Guy Bernard

Mobile databases: a selection of open issues and research directions

This paper reports on the main results of a specific action on mobile databases conducted by CNRS in France from October 2001 to December 2002. The objective of this action was to review the state of progress in mobile databases and identify major research directions for the French database community. Rather than provide a survey of all important issues in mobile databases, this paper gives an outline of the directions in which the action participants are now engaged, namely: copy synchronization in disconnected computing, mobile transactions, database embedded in ultra-light devices, data confidentiality, P2P dissemination models and middleware adaptability.

Disconnected operations in mobile environments

The execution of distributed applications involving mobile terminals and fixed servers connected by wireless links raises the need for handling network disconnections, both involuntary during unexpected connection breakdowns, and voluntary when the user wants to save money and energy. In this paper, we investigate how standard CORBA mechanisms (Objects By Value and Portable Interceptors) can be used for enhancing legacy CORBA-based distributed applications in order to support voluntary and involuntary disconnections. We show that the first mechanism can be used for handling easily voluntary disconnections by copying on the terminal all the data necessary for running the application in a disconnected mode. The second mechanism allows also to handle involuntary disconnections; a switch between connected mode and disconnected mode can be performed transparently to the user.

User Preferences-Based Automatic Device Selection for Multimedia User Tasks in Pervasive Environments

Multimedia task composition involves automatic matching and selection of multimedia services across various devices in the pervasive environment. During the composition process, various QoS attributes are considered for selection of the service components implementing those services. However, the existing approaches about multimedia service composition do not consider users perspective about utilizing services and devices. The automatic selection of service components keeps the user out of the whole process. The result is that the end-user may not always be satisfied with the final set of automatically chosen components and devices. In this paper, we propose a solution for multimedia task composition based on user preferences vis-a-vis device capabilities. User tasks are defined in terms of abstract services, which may also specify their requirements. Both of these criteria are considered simultaneously and a quantitative model for selection of service components and devices is presented.

Context aware deployment for mobile users

With the development of mobile computing, applications have to be accessible at any time, from any device and in any place in a wide variety of execution contexts. Consequently, applications have to adapt to different terminal capabilities both for efficiency and ergonomics. In this paper, we present a deployment infrastructure, called smart deployment infrastructure (SDI), which aims to ease the installation of large distributed applications for any kind of user terminal. SDI is designed to take into account the execution context (including available resources and the users terminal capabilities) in order to bring an application to the user and adapt it to the execution context. By considering an application as an assembly of distributed software components, SDI provides the opportunity to decide at installation time which components, among packaged components, will be instantiated on the terminal and which ones will be installed on other hosts. SDI implementation demonstrates that the deployment infrastructure offers acceptable application deployment times and, at the same time, lowers both the application execution times and terminal resource consumption.

A model for resource specification in mobile services

The proliferation of small devices and the increase in number of services created by various vendors for such devices have made SOA a primary choice for mobile software developers. However, due to software and hardware platforms heterogeneity, it is not always possible to use the write-once, use-everywhere approach. The main problem comes due to the varying capability of mobile devices and the unavailability of means to know resource requirements of mobile services. We believe that there is a need to be able to specify resource requirements so that mobile application developers could explicitly enumerate their requirements, when it comes to interoperability with other services. Towards this objective, we consider the requirements of mobile services, identified from CC/PP, a generic model of resource specification on mobile devices. We then extend the existing CC/PP model and integrate it with the SCA model for SOA. Our approach does not violate any of the CC/PP or SCA specification, while remaining neutral to the underlying technologies and platforms. An important aspect of our approach is that resources can be specified abstractly as well as concretely.

Dynamic User Task Composition Based on User Preferences

As the number of devices in a pervasive environment is increased, the number of components available on the network also grows rapidly. In such cases, it is possible to compose various applications through a combination of different sets of components. Considering the multifaceted problem of having varying device capabilities supporting a different set of protocols, and each device hosting a number of components providing the same functionality, it becomes very difficult to choose a particular device hosting a required component which can be the best-fit for the user. This becomes practically impossible when the required components are distributed across various devices in the networked environment. We propose a solution for dynamic user task composition considering user preferences, device capabilities, and heterogeneity of communication protocols. With our proposed approach, a user task can be instantiated in different environments using a different set of devices and components, depending upon their capabilities and user preferences. We propose mechanisms for modeling device capabilities and user preferences and for modeling the user task as a graph. We then propose algorithms for selection of devices based on user preferences and task requirements. Since the underlying network is also modeled as a graph, we describe an algorithm for mapping of services in the user task on to the components distributed across devices in the pervasive environment. We also give an overview of our initial implementation and some results of our evaluations.

Session Mobility of Multimedia Applications in Home Networks Using UPnP

With the increasing demand for multimedia contents and with the increased usage of small hand-held devices, a user in a home network has a number of devices at hand which may offer similar multimedia services but with varying capabilities. The user may choose one device for using a particular multimedia service at one time, and change to another device at another time. The user may, however, continue using the same service and maintain his previous session on the new device without restarting a new session. In this paper, we describe how UPnP can be used for transferring a multimedia session from a device to another in a home network. The procedure for transfer of session is based on the UPnP audio video architecture. We also describe our prototype implementation.

A quantitative model for user preferences based on qualitative specifications

With an increasing number of devices having varying capabilities and with different types of network access mechanisms, an ordinary user will consider various tradeoffs for selecting one particular device over the other for execution of his task in an ad hoc environment. We propose a model for specifying user preferences so that the selection of the best device for the user is automated. Users specify their preferences and constraints qualitatively, which are then mapped on to a quantitative utility model. Preferences can be specified both for users liking and dislike. We analyze the theory of TCP-nets as a formal model for representing and reasoning with qualitative preferences, and show how it can be used to create a quantitative preference model. Using an example scenario, the application of our model is shown and its utility against simple additive models is discussed.

A Policy-Based Approach for Resource Specification in Small Devices

A distributed application can be implemented as components, which might be available on a single host or distributed across various hosts. However, in a pervasive environment, such applications cannot be described statically in terms of the required components. This is because in such environments, the device participation is dynamic and the components described in application may not be available at the time of execution of the application. We believe that the description of the application must be generated dynamically at the time of its execution, in terms of the components available at that time. We present an approach in which an application is described in terms of abstract services, which are resolved into concrete components at runtime.When mapping services to components, their resource requirements are matched apart from their functional interfaces. Resources are also specified at both abstract and concrete levels. Only those components are selected whose interfaces and concrete resource requirements match with the abstract service interfaces and abstract resource requirements. The application composition is specified in SCA and CC/PP is used for resource specification using SCA policies.

Context Adaptation of Web Service Orchestrations

With orchestrations, one service may be realized through the cooperation of several services. This cooperation has to be formally described. In this paper, we propose to describe service orchestrations according to UML2 meta-model through three UML2 diagrams. Component diagrams describe each service external interfaces. Collaboration diagrams describe the structural composition of services. And activity diagrams describe the orchestration of services. The main contribution of this article is to mix the orchestration and composition meta-model with a context meta- model. Thus, we propose to include the descriptions of context awareness into the orchestration and composition meta-model. This approach allows application designers to describe flexible orchestration of services. Furthermore, describing compositions and their context-awareness with a model (conform to a meta-model) allows middleware with model-transformation capabilities to produce ad-hoc compositions in term of adaptation to current context execution and in term of target execution platforms. We present in this article two kinds of adaptation of context aware orchestrations: deployment time and run time adaptations.