Benoît Fraikin

A standard ontology for smart spaces

This paper presents a universal ontology for smart environments aiming to overcome the limitations of the existing ontologies. We enrich our ontology by adding new environmental aspects such as the referentiality and environmental change, that can be used to describe domains as well as applications. We show through a case study how our ontology is used and integrated in a self-organising middleware for smart environments.

Extending statecharts with process algebra operators

This paper describes an adaptation of statecharts to take advantage of process algebra operators like those found in CSP and EB3. The resulting notation is called algebraic state transition diagrams (ASTDs). The process algebra operators considered include sequence, iteration, parallel composition, and quantified synchronization. Quantification is one of the salient features of ASTDs, because it provides a powerful mechanism to precisely and explicitly define cardinalities in a dynamic model. The formal semantics of ASTDs is expressed using the operational style typically used in process algebras. The target application domain is the specification and implementation of information systems.

State-based versus event-based specifications for information systems: a comparison of B and eb 3

This paper compares two formal methods, B and eb3, for specifying information systems. These two methods are chosen as examples of the state-based paradigm and the event-based paradigm, respectively. The paper considers four viewpoints: functional behavior expression, validation, verification, and evolution. Issues in expressing event ordering constraints, data integrity constraints, and modularity are thereby considered. A simple case study is used to illustrate the comparison, namely, a library management system. Two equivalent specifications are presented using each method. The paper concludes that B and eb3 are complementary. The former is better at expressing complex ordering and static data integrity constraints, whereas the latter provides a simpler, modular, explicit representation of dynamic constraints that are closer to the user’s point of view, while providing loosely coupled definitions of data attributes. The generality of these results from the state-based paradigm and the event-based paradigm perspective are discussed.

A SAT-based approach for the construction of reusable control system components

This paper shows how to take advantage of a SAT-solving approach in the development of safety control software systems for manufacturing plants. In particular, it demonstrates how to construct reusable components which are assembled after instantiation to derive controllers of modular production systems. An experiment has been conducted with Alloy not only to verify properties required by a control theory for complex systems organized hierarchically, but also to synthesize two major parts of a component: observer and supervisor. The former defines its interface while guaranteeing nonblocking hierarchical control. The latter ensures the satisfaction of constraints imposed on its behavior and on the interactions among its subcomponents during system operation. As long as the size of component interfaces is small, SAT-solvers appear useful to build correct reusable components because the formal models that engineers manipulate and analyze are very close to the abstract models of the mathematical theory.

Supervisory control theory with Alloy

Scientific literature reveals that the symbolic representation techniques underlying some formal methods are useful in verifying properties or synthesizing parts of large discrete event systems. They involve, however, encoding complex schemata and fine-tuning heuristic parameters in order to translate specific problems into efficient BDD- or SAT-based representations. This approach may be too costly when the main goal is to explore a theory, use simulation to understand its underlying concepts and computation procedures, and conduct experiments by applying them to problems in different fields as the theory evolves over time. To achieve this goal, this paper investigates the use of Alloy in modeling and prototyping varying fragments of the supervisory control theory, including the verification of nontrivial properties such as controllability, normality and observational equivalence. It also shows how to apply abstract models for synthesizing optimal supervisors and reports on an experiment suggesting that Alloy can be used to synthesize supervisors for concrete systems using hierarchical decomposition.

Modeling the supervisory control theory with alloy

Scientific literature reveals that symbolic representation techniques behind some formal methods are attractive to synthesize parts or verify properties of large discrete event systems. They involve, however, complex encoding schemata and fine tuning heuristic parameters in order to translate specific problems into efficient BDD or SAT-based representations. This approach may be too costly when the main goal is to explore a theory, understand by simulation its underlying concepts and computation procedures, and conduct experiments by applying them to small problems. Based on previous work with Alloy on the synthesis of observers and nonblocking supervisors of a system organized hierarchically with a flat state space estimated to 1031 states, this paper investigates more deeply issues raised with its use in the modeling and prototyping of the supervisory control theory, including the application of models to practical problems. This study was conducted in a broader context than just hierarchical control since it embraces various variants of this theory.

Efficient symbolic computation of process expressions

This paper describes three optimization techniques for the eb^3 process algebra. The optimizations are expressed in a new deterministic operational semantics which is shown to be trace-equivalent to a traditional non-deterministic operational semantics. Internal action transitions are eliminated by an efficient preruntime analysis of the structure of a process expression. Execution environments are used to optimize variable instantiation using lazy evaluation. Non-determinism is eliminated by returning a choice between possible transitions. This new operational semantics is implemented in the eb^3pai process algebra interpreter to support the eb^3 method. The goal of this method is to automate the development of information systems using, among other mechanisms, efficient symbolic computation of process expressions.

Efficient symbolic execution of large quantifications in a process algebra

This paper describes three optimization techniques for a process algebra interpreter called EB3PAI. This interpreter supports the EB3 method, which was developed for the purpose of automating the development of information systems using efficient symbolic execution of abstract specifications. The proposed optimizations allow an interpreter to execute actions on a quantified choice in constant time and on a quantified parallel composition in logarithmic time with respect to the number of entities in a quantified entity type. This time complexity is comparable to that of programmer-derived implementation of process expressions and significantly better than the time complexity of common process algebra simulators, which execute quantifications by computing their expansion into binary expressions.

Automatic Generation of Error Messages for the Symbolic Execution of EB3 Process Expressions

This paper describes an algorithm to automatically generate error messages for events refused by a process expression. It can be used in the context of an information system specified with the EB3 method. In this method, a process expression is used to describe the valid traces of events that the information system must accept. If a user submits an event which is rejected by this process expression, our algorithm produces an error message explaining why the event has been rejected; it also suggests which event should be submitted in order to correct the error.

A reachability graph construction technique for supervisor synthesis with parameters

This paper describes a technique to construct reachability graphs from replicated structures. This new technique can be combined with an off-line synthesis algorithm in order to automatically generate nonblocking supervisors in closed form. Replicated structures arise from the modeling of similar processes and similar cases, which are components of parameterized discrete event systems and workflow processes, respectively. The analysis and control of such systems require a state space exploration. The proposed approach weakens the state explosion problem by using symbols and expressions instead of numerical values in markings, which makes it possible to obtain supervisors with explicit conditions in their control actions.