Robert Demolombe

Reasoning About Trust: A Formal Logical Framework

There is no consensus about the definition of the concept of trust. In this paper formal definitions of different kinds of trust are given in the framework of modal logic. This framework also allows to define a logic for deriving consequences from a set of assumptions about trust.Trust is defined as a mental attitude of an agent with respect to some property held by another agent. These properties are systematically analysed and we propose 6 epistemic properties, 4 deontic properties and 1 dynamic property.

A Simple and Tractable Extension of Situation Calculus to Epistemic Logic

The frame problem and the representation of knowledge change have deserved a lot of works. In particular, at the Cognitive Robotics Group, at Toronto, several researchers in the last ten years have produced quite interesting papers in a uni- form logical framework based on Situation Calulus [Rei91, SL93, LR94, LL98]. In [Rei91] Reiter has proposed a simple solution to the frame problem. Scherl and Levesque in [SL93] have defined an extension to Epistemic Logic to represent knowledge dynamics in contexts where some actions may produce knowledge, like, for instance, sensing actions for a robot. This approach has been extended by Lakemeyer and Levesque in [LL98] to modal operators of the kind “I know and only know”. Also, they have given a formal semantics and axiomatics, and they proved soundness and completeness of the axiomatics.

How to recognize interesting topics to provide cooperative answering

Abstract We present a method, and its formalization, to provide interesting additional information to users asking queries to a relational data base. The interesting information is defined using a knowledge base containing rules which represent the expertise of an expert having a long experience in providing information to casual users. This knowledge base also contains a high-level description of the data base content. This description uses the concepts of entity, attribute of entity, relationship and topic. The topics are related to attributes and relationships in order to be able to characterize all the information in the data base which belongs to a given semantic field. The data base and knowledge base are both formalized in first-order logic. There are two different formalization levels: the Object level to represent the data base itself, and the Meta level to represent the knowledge base which is used to transform queries. The transformed queries define the additional information which is provided to users. They can be obtained with a standard deduction mechanism. A first prototype implemented in Prolog is running.

A Modal Logical Framework for Security Policies

It turns out that security becomes more and more important in many information systems. In this paper, we are more specifically interested in confidentiality requirement. In this context, we show how knowledge representation technique based on formal logic can be used to propose a faithful model of confidentiality. Our approach is to develop a modal logic framework which combines doxastic and deontic logics. This framework enables to specify confidentiality policies -in particular, multilevel security policies- and express various types of security constraints including consistency, completeness and inference control constraints.

A deontic logic for reasoning about confidentiality

This paper presents a deontic logic Σ for reasoning about permission or prohibition to know some parts of the databjase content in the context of a multilevel confidentiality policy.

From Binary Trust to Graded Trust in Information Sources: A Logical Perspective

We present a concept of trust that integrates the trusters goal, the trustees action that ensures the achievement of the trusters goal, and the trustees ability and intention to do this action. This concept of trust is formalized in modal logic and is applied to the particular domain of trust in information sources. In this context trust may be derived, in particular, from the trusters beliefs about some properties of the information source: validity, completeness, sincerity, competence, vigilance and cooperativity. In the last part of the paper we move beyond binary trust (i.e. either i trusts j or i does not trust j ) in order to capture a concept of graded trust.

Norms, institutional power and roles: towards a logical framework

In the design of the organisation of a multiagent system the concept of role is fundamental. We informally analyse this concept through examples. Then we propose a more formal definition that can be decomposed into: the conditions that have to be satisfied to hold a role, the norms and institutional powers that apply to a role holder. Finally, we present a modal logical framework to represent these concepts.

An efficient strategy for non-Horn deductive databases

Abstract Many efficient strategies have been presented in the literature to derive answers to queries in the context of Deductive Databases. Most of them deal with definite Horn clauses. More recently, strategies have been defined to deal with non-Horn clauses but they adopt the Generalized Closed World Assumption to reduce incompleteness. In this paper we present an efficient strategy to deal with non-Horn clauses in pure logic, i.e. without any kind of assumption. This strategy is an extension of the so-called ALEXANDRE strategy to this particular context. The set of rules is transformed into another set of rules, in a compilation phase, in such a way that their execution in forward chaining simulates a variant of SL resolution. Particular attention is payed to the constants in the queries to reduce the set of derived clauses.

Trust and Norms in the Context of Computer Security: A Logical Formalization

In this paper we present a logical model of trust in which trust is conceived as an expectation of the truster about some properties of the trustee. A general typology of trust is presented. We distinguish trust in the trustees action from trust in the trustees disposition (motivational or normative disposition); positive trust from negative trust. A part of the paper is devoted to the formalization of security properties and to the analysis of their relationships with trust.

An algebraic evaluation method for deduction in incomplete data bases

Abstract Strategies used in deductive data bases try as far as possible to replace deduction in Horn clause theories T S by evaluation of relational algebra formulas in a set of ground atoms. In this paper we extend the relational algebra in order to take into account incomplete databases where incompleteness is represented by Skolem constants. We first define the notion of the extended model EM, similar to the Herbrand model, which is associated to a given theory T S . Specific satisfiability conditions applied to EM define the link between provability in T S and satisfiability in EM. Then we define an extended relational algebra to compute every ground instance of a given formula. It is shown that this algebra is always sound, and complete for a particular class of formulas which is not too restrictive.