Abstract. The diagnosis of``intermittent'' faults in dynamic systems modeled as discrete event systems is considered. In many systems, faulty behavior often occurs intermittently, with fault events followed by corresponding``reset'' events for these faults, followed by new occurrences of fault events, and so forth. Since these events are usually unobservable, it is necessary to develop diagnostic methodologies for intermittent faults. Prior methodologies for detection and isolation of permanent faults are no longer adequate in the context of intermittent faults, since they do not account explicitly for the dynamic behavior of these faults. This paper addresses this issue by: (i) proposing a modeling methodology for discrete event systems with intermittent faults; (ii) introducing new notions of diagnosability associated with fault and reset events; and (iii) developing necessary and suf®cient conditions, in terms of the system model and the set of observable events, for these notions of diagnosability. The de®nitions of diagnosability are complementary and capture desired objectives regarding the detection and identi®cation of faults, resets, and the current system status (namely, is the fault present or absent). The associated necessary and suf®cient conditions are based upon the technique of`d iagnosers'' introduced in earlier work, albeit the structure of the diagnosers needs to be enhanced to capture the dynamic nature of faults in the system model. The diagnosability conditions are veri®able in polynomial time in the number of states of the diagnosers.

The diagnosis of unobservable faults in large and complex discrete event systems modeled by parallel composition of automata is considered. A modular approach is developed for diagnosing such systems. The notion of modular diagnosability is introduced and the corresponding necessary and sufficient conditions to ensure it are presented. The verification of modular diagnosability is performed by a new algorithm that incrementally exploits the modular structure of the system to save on computational effort. The correctness of the algorithm is proved. Online diagnosis of modularly diagnosable systems is achieved using only local diagnosers.

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Le concept d’éco-conception, né dans la grande entreprise, peut-il être transposé aux entreprises artisanales ? Le développement d’outils logiciels d’analyse environnementale (de type cycle de vie, bilan énergétique ou empreinte écologique) a démocratisé l’accès aux données environnementales, qui sont désormais à la portée des petites entreprises. Mais celles-ci ne font-elles pas déjà de l’éco-conception sans le savoir, ainsi que le laisse penser une étude menée dans le Nord – Pas de Calais ?