Specifying Logical System Interfaces

System interfaces identify the sets of services, data, and flows into and out of a system. By logical interfaces, we mean abstract interfaces that specify the content and precision of the flows but not their physical realization. For example, a system interface to a radar might include a message herezaRadarTrack(r: RadarTrack) as a SysML event carrying a radar track as a parameter without specifying what communication means will be used, let alone the bit-mapped structure of the realizing 1553 Bus message. Nevertheless, the specification of the interface allows us to consider the set of services requested of the system by actors, the set of services needed by the system from actors, and the physical and information flow across the system boundary.

The initial set of interfaces is a natural outcome of use case analysis. Each use case characterizes a set of interactions of the system with a group of actors for a similar purpose. These interactions...