Weighted Datalog and Levels of Trust

We extend the Datalog language (we call it Datalog^w) in order to deal with weights on ground facts and to consequently compute a feedback result for the goal satisfaction. The weights are chosen from a proper c-semiring. As a second step, in order to show the usefulness of the language, we use Datalog^w as the basis to give a uniform semantics to declarative RTW (Trust Management) language family, in order to represent trust levels based on c-semirings. In this way it is possible to manage a score corresponding to a preference or cost associated to the revealed credentials, instead of a plain "yes or no" authorization result. Clearly, such a solution is more informative and allows us to treat uncertainty of facts and rules application, or different preferences for the entity roles. Trust can be then derived by choosing the best chain. The approach is rather generic and could be applied to other trust management languages.