Existential live sequence charts revisited

Scenario-based specifications are a popular means for describing intended system behaviour. We aim to facilitate early analysis of system behaviour and the development of behaviour models in conjunction with scenarios. In this paper we define a novel scenario-based specification language with an existential semantics and that supports conditional specification of behaviour in the form of prechart and main chart. The language semantics is consistent with existing informal scenario-based and use-case based approaches to requirements engineering. The language provides a good fit with universal live sequence charts as standard existential live sequence charts do not adequately support conditional scenarios. In addition, we define a novel synthesis algorithm that, rather than building arbitrarily one of the many behaviour models that satisfy a scenario, constructs a modal transition system (MTS) which characterizes all behaviour models that conform to the scenario.