Josef Hofer

• For the development of the Extremely Large Telescope (ELT), the European Southern Observatory (ESO) uses state machines to model life cycles and basic behaviour of control software components. To provide certain degrees of freedom, the component life cycles need to be customisable but in order to remain compatible, they must also conform to specific standard behaviour. Clearly, these two goals are competing. High customisation causes difficulties in maintenance and may also lead to incompatible solutions. The introduction of strict compatibility requirements on the other hand may increase maintainability but it also makes the system less flexible. To avoid spending a significant portion of the Assembly, Integration and Verification (AIV) phase in integration hell, it is of high importance to find the right balance between customisability and compatibility early enough. To address this problem, this thesis examines different variability realisation mechanisms with respect to their applicability for the behavioural customisation of state machine models. Based on this information, a novel approach is presented that combines a set of variability realisation mechanisms and thereby enables open and stepwise customisation, systematic reuse and separation of concerns. Concretely, the method enhances a framework approach with model manipulation capabilities and mixin composition while also supporting conditional compilation and conditional execution. Moreover, the thesis demonstrates that compatibility can be ensured by combining constructive and analytical methods, namely feature orientation and conformance testing. Finally, feasibility and soundness of the elaborated solution concept are demonstrated using a proof of concept implementation that has already been applied to a real-world project in scope of the ELT program.