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The specification uses the Object Constraint Language (OCL), as defined in Chapter 6, “Object Constraint Language Specification?
of the UML 1.4 specification, for expressing well-formedness rules. The following conventions are used to promote readability:
• Self — which can be omitted as a reference to the metaclass defining the context of the invariant, has been kept for clarity.
• In expressions where a collection is iterated, an iterator is used for clarity, even when formally unnecessary. The type of the iterator is usually omitted, but included when it adds to understanding.
• The ‘collect’ operation is left implicit where this is practical.
• The context part of an OCL constraint is not included explicitly, as it is well defined in the section where the constraint appears.