Specifying Interacting Components with Coordinated Concurrent Scenarios

We introduce a visual notation for local specification of concurrent components based on message sequence charts (MSCs). Each component is a finite-state machine whose actions are MSCs that specify its local view of the overall communication in the system. These local MSCs are composed into coherent global scenarios using a separately specified set of transactions. Intuitively, each MSC represents a phase of interaction. We introduce a mechanism to overlap phases that allows complex interactions to be specified without obscuring the logical structure of the constituent scenarios. Our notation combines the global view available in models such as high-level message sequence charts (HMSCs) with the local, asynchronous structure captured by message-passing automata (MPA). In fact, both HMSCs and MPAs can be captured as special cases of our formalism. In this paper we focus on the syntax and formal semantics of our notation, with examples that illustrate why this approach is more natural for capturing real-life specifications. We also describe an approach to use automated tools to analyze systems specified using our notation.