Maintenance and evolution of software systems require to modify or exchange system components. In many cases, we would like the new component versions to be backward compatible to the old ones, at least for the use in the given context. Whereas on the program level formal techniques to precisely define and verify backward compatibility are under development, the situation on the system level is less mature. A system component C has not only communication interfaces to other system components, but also to human users or the environment of the system. In such scenarios, compatibility checking of different versions of C needs more than program analysis: 1. The behavior of the users are not part of the program, but needs to be considered for the overall system behavior. 2. If the user interaction in the new version is different from the old one, the notion of compatibility needs clarification. 3. Analyzing the user interface code makes checking technically difficult. We suggest to use behavioral software models for compatibility checking. In our approach, the underlying system, the old and new component, and the nonde-terministic behavior of the environment are modeled with the concurrent object-oriented behavioral modeling language ABS. Abstracting from implementation details, the checking becomes simpler than on the program level.
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