Numerical computations form an essential part of almost any real-world program. Traditional approaches to termination of logic programs are restricted to domains isomorphic to N , more recent works study termination of integer computations. Termination of computations involving real numbers is cumbersome and counter-intuitive due to rounding errors and implementation conventions. We present a novel technique that allows us to prove termination of such computations.

We suggest the concept of multitrust, which is aimed at computing trust by collectively involving a group of trustees at the same time: the trustor needs the concurrent support of multiple individuals to accomplish its task. We propose Soft Constraint Logic Programming based on semirings as a mean to quickly represent and evaluate trust propagation for this scenario. To attain this, we model the trust network adapting it to a weighted and-or graph, where the weight on a connector corresponds to the trust feedback value among the connected nodes. Semirings are the parametric and flexible structures used to appropriately represent trust metrics.

Abstract not found

Numerical computations form an essential part of almost any real-world program. Traditional approaches are restricted domains isomorphic to N, more recent works study termination of integer computations. Termination of computations involving real numbers is cumbersome and counter-intuitive due to rounding errors and implementation conventions. We present a novel technique that allows us to prove termination of such computations. Our approach extends the previous work on termination of integer computations.

Abstract The management of imprecise information in logic programs becomes important whenever the real world information to be represented is of an imperfect nature and the classical crisp true, false approximation is not adequate. In this work, we consider normal logic programs over complete lattices, where computable truth combination functions may appear in the rule bodies to manipulate truth values and we will provide a top-down query answering procedure. Keywords Logic programming · Nonmonotonic logic · Many-valued logic

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 RT W (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. 1

Multitrust provides a flexible approach to encoding trust metrics whereby definitions for trust propagation and aggregation are specified in terms of a semiring. Determining the degree of trust between principals across a trust network is, in turn, programmed as a (semiring based) soft-constraint satisfaction problem. In this paper we consider the use of semiring-based metrics in reasoning about trust between coalition-forming principals. The configurable nature of multitrust makes it well-suited to modeling trust within coalitions: whether adding more principals to a coalition increases trust or decreases trust is captured by the definition of trust aggregation within the semiring. Copyright c ○ 0000 John Wiley & Sons, Ltd. KEY WORDS:

d' ctivity eport 2006 Table of contents

facultad de informática universidad politécnica de madrid

In the analysis of logic programs, abstract domains for detecting sharing and linearity information are widely used. Devising abstract unification algorithms for such domains has proved to be rather hard. At the moment, the available algorithms are correct but not optimal, i.e., they cannot fully exploit the information conveyed by the abstract domains. In this paper, we define a new (infinite) domain ShLin ω which can be thought of as a general framework from which other domains can be easily derived by abstraction. ShLin ω makes the interaction between sharing and linearity explicit. We provide a constructive characterization of the optimal abstract unification operator on ShLin ω and we lift it to domain and to the more precise ShLin 2 abstract domain by Andy King. In the case of single binding substitutions, we obtain optimal abstract unification algorithms for such domains.