Sebti Mouelhi

CoSyMA: a tool for controller synthesis using multi-scale abstractions

We introduce CoSyMA, a tool for automatic controller synthesis for incrementally stable switched systems based on multi-scale discrete abstractions. The tool accepts a description of a switched system represented by a set of differential equations and the sampling parameters used to define an approximation of the state-space on which discrete abstractions are computed. The tool generates a controller - if it exists - for the system that enforces a given safety or time-bounded reachability specification. We illustrate by examples the synthesized controllers and the significant performance gains during their computation.

Safety Controller Synthesis for Incrementally Stable Switched Systems Using Multiscale Symbolic Models

We propose an approach to the synthesis of safety controllers for a class of switched systems, based on the use of multiscale symbolic models that describe transitions of various durations and whose sets of states are given by a sequence of embedded lattices approximating the state-space, the finer lattices being accessible only by transitions of shorter duration. We prove that these multiscale symbolic models are approximately bisimilar to the original switched system provided it enjoys an incremental stability property attested by the existence of a common Lyapunov function or of multiple Lyapunov functions with a minimal dwell-time. Then, for specifications given by a safety automaton, we present a controller synthesis algorithm that exploits the specificities of multiscale symbolic models. We formalize the notion of maximal lazy safety controller which gives priority to transitions of longer durations; the shorter transitions and thus the finer scales of the symbolic model are effectively explored only when safety cannot be ensured at the coarser level and fast switching is needed. We propose a synthesis algorithm where symbolic models can be computed on the fly, this allows us to keep the number of symbolic states as low as possible. We provide computational evidence that shows drastic improvements of the complexity of controller synthesis using multiscale symbolic models instead of uniform ones.

Refinement of Interface Automata Strengthened by Action Semantics

Interface automata are light-weight models that capture the temporal interface behavior of software components. They have the ability to model both the input requirements and the output behavior of a component. They support the compatibility check between interface models to ensure a correct interaction between components and they adopt an alternating simulation approach to design refinement. In this paper, we extend our previous works on checking interface automata interoperability by adapting their alternating refinement relation to the action semantics. We show the relation between pre and post-conditions of transitions in the abstract version of an interface and their corresponding ones in its concrete version. We illustrate our extensions by a case study of the CyCab car component-based system.

Adapting Component Behaviours Using Interface Automata

One of the principal goal of Component-Based Software Engineering (CBSE) is to allow the reuse of components in diverse situations without affecting their codes. To reach this goal, it is necessary to propose approaches to adapt a component with its environment when behavioural mismatches occur during their interactions. In this paper, we present a formal approach based on interface automata to adapt components in order to eliminate possible behavioural mismatches, and then insure more flexible interoperability between components.

An I/O Automata-based Approach to Verify Component Compatibility: Application to the CyCab Car

An interesting formal approach to specify component interfaces is interface automata based approach, which is proposed by L. Alfaro and T. Henzinger. These formalisms have the ability to model both the input and output requirements of components system. In this paper, we propose a method to enrich interface automata by the semantics of actions in order to verify components interoperability at the levels of signatures, semantics, and protocol interactions of actions. These interfaces consist of a set of required and offered actions specified by Pre and Post conditions. The verification of the compatibility between interface automata reuse the L. Alfaro and T. Henzinger proposed algorithm and adapt it by taking into account the action semantics. Our approach is illustrated by a case study of the vehicle CyCab.

Object-Oriented Component-Based Design using Behavioral Contracts: Application to Railway Systems

In this paper, we propose a formal approach for the design of object-oriented component-based systems using behavioral contracts. This formalism merges interface automata describing communication protocols of components with the semantics of their operations. On grounds of consistency with the object-oriented paradigms, we revisit the notions of incremental design and independent implementability of interface automata by novel definitions of components compatibility, composition, and refinement. Our work is illustrated by a design case study of CBTC railway systems.

Component Design and Adaptation Based on Behavioral Contracts

In this paper, our objective is to propose an adaptation approach to generate a component adaptor that ensures a correct interaction between mismatched components. Compared to the related works on component adaptation, the originality of our proposition relies on two main contributions. In the first, we design component behavioral contracts in order to generate component adaptor. So, we propose to specify component interfaces as behavioral contracts, to enrich the exhibited informations in component interfaces. Our behavioral contracts express all component facets: their action signatures, their actions semantics, and their protocol. We consider that these informations are important when generating component adaptors. In the second contribution, we propose to specify component behavioral contracts with the formalism based on interface automata that we enrich to specify the semantics of component actions. So, our adaptation approach is also an extension of the interface automata approach to handle the problem of component adaptation.