A semantics of communicating reactive objects with timing

Abstract

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, which is 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, based on the run-to-completion paradigm. We show that this combination of communication primitives and execution mechanism gives rise to a large number of questions and discuss the decisions taken in the proposed semantics. The resulting semantics has been defined in the typed logic of the interactive theorem prover PVS.

Modeling and Validating Distributed Embedded Real-Time Systems with VDM++

“…However, object creation can be added easily, see e.g. [55]. Threads can be created dynamically, e.g., to deal with asynchronous operation calls.…”

“…In [83] a labeled transition system has been defined using the algebraic specification language CASL, whereas [ 55] uses the specification language of the theorem prover PVS to formulate the semantics. Note that UML 2.0 adopts the run-to-completion semantics, which means that new signals or operation calls can only be accepted by an object if it cannot do any other local action, i.e., it can only proceed by accepting a signal or call.…”

Supporting UML-based development of embedded systems by formal techniques

“…To be able to use the PVS system for the verification of UML models, we have represented the semantics of the OMEGA kernel model in PVS [23]. The general idea is that an execution of the UML model is represented by a run (i.e., an execution trace) which is a sequence of the form c 0 → c 1 → c 2 → c 3 → · · · where the c i are configurations, representing a snapshot of the system during execution and each pair of successive configurations represents a step of a state machine of one of the objects or a time step.…”

“…Similarly, threads of control have been added in a modular way. More details can be found in [23], which clarifies a number of semantic questions and decisions, e.g., concerning the passing of control and the dispatching of signal events.…”

Validation of UML Models via a Mapping to Communicating Extended Timed Automata

“…Effort is put into: finding the right concepts (e.g. communication mechanisms between objects, concurrency model, timing specification features, see [12]), defining them formally (a formalization in PVS is available [23]) and implementing and testing these concepts in tools.…”