The Model Driven Engineering approach has had an important impact on the methods used for the conception of systems. However, some important difficult points remain in this domain. In this paper, we focus on problems related to the heterogeneity of the computation models (and there fore of the modeling techniques) used for the different aspects of a system and to the validation and the execution of a model. We present here a language for describing computation models, coupled with a generic execution platform where different computation models as well as their composition can be interpreted. Our goal is to be able to describe precisely the semantics of the computation models underlying Domain Specific Languages, and to allow the interpretation of these models with in our platform. This provides for a non ambiguous definition of the be havior of heterogeneous models of a system, which is essentialf or validation, simulationand code generation.