The UML metamodel
A special feature of the UML specification is that it defines UML using a subset of UML. It uses Class diagrams to describe which UML element types exist, what properties they have, and how they are related to one another. The entirety of what is shown in these Class diagrams is referred to as the UML metamodel. Apart from the Class diagrams, the UML specification also includes numerous OCL expressions, which describe consistency conditions on the one hand and the implementation of complex queries on the other. These are also part of the UML metamodel but will not be discussed further in this UML introduction. In this metamodel, the UML element types are defined in the form of metaclasses. The various properties of the UML element types are described using attributes and associations. Abstract metaclasses define properties that are shared by several different UML element types and whose metaclasses inherit from these abstract metaclasses.
The architecture for description and implementation of metamodels is described in the MOF (Meta Object Facility) standard published by the OMG. An ARIS-specific MOF implementation called OMF (Object Modeling Framework) represents a central component of the architecture of ARIS UML Designer.
Basic knowledge of the UML meta model is useful to understand UML and is essential for modeling UML profiles (see UML profiles ).
A short extract of the UML metamodel is introduced below, which defines those UML elements that are used in the Class diagram from Figure 1. The metamodel diagrams shown largely correspond to the relevant originals from the UML 2.5 specification. However, in some cases they have been adapted to the needs of this section by omitting individual metaclasses that are not dealt with further here, or by adding content from other diagrams in the UML specification.
The section headings used below correspond to the headings of the sections from the UML specification that contain the corresponding diagrams, so that you can easily find them in the UML specification to extend your knowledge of the subject.