In ubiquitous computing environments, context management systems are expected to administrate large volumes of spatial and non-spatial information in geographical disperse domains. In particular, when these systems cover wide areas such as cities, countries or even the entire planet, the design of scalable storage, retrieval and propagation mechanisms is paramount. This chapter elaborates on mechanisms that address advanced requirements including support for distributed context databases management; efficient query handling; innovative management of mobile physical objects and optimization strategies for distributed context data dissemination. These mechanisms establish a robust spatially-enhanced distributed context management framework that has thoroughly been designed, carefully implemented and extensively evaluated via numerous experiments.
In the emerging and challenging ubiquitous computing environment mobile users will experience the successive enlargement and refinement of their computing and communication potential beyond their vision of the future world. They will wear smart clothes that will monitor their bio signals and act accordingly. They will carry personal communicators able to support highly complex task processing. They will hold advanced cards that will automatically handle their transactions. More sophisticated navigation and control systems will be embedded into the vehicles they drive. Invisible microcomputers and other artefacts will exist everywhere in their smart homes and offices to assist them in their every day lives. The collection all these heterogeneous computing devices will interact with intelligent sensors embedded in the surrounding environment in order to form an ambient-aware pervasive environment, which supports everyday activities related to business, education, leisure, healthcare, etc. In this respect, customers will be able to enjoy new experiences in a non-obtrusive way, as the existing infrastructure will become minimally intrusive and will exhibit inherent proactiveness and dynamic adaptability to current conditions, user preferences and environment. Eventually, as traditional systems evolve into pervasive, an important aspect that needs to be pursued is context-awareness (Xynogalas et al., 2004).
According to one of the most popular context definitions, context is basically all information that is relevant to a human-computer interaction (Dey, 2000). Theoretically, any information can become relevant for a certain task and thus, one can hardly derive context management requirements from this definition. In any case, the detection of the most important context information for characterizing the situation of a particular entity, irrespectively of the application domain, is best achieved by considering the following criterion: Human experience is strongly interrelated with location. We work when we are in our offices, we eat in a restaurant, we sleep at home, and we dance in a bar. This common understanding also influences the manner people interact with the various computing and communications systems and therefore, the way they perceive context-awareness. A system is context-aware if it uses context to provide relevant information and/or services to the user, where relevancy depends on the user’s task, and therefore, implicitly, but no exclusively, on his location. In this respect, users are more interested in context information related to their current position. Until now, the design principles in context-aware systems are mainly limited in addressing special requirements and conditions of isolated areas (e.g. smart homes, offices, artifacts, etc.) in an ad-hoc manner (Strimpakou et al., 2006). Even though the progress on this field is quite impressive, few research initiatives have attempted to design and implement a general-purpose context management system, adequate for pervasive environments. Furthermore, there are very limited or even none research efforts that have dealt with minimizing the various costs introduced during the propagation of context information to multiple remote nodes maintaining replicas of master context instances, when a multitude of different context consumers residing on these remote nodes often requests for the respective replicated context information. The research presented in this chapter focuses on developing and validating the Context Distributed Database Management System (CDDBMS), an efficient distributed heterogeneous spatial database management system that adopts a location-centric context view, integrates sophisticated selective context replica update policies for cost minimisation and is adequate for addressing the high and continuously expanding context consumer demands anytime, anyplace in future pervasive environments.
The rest of this Chapter is structured as follows. Section 2 elaborates on the motivation for the presented research work, while Section 3 briefly describes the overall CDDBMS architecture and context query handling approach. Section 4 outlines the basic CDDBMS approach for managing mobile physical objects. The context data dissemination problem is described in Section 5, a heuristic solution of which is provided in Section 6. Section 7 analyses the conducted experiments and presents the obtained evaluation results. Finally, in Section 8, a comparison of the proposed approach with the relevant state of the art work is provided, while in Section 9, conclusions are drawn and future plans are exposed.