  In this paper, we present an approach to define the semantics for
object-oriented modeling languages. One important property of this semantics is
to support underspecified and incomplete models. To this end, semantics is
given as predicates over elements of the semantic domain. This domain is called
the system model which is a general declarative characterization of object
systems. The system model is very detailed since it captures various relevant
structural, behavioral, and interaction aspects. This allows us to re-use the
system model as a domain for various kinds of object-oriented modeling
languages. As a major consequence the integration of language semantics is
straight-forward. The whole approach is supported by tools that do not
constrain the semantics definition's expressiveness and flexibility while
making it machinecheckable.
