Database Reference
In-Depth Information
Figure 2: Type inheritance hierarchy
semantic of the UML specialization — and is handled by the meta-interpreter, types and
instances are supported by the modeling engine, and their primary goal is to support model
reuse independently of the meta-model.
CONSTRAINT MANAGEMENT
One can consider the UML class diagram-based meta-model as syntax specifi cations.
It determines what concepts are used in the modeling language and specifi es relations and
attributes. It does not say much about what constitutes a correct model. We use the Object
Constraint Language (OCL) for the specifi cation of the static semantics of the modeling
language. Constraints are attached to the meta-models specifying well-formedness rules.
In addition to the OCL expression, a GME constraint has a priority attached to it speci-
fying the action the built-in constraint manager should take upon its violation. The highest
priority results in an error message and the abortion of the current transaction. Lower priority
violations only cause warning messages.
Constraints can be attached to editing events specifying when they must be checked.
For example, the “on connect” event should be specifi ed for a constraint that restricts the
kind or number of connections a given model can be attached to. Furthermore, all constraints
can be checked on-demand at any time.
Certain pieces of information captured in the meta-model cannot be compiled directly
into the paradigm confi guration because of the limitations of that format. In such cases,
such as the multiplicity information of containment, membership and connection cardinality
defi nitions, the meta-interpreter automatically generates OCL constraints.
