8.3.4 Constraints

   The well-formedness rules of the metaclass, except for multiplicity and ordering constraints that are defined in the diagram at the beginning of the package section, are defined as a (possibly empty) set of invariants for the metaclass, which must be satisfied by all instances of that metaclass for the model to be meaningful. The rules thus specify constraints over attributes and associations defined in the metamodel. Most invariants are defined by OCL expressions together with an informal explanation of the expression, but in some cases invariants are expressed by other means (in exceptional cases with natural language). The statement ‘No additional constraints’ means that all well-formedness rules are expressed in the superclasses together with the multiplicity and type information expressed in the diagrams.