Andrea Schaerf

Learn More
The timetabling problem consists in scheduling a sequence of lectures between teachers and students in a prefixed period of time (typically a week), satisfying a set of constraints of various types. A large number of variants of the timetabling problem have been proposed in the literature, which differ from each other based on the type of institution(More)
We present an integrated system for knowledge representation, calledAL -log, based on description logics and the deductive database language Datalog. AL-log embodies two subsystems, called structural and relational. The former allows for the definition of structural knowledge about classes of interest (concepts) and membership relation between objects and(More)
Termino log ica l Knowledge Representation Systems (TKRSs ) are tools for designing and using knowledge bases tha t make use of te rminological languages (or concept languages). The T K R S we consider in this paper is of pract i cal interest since it goes beyond the capabi l it ies of presently avai lable T K R S s . F i rs t , our T K R S is equipped w i(More)
tively used in the construction of knowledge-based applications in several domains (see for example Wright et al. 1993), like connguration and software engineering. Recently we have seen attempts to use them in the elds of machine learning (see for example Cohen and Hirsh 1994) and planning (see for example Devambu and Litman 1991, Weida and Litman 1992,(More)
Description iogics (aiso caiied terminoiogicai iogics, or concept ianguagesj are fragments of first-order logic that provide a formal account of the basic features of frame-based systems. However, there are aspects of frame-based systems-such as nonmonotonic reasoning and procedural rules-that cannot be characterized in a standard first-order framework.(More)
It is a common opinion that subsumption is the central reasoning task in frame-based knowledge representation languages (or concept languages). Intuitively, a concept C subsumes another concept D if the set of objects represented by C is a superset of the one represented by D. When individual objects are taken into account, the basic deduc-tive task for(More)
Most of the work regarding complexity results for concept languages consider subsumption as the prototypical inference. However, when concept languages are used for building knowledge bases including assertions on individuals, the basic deductive service of the knowledge base is the so-called instance checking, which is the problem of checking if an(More)
A recent trend in local search concerns the exploitation of several different neighbourhood functions so as to increase the ability of the algorithm to navigate the search space. In this work we investigate the use of local search techniques based on various combinations of neighbourhood functions, and we apply it to a timetabling problem. In particular, we(More)