Assemblies of Pervasive Services
Abstract: Pervasive computing is a vision about computers blending into the background, being there to assist us when we need them, but not requiring constant attention. The vision covers scenarios in the home, at work, and out in the street, and builds on the ongoing development towards an increasing number of embedded computers with network connectivity. The thesis presents the assembly as a lightweight mechanism for combination of devices and services in pervasive computing environments. The assembly is intended to be modifiable by an end user, and to facilitate ad-hoc combinations of services as well as adaptations to changes in services. It does so by separating configuration and coordination, specified in an assembly descriptor, from computation, specified in the services. It supports end-user understanding by using service descriptions that can be inspected and interacted with directly through rendered user interfaces. This gives more flexibility than approaches based on domain-level standardization. An assembly can give rise to services of its own, referred to as synthesized services. The synthesized services can be used by other assemblies in turn, for dealing with complex systems in a hierarchical way. Assemblies and services are elements of the open architecture developed in the project PalCom, and are supported by its communication and discovery protocols. The protocols target resource-constrained devices and situations with varying network connectivity, as required in several of the scenarios studied in PalCom, and they presume no central infrastructure. A central mechanism is the Pacemaker Protocol, which lets devices become aware of each other, using a heartbeat frequency that can be controlled at the application level. A language for assembly descriptors has been defined, tools have been developed, and frameworks and middleware have been implemented for the developer of PalCom services. These have been used by PalCom partners when building prototypes for scenarios, studied in cooperation with prospective end users in the fields of emergency response, landscape architecture, neonatology, and physical-functional and cognitive rehabilitation.
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