The design of a complex system warrants a compositional methodology, i.e., composing simple components to obtain a larger system that exhibits their collective behavior in a meaningful way. We propose an automaton-based paradigm for compositional design of such systems where an action is accompanied by one or more preferences. At run-time, these preferences provide a natural fallback mechanism for the component, while at design-time they can be used to reason about the behavior of the component in an uncertain physical world. Using structures that tell us how to compose preferences and actions, we can compose formal representations of individual components or agents to obtain a representation of the composed system. We extend Linear Temporal Logic with two unary connectives that reflect the compositional structure of the actions, and show how it can be used to diagnose undesired behavior by tracing the falsification of a specification back to one or more culpable components.
A general framework for fault ascription in concurrent systems based on is presented in @cite_30 @cite_25 . Formal definitions are given for failures in a given set of components to be necessary and or sufficient cause of a system violating a given property. Components are specified by sets of sets of events (analogous to actions) representing possible correct behaviors. A parallel (asynchronous) composition operation is defined on components, but there is no notion of composition of events or explicit interaction between components. A system is given by a global behavior (a set of event sets) together with a set of system component specifications. The global behavior, which must be provided separately, includes component events, but may also have other events, and may violate component specifications (hence the faulty components). In our approach, global behavior is obtained by component composition. Undesired behavior may be local to a component or emerge as the result of interactions.
@cite_30 @cite_25
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Fault diagnosis is becoming increasingly important and difficult with the growing pervasiveness and complexity of computer systems. We propose in this paper a general semantic framework for fault ascription, a precise form of fault diagnosis that relies on counterfactual analysis for identifying necessary and sufficient causes of faults in component-based systems. Our framework relies on configuration structures to handle concurrent systems, partial and distributed observations in a uniform way. It defines basic conditions for a counterfactual analysis of necessary and sufficient causes, and it presents a refined analysis that conforms to our basic conditions while avoiding various infelicities. This paper presents an approach for the specification and the verification of the correctness of fault tolerant system designs achieved by the application of fault tolerant techniques. The approach is based on process algebras, equivalence theory and temporal logic. The behaviour of the system in the absence of faults is formally specified and faults are assumed as random events which interfere with the system by modifying its behaviour. The fault tolerant technique is formalized by a context that specifies how replicas of the system cooperate to deal with faults. The system design is proved to behave correctly under a given fault hypothesis by proving the observational equivalence between the system design specification and the fault-free system specification. Additionally, model checking of a temporal logic formula which gives an abstract notion of correct behaviour can be applied to verify the correctness of the design. The opportunities given by the expression of the fault hypothesis using temporal logic are discussed. The actual usability of the approach in real case studies is supported by the availability of automatic tools for equivalence checking and for proving the temporal logic properties by model checking. We present a method for combined fault localization and correction for sequential systems. We assume that the specification is given in linear-time temporal logic and state the localization and correction problem as a game that is won if there is a correction that is valid for all possible inputs. For invariants, our method guarantees that a correction is found if one exists. The set of fault models we consider is very general: components can be replaced by arbitrary new functions. We compare our approach to model based diagnosis and show that it is more precise. We present experimental data that supports the applicability of our approach, obtained from a symbolic implementation of the algorithm in the Vis model checker. We give a denotational framework (a "meta model") within which certain properties of models of computation can be compared. It describes concurrent processes in general terms as sets of possible behaviors. A process is determinate if, given the constraints imposed by the inputs, there are exactly one or exactly zero behaviors. Compositions of processes are processes with behaviors in the intersection of the behaviors of the component processes. The interaction between processes is through signals, which are collections of events. Each event is a value-tag pair, where the tags can come from a partially ordered or totally ordered set. Timed models are where the set of tags is totally ordered. Synchronous events share the same tag, and synchronous signals contain events with the same set of tags. Synchronous processes have only synchronous signals as behaviors. Strict causality (in timed tag systems) and continuity (in untimed tag systems) ensure determinacy under certain technical conditions. The framework is used to compare certain essential features of various models of computation, including Kahn process networks, dataflow, sequential processes, concurrent sequential processes with rendezvous, Petri nets, and discrete-event systems.