ModelBus is a middleware system that offers the interoperability between CASE tools for supporting software development according to MDA. This interoperability allows tools to share services and models, by using an RPC mechanism. ModelBus adopts the call-by-copy-restore semantic, as it is very close to local call semantic and is flexible as regards tools’ heterogeneous model representations. In this work, we extend this semantic to enable only specific model fragments to be passed as parameters, instead of complete models. The advantages are 1) improving the performance because passing only model fragments requires less data processing and 2) enhancing access control to models because the service’s modification can be restricted to the specific model fragment that is specified as parameters. The implementation of this work is available as the Eclipse project Model Driven Development integration (MDDi).