Grid automata and supervisory control of dense real-time discrete event systems

We present a generalization of the classical supervisory control theory for discrete event systems to a setting of dense real-time systems modeled by Alur and Dill timed automata. The main problem involved is that in general the state space of a timed automaton is (uncountably) infinite. The solution is to reduce the dense time transition system to an appropriate finite discrete subautomaton, the grid automaton, which contains enough information to deal with the timed supervisory control problem (TSCP). The plant and the specifications region graphs are sampled for a granularity defined in a way that each state has an outgoing transition labeled with the same time amount. We redefine the controllability concept in the context of grid automata, and we provide necessary and sufficient solvability conditions under which the optimal solution to centralized supervisory control problems in timed discrete event systems under full observation can be obtained. The enhanced setting admits subsystem composition and the concept of forcible event. A simple example illustrates how the new method can be used to solve the TSCP.     

Experimenting with Feature Interaction Management in SIP Environment

This article reports architectural aspects of a solution for detecting and resolving feature interactions (FI) in SIP-based IP telephony architectures. The solution takes into account the special context of SIP that permits end user programmability, which means the possibility for end users to design their own tailored services and personalize them as much as they like. Programmability renders more frequent the so called multi-component FI situations, where the conflicting services reside in different network components. This type of FI is the more complicated one. The authors describe how the different components of the presented SIP architecture operate together in order to run services and avoid this type of interactions. A prototype of the solution has been developed.     

A Supervisory Control Method for Ensuring the Conformance of Real-Time Discrete Event Systems

In this article, we study the problem of controlling a plant described as a real-time discrete event system. The aimed objective is to ensure a conformance relation denoted tioco between the plant and the formal specification of the system, by means of a supervisor. We adopt a two-step approach. In Step 1, we express the problem into a non-real-time form, by using a transformation of timed automata (TA) into particular finite state automata called Set-Exp-Automata (SEA). The latter use two additional types of events, Set and Exp. And in Step 2, we propose a non-real-time control method suitable for SEA. We also propose a control architecture.     

A temporal approach for testing distributed systems

This paper deals with testing distributed software systems. In the past, two important problems have been determined for executing tests using a distributed test architecture: controllability and observability problems. A coordinated test method has subsequently been proposed to solve these two problems. In the present article: 1) we show that controllability and observability are indeed resolved if and only if the test system respects timing constraints, even when the system under test is non-real-time; 2) we determine these timing constraints; 3) we determine other timing constraints which optimize the duration of test execution; 4) we show that the communication medium used by the test system does not necessarily have to be FIFO; and 5) we show that the centralized test method can be considered just as a particular case of the proposed coordinated test method.     

<Emphasis Type="Italic">SetExp</Emphasis>: a method of transformation of timed automata into finite state automata

Real-time discrete event systems are discrete event systems with timing constraints, and can be modeled by timed automata. The latter are convenient for modeling real-time discrete event systems. However, due to their infinite state space, timed automata are not suitable for studying real-time discrete event systems. On the other hand, finite state automata, as the name suggests, are convenient for modeling and studying non-real time discrete event systems. To take into account the advantages of finite state automata, an approach for studying real-time discrete event systems is to transform, by abstraction, the timed automata modeling them into finite state automata which describe the same behaviors. Then, studies are performed on the finite state automata model by adapting methods designed for non real-time discrete event systems. In this paper, we present a method for transforming timed automata into special finite state automata called Set-Exp automata. The method, called SetExp, models the passing of time as real events in two types: Set events which correspond to resets with programming of clocks, and Exp events which correspond to the expiration of clocks. These events allow to express the timing constraints as events order constraints. SetExp limits the state space explosion problem in comparison to other transformation methods of timed automata, notably when the magnitude of the constants used to express the timing constraints are high. Moreover, SetExp is suitable, for example, in supervisory control and conformance testing of real-time discrete event systems.     

Multi-decision diagnosis: decentralized architectures cooperating for diagnosing the presence of faults in discrete event systems

This article deals with decentralized diagnosis, where a set of diagnosers cooperate for detecting faults in a discrete event system. We propose a new framework, called multi-decision diagnosis, whose basic principle consists in using several decentralized diagnosis architectures working in parallel. We first present a generic form of multi-decision diagnosis, where several decentralized diagnosis architectures work in parallel and combine their global decisions disjunctively or conjunctively. We then study in more detail the inference-based multi-decision diagnosis, that is, in the case where each of the decentralized architectures in parallel is based on the inference-based framework. We develop a method that checks if a given specification is diagnosable under the inference-based multi-decision architecture. We also show that with our method, the worst-case computational complexity for checking codiagnosability for our inference-based multi-decision architecture is in the same order of complexity as checking codiagnosability for the inference-based architecture designed by Kumar and Takai. In fact, multi-decision diagnosis is fundamentally undecidable and we have formulated a decidable variant of it. Multi-decision diagnosis is formally based on language decomposition, but it is worth noting that our objective is not to answer the existential question of language decomposition in the general case. Our objective is rather to propose a decentralized diagnosis architecture that generalizes the decidable existing ones.