Ma Michel Reniers

Syntax and consistent equation semantics of hybrid Chi

Abstract The hybrid χ (Chi) formalism integrates concepts from dynamics and control theory with concepts from computer science, in particular from process algebra and hybrid automata. It integrates ease of modeling with a straightforward, structured operational semantics. Its ‘consistent equation semantics’ enforces state changes to be consistent with delay predicates, that combine the invariant and flow clauses of hybrid automata. Ease of modeling is ensured by means of the following concepts: (1) different classes of variables: discrete and continuous, of subclass jumping or non-jumping, and algebraic; (2) strong time determinism of alternative composition in combination with delayable guards; (3) integration of urgent and non-urgent actions; (4) differential algebraic equations as a process term as in mathematics; (5) steady-state initialization; and 6) several user-friendly syntactic extensions. Furthermore, the χ formalism incorporates several concepts for complex system specification: (1) process terms for scoping that integrate abstraction, local variables, local channels and local recursion definitions; (2) process definition and instantiation that enable process re-use, encapsulation, hierarchical and/or modular composition of processes; and (3) different interaction mechanisms: handshake synchronization and synchronous communication that allow interaction between processes without sharing variables, and shared variables that enable modular composition of continuous-time or hybrid processes. The syntax and semantics are illustrated using several examples.

An Algebraic Semantics of Basic Message Sequence Charts

Message Sequence Charts are a widely used technique for the visualization of the communications between system components. We present a formal semantics of Basic Message Sequence Charts, exploiting techniques from process algebra. This semantics is based on the semantics of the full language as being proposed for standardization in the International Telecommunication Union.

High-level Message Sequence Charts

Publisher Summary This chapter includes a definition of the semantics of the sublanguage high-level message sequence charts (HMSCs) of MSC96, based on the recommended process algebra semantics of MSC92. The chapter discusses the use of HMSC by studying the well-known Alternating Bit Protocol (ABP) from different views. This case study motivates to extend MSC96 with gates on HMSC nodes. HMSC is mainly used for vertical decomposition and for displaying alternative scenarios. The chapter presents two views of the ABP: an overall description expressing the control flow and an instance-oriented description. The HMSC specification of the ABP benefits from the possibility to consider complete message sequence charts (MSCs) as a node in an HMSC specification rather than as a reference. The possibility to switch among different views within the same language fits very well with the variety of uses of the MSC language. A thorough study on the relation among these different views is an important step toward the (semi-) automatic derivation of Specification and Description Language (SDL) code from MSC scenarios.

A Rule Format for Associativity

We propose a rule format that guarantees associativity of binary operators with respect to all notions of behavioral equivalence that are defined in terms of (im)possibility of transitions, e.g., the notions below strong bisimilarity in van Glabbeeks spectrum. The initial format is a subset of the De Simone format. We show that all trivial generalizations of our format are bound for failure. We further extend the format in a few directions and illustrate its application to several formalisms in the literature. A subset of the format is studied to obtain associativity with respect to graph isomorphism.

Maximal Synthesis for Hennessy-Milner Logic

This article concerns the maximal synthesis for Hennessy-Milner Logic on Kripke structures with labeled transitions. We formally define, and prove the validity of, a theoretical framework that modifies a Kripke model to the least possible extent in order to satisfy a given HML formula. Applications of this work can be found in the field of controller synthesis and supervisory control for discrete-event systems. Synthesis is realized technically by first projecting the given Kripke model onto a bisimulation-equivalent partial tree representation, thereby unfolding up to the depth of the synthesized formula. Operational rules then define the required adaptations upon this structure in order to achieve validity of the synthesized formula. Synthesis might result in multiple valid adaptations, which are all related to the original model via simulation. Each simulant of the original Kripke model, which satisfies the synthesized formula, is also related to one of the synthesis results via simulation. This indicates maximality, or maximal permissiveness, in the context of supervisory control. In addition to the formal construction of synthesis as presented in this article, we present it in algorithmic form and analyze its computational complexity. Computer-verified proofs for two important theorems in this article have been created using the Coq proof assistant.

Concrete Syntax and Semantics of the Compositional Interchange Format for Hybrid Systems

Abstract The compositional interchange format for hybrid systems is syntactically and semantically defined in terms of an interchange automaton in an abstract format, allowing among others differential algebraic equations, variables that can be internal or external, operators for parallel composition, action hiding, variable hiding and urgent actions, synchronization by means of shared labels, and communication by means of shared variables and CSP channels. A concrete format is defined for modeling. Its semantics is defined in terms of a mapping to the abstract format. The concrete format adds inputs, outputs and open and closed scopes to enable modular and hierarchical specifications. The concrete format is illustrated by means of a bottle filling line example.

Formal Semantics of Hybrid Chi

The verification formalism / modeling and simulation language hybrid Chi is defined. The semantics of hybrid Chi is formally specified using Structured Operational Semantics (SOS) and a number of associated functions. The χ syntax and semantics can also deal with local scoping of variables and/or channels, implicit differential algebraic equations, such as higher index systems, and they are very well suited for specification of pure discrete event systems.

A hierarchy of communication models for message sequence charts

In a Message Sequence Chart (MSC) the dynamical behaviour of a number of cooperating entities is depicted. An MSC defines a partial order on the communication events between these entities. This order determines the physical architecture needed for implementing the specified behaviour, such as a FIFO buffer between each of the entities. In a systematic way, we define 50 communication models for MSC and we define what it means for an MSC to be implementable by such a model Some of these models turn out to be equivalent, in the sense that they implement the same class of MSCs. After analysing the notion of implementability, only ten classes remain, for which we develop a hierarchy. We also develop algorithms to check whether a given MSC belongs to such a class.

Orthogonal extensions in structural operational semantics

In this paper, we give novel and more liberal notions of operational and equational conservativity for language extensions. We motivate these notions by showing their practical application in existing formalisms. Based on our notions, we formulate and prove meta-theorems that establish conservative extensions for languages defined using Structural Operational Semantics (SOS).

Using Aspect-GAMMA in the design of embedded systems

This paper proposes a design framework that takes advantage of the aspect-orientation paradigm. The proposed framework is based on the multi-set transformation language called GAMMA, used for the functional aspect, together with a set of modelling notations for other aspects of system design, namely coordination, timing and distribution.