original reference <<InformationModel>> Property types, plus a constraint schema set which reflects the Property type overrides.
Resolution:
The suggested resolution is accepted. Clauses 7.6.1.2 and 7.6.1.3 are extended with descriptions of modeling subset type constraints in the PIM Perspective, and the mapping of those constraints to the PSM Perspective.