OMG Unified Modeling Language Specification

Syntax The abstract syntax is presented in a UML class diagram showing the metaclasses defining theconstructs and their relationships. The diagram also presents some of the well-formedness rules,mainly the multiplicity requirements of the relationships, and whether or not the instances of aparticular sub-construct must be ordered. Finally, a short informal description in naturallanguage describing each construct is supplied. The first paragraph of each of these descriptionsis a general presentation of the construct which sets the context, while the following paragraphsgive the informal definition of the metaclass specifying the construct in UML. For eachmetaclass, its attributes are enumerated together with a short explanation. Furthermore, theopposite role names of associations connected to the metaclass are also listed in the same way. Well-Formedness Rules The static semantics of UML metaclasses, except for multiplicity and ordering constraints, aredefined as a set of invariants of an instance of the metaclass. (Note that a metaclass is notrequired to have any invariants.) These invariants have to be satisfied for the construct to bemeaningful. The rules thus specify constraints over attributes and associations defined in themetamodel. Each invariant is defined by an OCL expression together with an informalexplanation of the expression. In many cases, additional operations on the metaclasses areneeded for the OCL expressions. These are then defined in a separate subsection after the well-formedness rules for the construct, using the same approach as the abstract syntax: an informalexplanation followed by the OCL expression defining the operation. The statement ‘No extra well-formedness rules’ means that all current static semantics areexpressed in the superclasses together with the multiplicity and type information expressed inthe diagrams. 2. Although a comprehension of the UML’s four-layer metamodel architecture and itsunderlying meta-metamodel is helpful, it is not essential to understand the UML semantics.3. In order to understand the description of the UML semantics, you must understand someUML semantics. UML V1.3June 19992-9