Specifying features of an evolving software system

Software development is increasingly concerned with maintaining and extending existing software systems to meet the evolving user requirements. Many of these systems are feature-rich and are developed incrementally. As structures of existing software systems-in addition to the user requirements-influence the specifications, specifying these systems poses unique challenges. This paper reports on our experience of applying an engineering approach to specifying an evolving feature-rich television software system. In this approach, features are specified modularly by first fitting their problems to known problem patterns, and then analyzing typical concerns-meaning the potential causes of errors-associated with those patterns. In cases where the existing design poses difficulties when fitting problems to patterns, we transform its structure using known design mechanisms so that the problems fit the patterns. After deriving specifications of individual features, possible interactions between features are detected, before declaratively specifying resolutions to undesired interactions. As the concerns of features and their composition are addressed separately, the specifications derived are modular, thus, providing rich treaceability to their requirements. As well as discussing how features may be specified using natural language, we also show how their descriptions may be formalized using a form of temporal logic called the Event Calculus, and prove their correctness using an off-the-shelf tool. Copyright (C) 2009 John Wiley & Sons, Ltd.