Abstract. We introduce a novel approach to the smart execution of scenario-based models of reactive systems, such as those resulting from the multi-modal inter-object language of live sequence charts (LSCs). Our approach finds multiple execution paths from a given state of the system, and allows the user to interactively traverse them. The method is based on translating the problem of finding a superstep of execution into a problem in the AI planning domain, and issuing a known planning algorithm, which we have had to modify and strengthen for our purposes. 1

Abstract. We investigate the power of play-out, the execution mechanism associated with scenario-based programming, which was defined as the operational semantics of live sequence charts (LSC). We compare some of the play-out strategies and mechanisms suggested in the literature, and discuss their strengths and limitations. Specifically, we define a simple infinite hierarchy of LSC programs, and use it to show that smart play-out, the lookahead version of play-out guided by model-checking, is strictly weaker than full synthesis from LSC. This paper is dedicated to Prof. Willem de Roever, friend and colleague, with admiration and respect for his scientific achievements, his impact on the community, and his boundless energy. 1

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