A pervasive computing system (PCS) requires that devices be context aware in order to provide proactively adapted services according to the current context. Because of the highly dynamic environment of a PCS, the service adaptation task must be performed during device operation. Most of the proposed approaches do not deal with the problem in depth, because they are either not really context aware or the problem itself is not thought to be dynamic. Devices in a PCS are generally hand-held, that is, they have limited resources, and so, in the effort to make them more reliable, the service adaptation must take into account this constraint. In this paper, we propose a dynamic service adaptation approach for a device operating in a PCS that is both context aware and limited resources aware. The approach is then modeled using colored Petri Nets and simulated using the CPN Tools, an important step toward its validation. 1. Introduction The main goal of a PCS is to provide adapted services proactively (i.e., without explicit intervention of the user) to both users and applications, according to the current context. By “provide adapted services,” we mean that the services must be delivered according to the current context, which requires a good understanding and use of that context. One important characteristic of a PCS environment is highly dynamic change, caused by the mobility of users and devices. In order to support the user in his everyday tasks, devices must become more autonomic, requiring minimum or no human intervention. Several approaches have been proposed for service adaptation, some of them using the classic strategy of specifying a set of rules for each service and associating them with every possible context configuration. The disadvantage of such approaches is that the rules are set out before putting the system into operation (static, rather than dynamic application). In addition, the developer has to predict all possible context configurations, which may not be evident at the time. Other approaches are based on a weak specification of context elements, and this has a great impact on the adaptation task. Moreover, the existing service adaptation methods are not considered to be context-aware, and context awareness is a key feature of a PCS. Even existing context-aware service adaptation approaches are superficial and do not deal with the issue in depth, because they are either specific to a particular domain or based on an inappropriate definition of context. Moreover, related work does not consider the very limited resources of a device
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