Synthesizing Modal Transition Systems from Triggered Scenarios

Abstract

Abstract-Synthesis of operational behaviour models from scenario-based specifications has been extensively studied. Focus has been mainly on either existential or universal interpretations. One noteworthy exception is Live Sequence Charts which provides expressive constructs for conditional universal scenarios and some limited support for non-conditional existential scenarios. In this paper we propose a scenario-based language that supports both existential and universal interpretations for conditional scenarios. Existing model synthesis techniques use traditional two-valued behaviour models, such as Labelled Transition Systems. These are not sufficiently expressive to accommodate specification languages with both existential and universal scenarios. We therefore shift the target of synthesis to Modal Transition Systems, an extension of Labelled Transition Systems that can distinguish between required, unknown and proscribed behaviour to capture the semantics of existential and universal scenarios. Modal Transition Systems support elaboration of behaviour models through refinement, which complements an incremental elicitation process suitable for specifying behaviour with scenario-based notations. The synthesis algorithm that we define constructs a Modal Transition System that uses refinement to characterise all the Labelled Transition Systems models that satisfy a mixed, conditional existential and universal scenario-based specification. We show how this combination of scenario language, synthesis and Modal Transition Systems supports behaviour model elaboration.

Distributing refinements of a system-level partial behavior model

“…Our work targets the widely used requirements notations: temporal properties [8], event invariants [2] and triggered scenarios [19]. Requirements specified in these notations can be mapped to an MTS that satisfies them [11], [19], [22].…”

“…We also provide an argument for the framework's correctness with respect to the intent behind the requirement driving the process. We have applied our framework on a case study found in prior related literature [19], [21]. The case study results suggest that our framework helps to correctly refine the MTSs, to avoid inconsistencies, and to analyze the system's behavior.…”

“…The specification notations used early in a system's life cycle, such as FLTL properties [8], triggered scenarios [19], and event invariants [2], are intuitive and inherently partial, focusing on narrow aspects of the system's behavior. For example, a scenario describes a single required sequence of interactions between the system's components, whereas a safety property proscribes some system behavior as illegal.…”

“…To this end, researchers have proposed synthesizing a system's partial behavior model [6], [7], [11], [12], [18], [19], [22], represented using an FSA-based formalism such as modal transition systems (MTS) [14], from the system requirements. A synthesized MTS can be used for requirements inconsistency detection [6], [11], [17], validation and verification [4], as well as elicitation of new, currently unspecified requirements [1], [19], [22]. Intuitively, in an MTS, which distinguishes between required, maybe, and prohibited state transitions, a scenario is captured using required transitions, while MTS's maybe transitions should not violate the safety properties nor the invariants.…”

“…In particular, these notations treat a system as a monolithic entity whose behavior can then be represented with a single system-level MTS [2], [8], [10], [19], [22]. By contrast, software systems typically consist of independent, interacting components whose behavior should be described in separate component MTSs [11].…”