Next Steps in Reasoning Defeasibly over Ontologies
Professor Ivan Varzinczak, from the Université d’Artois, France will present the Department of Computer Science colloquium with a talk entitled, "Next Steps in Reasoning Defeasibly over Ontologies".
Description Logics (DLs) are a family of logic-based knowledge representation formalisms with appealing computational properties and a variety of applications at the confluence of modern artificial intelligence and other areas. In particular, DLs are well-suited for representing and reasoning about ontologies and therefore constitute the formal foundations of the Semantic Web. The different DL formalisms that have been proposed in the literature provide us with a wide choice of constructors in the object language. However, these are intended to represent only classical, unquestionable knowledge, being unable to express the different aspects of uncertainty and vagueness that often show up in everyday life. Examples of these comprise the various guises of exceptions, typicality (and atypicality), approximations and many others, as usually encountered in the different forms of human quotidian reasoning. A similar argument can be put forward when moving to the level of entailment, that of the sanctioned conclusions from a knowledge base. DL systems provide for a variety of (standard and non-standard) reasoning services, but the underlying notion of entailment remains classical and therefore, depending on the application one has in mind, DLs inherit most of the criticisms raised in the development of the so-called non-classical logics. In this regard, endowing DLs and their associated reasoning services with the ability to cope with defeasibility is a natural step in their development. Indeed, the past two decades have witnessed the surge of many attempts to introduce non-monotonic reasoning capabilities in a DL setting. These range from preferential approaches to circumscription-based ones, amongst others. In spite of all the progress that has been achieved in the area, the study of non-monotonic reasoning in DLs remains a large avenue for exploration. To witness, the bulk of the effort in this direction has been put in the definition of accounts of defeasible subsumption and in the characterisation of appropriate notions of defeasible entailment relations. This suggests that existing approaches to reasoning with defeasible inheritance and typicality in ontologies may lack constructors that are important from a modelling perspective. Indeed, here we make a case for a number of additional defeasible constructs at the object level enriching the basic DL concept language and propose a corresponding preferential semantics. We show that this does not negatively affect decidability or complexity of reasoning for an important class of DLs, and that existing notions of preferential reasoning can be expressed in terms of our new constructs.
Ivan Varzinczak is a professor of computer science at Université d’Artois, France. He holds a Ph.D. (2006) in artificial intelligence from Université Paul Sabatier, France, an M.Sc. (2002) and a B.Sc. (2000) both in computer science from the Federal University of Paraná, Brazil. Before joining Université d’Artois, Ivan was a postdoctoral researcher at the CSIR Meraka Institute in South Africa and a professor at the Federal University of Rio de Janeiro, Brazil.
Ivan’s main research interest area is logic-based knowledge representation and reasoning in artificial intelligence, with focus on modal and description logics and their applications in non-monotonic reasoning, reasoning about actions and change, and the semantic web. He has co-authored more than 40 peer-reviewed publications ranging from articles in journals (JAIR, Artificial Intelligence, JANCL, Logica Universalis), full papers in international conference proceedings (IJCAI, KR, ECAI, AI, JELIA, AiML, ISWC, TARK), and papers in international workshops (NMR, Commonsense, NRAC, M4M, DL).
Ivan is a guest editor of the Special Issue of the International Journal of Approximate Reasoning (IJAR) on Defeasible and Ampliative Reasoning, and is one of the founding members and co-chair of both the ARCOE and DARe workshop series. He was the Publicity and Sponsorship Chair for KR 2016, and has been a PC member of IJCAI, KR, AAAI, ECAI, JELIA and other international conferences and workshops on several occasions.