Section: New Results

Multiple Services for Device Adaptive Platform for Scenario Recognition

Participants : Annie Ressouche, Daniel Gaffé, Ines Sarray, Jean-Yves Tigli.

Keywords: Synchronous Modelling, Model checking, Mealy machine, Ubiquitous Computing.

The aim of this research axis is to federate the inherent constraints of an activity recognition platform like SUP (see section  5.1 ) with a service oriented middleware approach dealing with dynamic evolutions of system infrastructure. The Rainbow team (Nice-Sophia Antipolis University) proposes a component-based adaptive middleware (WComp  [91] , [90] , [73] ) to dynamically adapt and recompose assemblies of components. These operations must obey the "usage contract" of components. The existing approaches don't really ensure that this usage contract is not violated during application design. Only a formal analysis of the component behaviour models associated with a well sound modelling of composition operation may guarantee the respect of the usage contract.

The approach we adopted introduces in a main assembly, a synchronous component for each sub assembly connected with a critical component. This additional component implements a behavioral model of the critical component and model checking techniques apply to verify safety properties concerning this critical component. Thus, we consider that the critical component is validated.

In [83] , [82] , we showed that an efficient means to define the synchronous components which allow to validate critical component behaviours, is to specify them with Mealy machines. Previously, we used a classical synchronous language (Lustre) to specify synchronous components, but the integration of the synchronous component code into WComp was not straightforward because Lustre compiler is not opened and cannot integrate new target code needed by WComp. This year, we rely on clem to design synchronous monitor as clem automata and we extend clem to generate automatically the internal code of WComp(C#).

On another hand, for some critical components, we can be led to introduce several synchronous monitors, each of them being related to a sub assembly. Then, some outputs of these synchronous monitors can be linked to the same input of a critical component. To face this problem, we introduced in [83] , [82] a composition under constraints operation, which composed all the synchronous monitors linked to a critical component according to a set of constraints telling us how the respective outputs of monitors which access the same input are combined. We proved that this operation preserved safety properties, however it cannot ensure adaptivity and incrementality. This year, we have introduced a new way to compose synchronous monitors. We introduce an additional monitor (called constrain monitor) which express as a clem Mealy machine (set of equations) the constraints and we perform a usual parallel composition of all the monitors. Moreover, we define a syntactic mean (language dcl ) to describe constraints in a generic way and we can derive automatically the constraint monitor for each specific application. In such a setting, we are able to manage the appearance and the desappearance of synchronous monitors.

Moreover, in middleware as WComp, communication is asynchronous while synchronous monitors respect the synchrony paradigm. Thus, we need to introduce in the middleware a means to transform asynchronous events into synchronous entries for synchronous monitors and the opposite to connect again the synchronous events into asynchronous design. To this aim, we introduced in WComp, specific components that receive asynchronous events and generate synchronous ones. Indeed, the part of this component is to decide how asynchronous events will be gather into a synchronous instant (logical time). To this aim, the user can choose between different politics. Then, all the events composing an instant are serialized and deserialized by the synchronous monitor. The desynchronisation operation performs the opposite way[54] .