Distributed Context Aware Systems PDF Download

Context-awareness is a computer science concept that aims to enhance the usability of computing systems for users by unobtrusively providing services based on user and environmental context. Experimental context- aware systems typically constitute the functions of data acquisition, reasoning, context representation, context storage and context dissemination. Due to the mobile and spatial nature of the computational actors context-aware systems are usually designed with distributed software components. This distribution presents challenges in context provisioning, that is. the coordination and communication of contextual information between distributed components of the system. One of the main challenges is the diversity of settings in which context-awareness functions take place, highlighted by the heterogeneity of devices and the fluid pattern of human behaviour. Moreover, as mobile devices increasingly become the primary tool of user interaction with the environment, the complexity to adequately support awareness for diverse context applications, poses a crucial challenge in development of a large-scale context provisioning systems .. Many prototype context-aware systems have been developed that showcase context-awareness in one application domain or other but large- scale context provisioning, which also facilitates the emerging cognitive role of mobile devices, has proved elusive so far due to multi-faceted challenges in this area. Most of the research in the domain of context-aware computing focuses on context creation, prototyping context-aware applications and context use, while the challenges posed by large-scale context provisioning in such systems have not been adequately addressed. The common theme in existing efforts into developing context-aware systems has been the centralisation of the context management component that acquires, processes and distributes context information. In order to seamlessly coordinate and disseminate contextual information in a large-scale ubiquitous computing environment, a context provisioning approach is required that can overcome scalability, heterogeneity and coordination related challenges. These challenges are addressed in this work and a distributed context provisioning model is presented that can 1) disseminate multi-domain context over a large (geographic or network) scale, 2) provide coordination of context between distributed con- text producing and consuming components, 3) scale well with the increase in the system load due to context related traffic and 4) facilitate user and device mobility within the distributed system. The large-scale context provisioning model proposed by this work, entitled the Context Provisioning Architecture, is based on a federation of context brokers and uses a publish/subscribe based context coordination and communication mechanism. This thesis presents the theoretical modelling and practical implementation of the inter-broker routing of context subscriptions and notifications, management of component mobility, context modelling and context caching. Our proposed federated broker model is the first practical demonstration of federated context brokers for large-scale context provisioning. The load scalability aspect of our proposed model is experimentally evaluated against that of a centralised broker based model and the results demonstrate the improved scalability of the federated broker model. This work also proposes and demonstrates the concept of a context brokering component to manage and facilitate the evolving role of mobile devices towards cognitive context-aware devices.. The novel Mobile Context Broker component reduces the functional burden on mobile device based context consuming/providing applications. Our empirical evaluation shows a significant reduction in average energy consumption on mobile devices during the execution of context-awareness related functions in presence of the Mobile Context Broker. A minor contribution of this thesis is the use and comparison of cache replacement policies that can be utilised in a context caching component of the system. Our experiments reveal that caching is a viable strategy for improving the scalability of a context provisioning system and different cache replacement policies can be utilised within this strategy. Furthermore, this work also demonstrates a unified context model that is used not only for context representation but also for context coordination across distributed context brokers and context consuming/providing applications. Collectively, these contributions provide a holistic architectural level support and conceptual foundation that can serve as a guideline for designing large-scale context provisioning systems.