On the Formal Interpretation of SysML Blocks Using a Safety Critical Case Study

Abstract

The Systems Modeling Language (SysML) is a semiformal, visual modelling language used in the specification and design of systems. In this paper, we describe how Communicating Sequential Processes (CSP) and its associated refinement checker, Failures Divergences Refinement (FDR), can be used in conjunction with SysML in a formal top-down approach to systems engineering. Typically, a system is composed from constituent systems or components using the concept of blocks. SysML allows two alternative interpretations with regards to the behaviour of the resulting composition. By making use of a process-algebraic formalism we are able to explore these interpretations more rigorously. A case study is used throughout to illuminate the concepts in an informal manner.

On a Process Algebraic Representation of Sequence Diagrams

“…Consider making use of sequence diagrams to check the validity of communicating state machines, as described by the present authors in [12] and [13]. Activities are considered in [21]. Using our model for sequence diagrams, we would be able to make use of events (like a state machine sending an asynchronous message) that correspond to interaction occurrences on the sequence diagram.…”

On the formal interpretation and behavioural consistency checking of SysML blocks

“…We now give consideration to a case study, which we will use to illustrate our contribution. The case study, reprised from [13], is used as a means to evaluate and illuminate the contribution of this paper. We study a single component -a robotic arm -of a fully fledged case study that is well known within the formal methods community.…”

“…In every case, the internal channel is used to receive events using the event passing mechanism. Signal events 13 are sent using the channel with the same name as the target block, similar to the approach taken for state machines 14 . we then have…”

“…In this paper we aim to demonstrate a comprehensive, integrated semantics considering both behavioural constructs. The case study presented in [13] is employed to illuminate and validate the contribution of this paper.…”

“…As an example, the action outputting the forward direction in Extend 13. As examples, see BDMotorOn in Extend for a send signal event and OnPD in Retract for a receive signal event 14.…”