A formal approach for software maintenance

Software systems evolve because user requirements change over time. Maintaining software systems is a challenge, especially when the old behavior has to be preserved while new functionality is added. In this paper, we extend the transformational model to the maintenance phase and call it extended transformational model. Using this extended transformational model, we develop an approach to maintain SDL (Specification and Description Language) specifications. This approach consists of enriching, in three phases, SDL specifications with new behaviors specified with another formal language MSC (Message Sequence Charts). The approach is based on a formally defined enrichment relation that must hold between the old and the new SDL specifications.