We propose a first-order model as a possible formal basis for normative agent systems (NAS). The model allows us to describe the execution of actions in time and the use of dynamic norms. We present its application to the detection of the violation cases and to optimal scheduling.

We propose a first-order model as a possible formal basis for normative agent systems (NAS). The model allows us to describe the execution of actions in time and the use of dynamic norms. We also present its operational aspect which is based on the reduction of the deontic constraints to temporal ones. In order to show the applicability of the model we briefly describe a logic programming implementation and we present two types of applications: the detection of the violation cases and the prototype of a scheduler with deontic and temporal constraints.

This paper addresses the problem of granularity in temporal representation in the context of text analysis. In contrast with other fields where granularity levels are essentially quantitative, in natural language the different levels are not always precisely defined and granularity is of a more subtle and qualitative nature. A model is proposed for representing such phenomena, based on time units and time units intervals. Time units represent chunks of time which are considered indivisible at a given granularity level, but which may be refined and contain other time units or intervals at a higher granularity level. The structure of the set of time units and intervals is studied and a relation algebra is defined which extends the traditional Allen's Point or Interval Algebra. Weak and strong representations of this algebra are proposed. We claim that such representations, called grained temporal structures, are adequate for coping with dynamic qualitative changes of granularity. A logic with restricted quantifiers is proposed for formalizing temporal knowledge and examples are discussed which show the relevance of the model for natural language analysis.

This paper presents a method for automated deduction in first-order modal logic. The modal logic systems under consideration are arbitrary systems of type KD, KD4, KT, KT4, KT5 (though not all results hold for the latter), with the constant domain semantics, accepting flexible and rigid function and predicate symbols as well. The method works as follows. With any modal system S, we associate an equational theory E(S) in some classical first-order language with sorts (‘path logic’), and we define a translation T from modal to path logic, such that any formula B is satisfiable with respect to S semantics iff T(B) is E(S)-satisfiable. The question of modal theorem proving then amounts to theorem proving in some equational theories. In this paper we use Plotkin's E-resolution, which provides ‘free of charge’ a framework immediately applicable to path logic. There is however one important problem left: some of the considered equational theories possess an associative operator, so that complete sets of unifiers (CSUs) may very well be infinite. The problem is overcome by observing that the formulae obtained by translation from modal logic belong to some fragment of path logic, characterized by the so-called ‘unique prefix property’ (UPP). Then a special Skolemization procedure preserving UPP is de-fined, and we give a unification algorithm for UPP terms, which computes finite CSUs.