A Semantics of Communicating Reactive Objects with Timing

Jozef Hooman and Mark van der Zwaag

Software Tools for Technology Transfer (STTT) Volume 8, Number 4, pages 97-112, 2006.


The aim of this work is to provide a formal foundation for the unambiguous description of real-time, reactive, embedded systems in UML. For this application domain, we define the meaning of basic class diagrams where the behavior of objects is described by state machines. These reactive objects may communicate by means of asynchronous signals and synchronous operation calls. The notion of a thread of control is captured by a so-called activity group, i.e., a set of objects which contains exactly one active object and where at most one object may be executing. Explicit timing is realized via local clocks and an urgency predicate on transitions. We define a formal semantics for this kernel language, list a number of questions that arose, and discuss the decisions taken. The resulting semantics has been defined in the typed logic of the interactive theorem prover PVS, thus enabling formal verification based on this semantics.

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