The Esterel synchronous programming language and its mathematical semantics

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Rewriting Logic Semantics of a Plan Execution Language

The Plan Execution Interchange Language (PLEXIL) is a synchronous language developed by NASA to support autonomous spacecraft operations. In this paper, we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance logical engine. The rewriting logic semantics is by itself a formal interpreter of the language and can be used as a semantic benchmark for the implementation of PLEXIL executives. The implementation in Maude has the additional benefit of making available to PLEXIL designers and developers all the formal analysis and verification tools provided by Maude. The formalization of the PLEXIL semantics in rewriting logic poses an interesting challenge due to the synchronous nature of the language and the prioritized rules defining its semantics. To overcome this difficulty, we propose a general procedure for simulating synchronous set relations in rewriting logic that is sound and, for deterministic relations, complete. We also report on two issues at the design level of the original PLEXIL semantics that were identified with the help of the executable specification in Maude

On convergence-sensitive bisimulation and the embedding of CCS in timed CCS

We propose a notion of convergence-sensitive bisimulation that is built just over the notions of (internal) reduction and of (static) context. In the framework of timed CCS, we characterise this notion of `contextual' bisimulation via the usual labelled transition system. We also remark that it provides a suitable semantic framework for a fully abstract embedding of untimed processes into timed ones. Finally, we show that the notion can be refined to include sensitivity to divergence

Towards Coq-verified Esterel Semantics and Compiling

This paper focuses on semantics of the Esterel synchronous programming language. In particular, in addition to the usual behavioral (CBS) and state (CSS) semantics, it introduces a novel microstep semantics which does not need the Can potential function. Formal proofs in Coq of the equivalence between the CBS and CSS semantics and of the refinement between the CSS and microstep semantics are also provided

A sequentially constructive circuit semantics for Esterel

Static Single Assignment (SSA) is an established concept that facilitates various program optimizations. However, it is typically restricted to sequential programming. We present an approach that extends SSA for concurrent, reactive programming, specifically for the synchronous language Esterel. This extended SSA transformation expands the class of programs that can be compiled by existing Esterel compilers without causality problems. It also offers a new, efficient solution for the well-studied signal reincarnation problem. Finally, our approach rules out speculation/backtracking, unlike the recently proposed sequentially constructive model of computation

Process Algebras

Process Algebras are mathematically rigorous languages with well defined semantics that permit describing and verifying properties of concurrent communicating systems. They can be seen as models of processes, regarded as agents that act and interact continuously with other similar agents and with their common environment. The agents may be real-world objects (even people), or they may be artifacts, embodied perhaps in computer hardware or software systems. Many different approaches (operational, denotational, algebraic) are taken for describing the meaning of processes. However, the operational approach is the reference one. By relying on the so called Structural Operational Semantics (SOS), labelled transition systems are built and composed by using the different operators of the many different process algebras. Behavioral equivalences are used to abstract from unwanted details and identify those systems that react similarly to external experiments