Using formal methods to create automatic code generation systems is one of the goals of Knowledge Based Software Engineering (KBSE) groups. The research of the Air Force Institute of Technology KBSE group has focused on the utilization of formal languages to represent domain model knowledge within this process. The code generation process centers around correctness preserving transformations that convert domain models from their analysis representations through design to the resulting implementation code. The diversity of the software systems that can be developed in this manner is limited only by the availability of suitable domain models. Therefore it should be possible to combine existing domain models when no single model is able to completely satisfy the requirements by itself. This work proposes a methodology that can be used to integrate domain models represented by formal languages. The integration ensures that the correctness of each input model is maintained while adding the desired functionality to the integrated model. Further, because of the inherent knowledge captured in the domain models, automated tool support can be developed to assist the application engineer in this process.