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CHAMELEON framework

Dipartimento di Informatica
UniversitÓ degli Studi dell'Aquila

Via Vetoio, I-67010 L'Aquila (Italy)


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Context awareness and adaptation have become two key aspects to be considered while developing applications and services for heterogeneous environments.

Applications and services need to be aware of and adaptive to their context, i.e., the combination of user-centric data (e.g., information of interest for users according to their current circumstance) and resource/computer-centric data (e.g., resource limits and conditions of devices and network).

Strictly concerning CHAMELEON, context awareness identifies the capability of being aware of the user needs and of the resources required by an application and offered by the hosting execution environment (e.g., processor, memory, display, I/O capabilities, available radio interfaces, networks in reach), in order to decide whether that environment is suited to receive and execute the application in such a way that end-users expectations are satisfied. Adaptation identifies the capability of changing the application in order to comply with the current context conditions. In order to perform an adaptation it is essential to provide an actual way to model the characteristics of the application itself and of the execution environment, aiming at a high end-user degree of satisfaction depending on requested and offered SLS. In this direction, we introduces the notion of requested Service Level Specification (SLS) and offered SLS to deal with the (extra-functional) preferences of the user. Thus, while delivering services, it is useful to be able to reason about the resources demanded by an application (and its possible adaptation alternatives - i.e., different implementations) and the ones supplied by the hosting execution environment. It is worth to note that although a change of context is measured in quantitative terms, i.e., in terms of availability of (network and device) resources, an application can only be adapted by changing its behavior - i.e., its functional/qualitative specification.

In this setting, three different construction approaches towards adaptable applications might be considered: (i) self-contained applications that embed the adaptation logic as a part of the application itself and, therefore, are a-priori instructed on how to handle dynamic changes in the environment hence reacting to them at runtime; (ii) tailored applications that are the result of an adaptation process which has been previously applied on a generic version of the application; (iii) middleware-based adaptable applications in which the middleware embeds the adaptation logic in the form of meta-level information on how the applications can be adapted. Self-contained adaptable applications are inherently dynamic in their nature but suffer the pay-off of the inevitable overhead imposed by the adaptation logic. On the contrary, tailored adapted applications have a lighter code that make them suitable also for limited devices, but are dynamic only with respect to the environment at deployment time, while remaining static with respect to the actual execution, i.e., they cannot self-adapt to runtime changes in the execution environment. Considering the huge variety and limitedness of our target devices, and the complexity of the emergent networking enviroments (such as Beyond 3rd Generation (B3G) networks) would make unfeasible the deployment of a fully self-adaptive application (i.e., a potentially huge-sized self-contained application) suitable for any resulting execution environment and possible context in which the user can move.

The CHAMELEON framework is for tailored applications.