Document Type

Technical Report

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Technical Report Number



Some of the most dynamic systems being built today consist of physically mobile hosts and logically mobile agents. Such systems exhibit frequent configuration changes and a great deal of resource variability. Applications executing under these circumstances need to react continuously and rapidly to changes in operating conditions and must adapt their behavior accordingly. The development of such applications demands a reexamination of the very notion of context and of the mechanisms used to manage the application response to contextual changes. This paper introduces EgoSpaces, a coordination model and middleware for ad hoc mobile environments. EgoSpaces focuses on the needs of application development in ad hoc environments by proposing an agent-centered notion of context, called a view, whose scope extends beyond the local host to data and resources associated with hosts and agents within an entire subnet surrounding the agent of interest. An agent may operate over multiple views whose definitions may change over time. An agent uses declarative specifications to constrain the contents of each view by employing a rich set of constraints that take into consideration properties of the individual data items, of the agents that own them, the hosts on which the agents reside, and of the physical and logical topology of the ad hoc network. This paper formalizes the concept of view, explores the notion of programming against views, and discusses possible implementation strategies for transparent context maintenance. We include examples to illustrates the expressive power of the view abstraction and to related it to other research on coordination models and middleware.


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