A Semantics of Simultaneous Events (SSE) for State-Based Formal Specification

Simple state-based models use events corresponding to sets of prestate, poststate pairs of system states, and solve the frame problem --- i.e. knowing what else has changed, given that an event has occurred --- by assuming non-concurrent events that uniquely determine the poststate. However, such events are `overspecified' and thus not reusable in other models. This paper describes a more flexible approach to state-based concurrency and the frame problem, in which events --- loosely specified in semantic terms --- may occur simultaneously and can be reused in different contexts without `promotion'.