Precise UML Semantics Through Formal Metamodeling

We present an object-oriented metamodeling methodology based on a formal metalanguage suited for the deenition of the semantics of the UML but also for the deenition of other languages. This methodology allows for the description of all relevant aspects of the entities of the metamodel. We are particularly interested in the description of dynamic semantics, because it has been neglected in common metamodeling approaches. The dynamic semantics is important for understanding the concepts provided by the UML (e.g. dynamic behavior of statecharts, or lifetime dependency of composite aggregation). We provide a dichotomy for the classiication of metaentities into intensional and extensional entities. Using our approach, the metamodel level as well as the model level are described. Two kinds of instantiation relations are identiied: inter-level instantiation and intra-level instantiation. The examination of behavior of intensional as well as extensional enities within a single approach may lead to an integration of process aspects of software engineering with the used modeling techniques. 1 Metamodels A metamodel is a model for the information that can be expressed during (software) modeling. Basically, a metamodel is a model of models. It consists of entities deening the model elements and therefore the modeling language. The main purpose of a metamodel is to relate these model elements. Diierent levels of abstractions can be identiied in software modeling. Between each level there exists an instantiation relationship, e. g. a concept of a level is an instance of a concept of its upper level. Usually, a four-level approach (i.e. Ode95]) is used: Data and Process Level: This level is the lowest level. The entities on this level are run-time objects, i.e. instances of classes and processes running on a concrete system. Model Level: The model level is an abstraction to the data and process level. On this level, we have diierent models describing the underlying physical system. Metamodel Level: The metamodel level describes the concepts which are used in the model level. Meta-Metamodel Level: This level deenes the language in which the metamodel is described. The UML metamodel is also based on a four-level approach. Its metalanguage consists of UML class diagrams deening the metaentities, and of the Object Constraint Language OCL97] used for the description of well-formedness constraints between the metaentities. 1 2 Structuring the Metamodel An important contribution of our approach is the distinction between intensional and extensional entities in one abstraction level. Intensional entities have a counterpart …