Computer Laboratory

Technical reports

Context aware service composition

Maja Vuković

October 2007, 225 pages

This technical report is based on a dissertation submitted April 2006 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Newnham College.

Abstract

Context aware applications respond and adapt to changes in the computing environment. For example, they may react when the location of the user or the capabilities of the device used change. Despite the increasing importance and popularity of such applications, advances in application models to support their development have not kept up. Legacy application design models, which embed contextual dependencies in the form of if-then rules specifying how applications should react to context changes, are still widely used. Such models are impractical to accommodate the large variety of possibly even unanticipated context types and their values.

This dissertation proposes a new application model for building context aware applications, considering them as dynamically composed sequences of calls to services, software components that perform well-defined computational operations and export open interfaces through which they can be invoked. This work employs goal-oriented inferencing from planning technologies for selecting the services and assembling the sequence of their execution, allowing different compositions to result from different context parameters such as resources available, time constraints, and user location. Contextual changes during the execution of the services may trigger further re-composition causing the application to evolve dynamically.

An important challenge in providing a context aware service composition facility is dealing with failures that may occur, for instance as a result of context changes or missing service descriptions. To handle composition failures, this dissertation introduces GoalMorph, a system which transforms failed composition requests into alternative ones that can be solved.

This dissertation describes the design and implementation of the proposed framework for context aware service composition. Experimental evaluation of a realistic infotainment application demonstrates that the framework provides an effcient and scalable solution. Furthermore, it shows that GoalMorph transforms goals successfully, increasing the utility of achieved goals without imposing a prohibitive composition time overhead.

By developing the proposed framework for fault-tolerant, context aware service composition this work ultimately lowers the barrier for building extensible applications that automatically adapt to the user’s context. This represents a step towards a new paradigm for developing adaptive software to accommodate the increasing dynamicity of computing environments.

Full text

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BibTeX record

@TechReport{UCAM-CL-TR-700,
  author =	 {Vukovi{\'c}, Maja},
  title = 	 {{Context aware service composition}},
  year = 	 2007,
  month = 	 oct,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-700.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-700}
}