Stéphane Lavirotte

WComp middleware for ubiquitous computing: Aspects and composite event-based Web services

After a survey of the specific features of ubiquitous computing applications and corresponding middleware requirements, we list the various paradigms used in the main middlewares for ubiquitous computing in the literature. We underline the lack of works introducing the use of the concept of Aspects in middleware dedicated to ubiquitous computing, in spite of them being used for middleware improvement in other domains. Then, we introduce our WComp middleware model, which federates three main paradigms: event-based Web services, a lightweight component-based approach to design dynamic composite services, and an adaptation approach using the original concept called Aspect of Assembly. These paradigms lead to two ways to dynamically design ubiquitous computing applications. The first implements a classical component-based compositional approach to design higher-level composite Web Services and then allow to increment the graph of cooperating services for the applications. This approach is well suited to design the applications in a known, common, and usual context. The second way uses a compositional approach for adaptation using Aspect of Assembly, particularly well-suited to tune a set of composite services in reaction to a particular variation of the context or changing preferences of the users. Having detailed Aspect of Assembly concept, we finally comment on results indicating the expressiveness and the performance of such an approach, showing empirically that principles of aspects and program integration can be used to facilitate the design of adaptive applications.

SLCA, composite services for ubiquitous computing

Main concepts to handle in ambient computing applications are hard to integrate at the same time. After studying middlewares handling a part of the challenge, and after studying possiblities of main paradigms in name of CBSE and SOA, we present our Service Lightweight Component Architecture (SLCA) model, based on three main paradigms: Web services, enabling entities interoperability, dynamic discovery, and distribution, lightweight component assemblies to create composite Web services, allowing a high dynamicity, and events, giving applications reactivity and a maximal decoupling between entities, thus enabling an even higher dynamicity. This leads to conciliate both service oriented and event driven approaches in a new way to manage a graph of cooperating services in ubiquitous systems.

Service Composition Based on Natural Language Requests

The easiest way for a user to express his needs regarding a desired service is to use natural language. The main issues come from the fact that the natural language is incomplete and ambiguous, while the service composition process should lead to valid services. In this paper we propose a natural language service assemblage method based on composition templates (patterns). The use of templates assures that the composition result is always valid. The proposed system, called NLSC (Natural Language Service Composer), was implemented on the top of a service-oriented middleware called WComp and tested in an intelligent home environment.

Self-adaptation of event-driven component-oriented middleware using aspects of assembly

Pervasive devices are becoming popular and smaller. Those mobile systems should be able to adapt to changing requirements and execution environments. But it requires the ability to reconfigure deployed codes, which is considerably simplified if applications are component-oriented rather than monolithic blocks of codes. So, we propose a middleware called WComp which federates an event-driven component-oriented approach to compose distributed services for devices. This approach is coupled with adaptation mechanisms dealing with separation of concerns. In such mechanisms, aspects (called Aspects of Assembly) are selected either by the user or by a self-adaptive process and composed by a weaver with logical merging of high-level specifications. The result of the weaver is then projected in terms of pure elementary modifications of components assemblies with respect to blackbox properties of COTS components. Our approach is validated by analyzing the results of different experiments drawn from sets of application configurations randomly generated and by showing its advantages while evaluating the additional costs on the reaction time to context changing.

WComp, a Middleware for Ubiquitous Computing

Ubiquitous computing relies on computers present everywhere, at any times and in any things. Indeed with recent years advance in mobile communication technologies and the miniaturization of computer hardware, processing units are becoming invisible and a part of the environment. Middlewares for ubiquitous computing have to manage three main features specific to their environment: devices’ mobility, devices’ heterogeneity and environment’s dynamicity. The devices’ mobility, due to motion of users and their associated devices, forbids to assume that entities are known and will always be available. The second concept, entity’s heterogeneity, outlines the diversity between devices’ capabilities and functionalities provided by new smart objects. Finally, the environment high dynamicity illustrates the ubiquitous world entropy with the appearance and disappearance of devices. Devices used to create applications are thus unknown before discovering them. Then, ubiquitous computing must deal with such a dynamic software environment (called software infrastructure afterwards). As a result, future ubiquitous computing architectures must take into account those three constraints to solve ubiquitous computing challenges. Our model of middlewareWComp is based on three parts: a software infrastructure, a service composition architecture, and a compositional adaptation mechanism. To manage the dynamicity and heterogeneity of entities in the software infrastructure, we highlight the use of Web Service Oriented Architecture for Device (WSOAD). This will be discussed in section 2. Ubiquitous applications are then based on a set of Web services for devices that must interact with each other. Consumers can not edit these services. Therefore, in order to add new functionalities to the system, an application has to be a composition of services for devices. Such an application, and thus such a composition, must be modifiable at runtime. The second part of the WComp middleware enables us to make such applications by dynamically composing services from the software infrastructure. To allow reusability of newly created functionalities, and for scalability purposes, such composition can be encapsulated as a composite service. This part of the system will be presented in Section 3. Moreover, the infrastructure of ubiquitous computing applications evolves dynamically led by appearances and disappearances of objects or devices. The variation of this infrastructure is dynamic due to arbitrary node mobility, failures or energy constraints. The service composition must be as relevant as possible according to the underlying software infrastructure. Managing these

Optimized contextual discovery of Web Services for Devices

Due to more and more mobile computers moving among smart and communicating devices in our everyday life, we observe the emergence of new constraints in software design. Indeed, device heterogeneity, dynamic software variation, and frequent mobile device apparition/disappearance make software applications compulsorily adapt to their context. In this paper, we will present an enhancement of ambient computing discovery mechanisms adding context handling capabilities to Web Services for Devices. As a matter of fact, we define contextual parameters for broadcasted requests so that only devices in the „selected context” reply, which aim at reducing the overall number of exchanged messages on the network.

Définition du contexte: fonctions de coût et méthodes de sélection

This paper targets with applications running on mobile devices. We aim at developing a formalism and a framework to simplify the development of applications taking into account the context in which they are running.Following previous studies from other authors, we extend the notion of context area using distance function with cost function on context space dealing on different modes of selection.We extend the context area formalism to encompass more applications. We demonstrate on a mobile applications: the museum visit.

Safe Composition in Middleware for the Internet of Things

The Internet of Things (IoT) connects sensors, actuators and autonomous objects interacting with each other. These devices are represented by web services. Web services composition often involves conflicts between systems having access to shared devices. In our component-based middleware, our solution allows managing access to shared devices, by generating specific constraint components which guarantee the respect of some predefined composition and adaptation constraints. IoT environments are dynamic; our solution ensures adaptation to its changes by using new generated constraint components and inhibitors to deal with the appearance and disappearance of devices/applications. The main contribution in this work is the definition of a new language DCL (Description Constraint Language) that helps to generate our constraint components by describing generic constraints that must be verified on accesses to shared devices. The whole approach and its associated tools rely on the synchronous paradigm, since it has a well-established formal foundation allowing automatic proofs, and interface with most model-checkers. We can then prove and guarantee a safe composition at runtime for our IoT applications.

Adaptations interferences detection and resolution with graph-transformation approach

The adaptation of software applications is a critical need in ubiquitous computing. This adaptation should be done at runtime as a response to changes in software infrastructure. Each adaptation occurs correctly when it is separated but it may interact with other adaptations when they are composed. These interactions can affect the target behavior after adaptation. We call this interference. In this paper, we present an original approach to resolve interference. We represent applications and their adaptations by graphs; then we apply graph transformation rules on these graphs to resolve interferences.

Toward a Behavioral Decomposition for Context-Awareness and Continuity of Services

Many adaptative context-aware middleware exist and most of them rely on so-called vertical architectures that offer a functional decomposition for contextawareness. This architecture has a weak point: it does not allow the system handling both dynamics of the changing environment and applications. To avoid this, we propose an approach for context-awareness based on a behavioral decomposition, and because each behavior must complete all functionalities necessary for contextawareness, we introduce an hybrid decomposition. It consists in a functional decomposition into a behavioral decomposition. This approach derives benefits from both decomposition, first allowing to handle environment and application’s dynamics, second introducing reusability and modularity into behaviors.