In the emerging ubiquitous Internet scenario users require to access services and contents from anywhere, at anytime and with any device. Due to this requirement, platforms for service and content provisioning have to address several problems related to the new issues of mobility, multimodality, context awareness and content adaptation. However, current ubiquitous service provisioning platforms still suffer a main drawback: they often underestimate platform logic complexity when multiple ubiquity features should be provided. As a result, the proposed solutions lack a unified approach to the ubiquity issues and provide only limited sets of features. We claim that an integrated and comprehensive solution can stem from a simplicity principle: our approach pushes ubiquity features outside the core middleware layer, by keeping only management and coordination responsibilities. That succeeds in making the middleware design clearer and neater. In this paper we present the key architectural aspects of our middleware platform for ubiquitous dynamic context-driven service provisioning and reconfiguration. We also provide implementation details and description of typical use cases our platform successfully realizes.

The properties of a capability-based protection mechanism to be incorporated in a language for concurrent programming are presented. The protection mechanism is first abstractly characterized in terms of a protection model; the components of the protection mechanism, that is, the objects, subjects, and protection rules which govern the accessing to the objects by the subjects, are defined.

Abstract In this paper a unified set of linguistic features for providing a very flexible range of resource management strategies is presented. These features may be embedded in an object oriented programming language with abstract data type definitions. Firstly some of the more frequently used resource management strategies are illustrated and the related problems of resource allocation, access and synchronization are discussed. Then linguistic mechanisms to allow static and dynamic resource allocation, static access control and synchronization are presented. Finally some examples, reflecting a wide range of resource management strategies, are discussed in order to illustrate the application of the proposed linguistic features.

In this paper the problems met with in the performance evaluation of a process computer system are faced. After pointing out the meaning of performance evaluation for such an application and identifying the set of measurements characterising the behaviour of the controlled physical process and the computer system, the evaluation method employed is described; this consists of a set of direct software measurements and a simulation model fed by event trace. The simulation model structure is analysed and some problems relating to its feeding are illustrated. To facilitate choice of the set of measurements to be carried out and their interpretation, the system behaviour is described through a model derived from the Petri net. Finally, the results relative to the behaviour of a computer system dedicated to the control of a gaschromatographic laboratory is reported.