With the development of complex systems based on SDL, performance issues often play a major role. However, this is neither reflected by the SDL methodology nor by the specification techniques suggested by the methodology, namely SDL and MSC. To remedy this problem, we propose Performance Message Sequence Chart (PMSC). PMSC represents an extension of MSC-96 to include performance aspects into the language. The extensions allow for the formal specification of various performance aspects, e.g. performance requirements, resource requirements and the specification of the available resources. In order to support the use of tools based on MSC-96, the language extensions are embedded in comments of the original MSC-96 language. PMSC allows for the co-specification of functional and performance aspects. This joint specification of functional and performance aspects eases the task of software engineers. It saves effort otherwise needed to maintain two different models. In addition, the co-specification based on MSC, rather than on SDL, supports the early evaluation of the performance of the system.
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