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Open distributed environments, such as the World Wide Web, facilitate information sharing but provide limited support to the protection of sensitive information and resources. Trust negotiation (TN) frameworks have been proposed as a better solution for open environments, in which parties may get in touch and interact without being previously known to each other. In this paper, we illustrate Protune, a rule-based TN system. By describing Protune, we will illustrate the advantages that arise from an advanced rule-based approach in terms of deployment efforts, user friendliness, communication efficiency, and interoperability. The generality and technological feasibility of Protune's approach are assessed through an extensive analysis and experimental evaluations.

Trust and policies are going to play a crucial role in enabling the potential of many web applications. Policies are a well-known approach to protecting security and privacy of users in the context of the Semantic Web: in the last years a number of policy languages were proposed to address different application scenarios. The first part of this chapter provides a broad overview of the research field by accounting for twelve relevant policy languages and comparing them on the strength of ten criteria which should be taken into account in designing every policy language. By comparing the choices designers made in addressing such criteria, useful conclusions can be drawn about strong points and weaknesses of each policy language. The second part of this chapter is devoted to the description of the Protune framework, a system for specifying and cooperatively enforcing security and privacy policies on the Semantic Web developed within the network of excellence REWERSE. We describe the framework's functionalities, provide details about their implementation, and report the results of performance evaluation experiments.

Traditional protection mechanisms rely on the characterization of requesters by identity. This is adequate in a closed system with a known set of users but it is not feasible in open environments such as the Web, where parties may get in touch without being previously known to each other. In such cases policy-driven negotiation protocols have emerged as a possible solution to enforce security on future web applications. Along with this setting, we illustrate Protune , a system for specifying and cooperatively enforcing security and privacy policies (as well as other kinds of policies). Protune relies on logic programming for representing policies and for reasoning with and about them.