Dr. Achiya Elyasaf

In scenario-based models of reactive systems complex specifications are divided into artifacts corresponding to separate aspects of overall system behavior, as they may appear, e.g., in a robot’s requirements document or user specifications. The advantages of scenario-based development include intuitiveness and clarity, the ability to execute or simulate specifications of early prototypes and of final systems, and the ability to verify the specification for early detection of conflicts, omissions, and errors. In this position paper we discuss two issues that emerge when applying scenario-based development in complex cases: (a) simple scenarios become unwieldy when subjected to a growing number of conditions, exceptions and refinements, and (b) it is hard to understand and maintain a large ‘flat’ specification, consisting of an unorganized list of independently-specified scenarios, simple as they may individually be. We address these issues by basing certain facets of scenario design on context, an increasingly popular foundational consideration in software engineering. We first show how one can incorporate context into the graphical language of live sequence charts (LSC) using existing LSC idioms. We then outline two other possibilities: (i) enriching the LSC language, or (ii) embedding LSCs within hierarchical state machines, namely, statecharts. We believe that this research can contribute to the broader goals of developing complex and powerful reactive systems in intuitive and robust ways.