Luciana Benotti
title: Enhancing a Dialogue System Through Dynamic Planning
Lina Lubyte
title: Extracting and Materializing the Conceptual Schema from a Relational Database
abstract: A number of important database problems have been shown to have improved solutions by using a conceptual model (an ontology) to provide precise semantics for a database schema. At its best, such semantics of the data is captured by some kind of semantic mapping between the database schema and the conceptual model. In this talk we will concentrate on the problem of extracting and materializing the conceptual schema of a relational database designed according to Entity-Relationship techniques. To uncover the connections between the schema and a formal conceptual model, at the first part of the talk we will revisit standard database design principles from ER diagrams, thus obtaining ER-to-Relational methodology that defines correct relational representations from ER model to relational model. We fully exploit the constraints on ER objects in order to capture the information, including primary and foreign keys, uniqueness constraints, null values, domain constraints, etc. At the second step, we devise the process for extracting ER model constructs together with a set of views, assuming to have the input database designed with our proposed ER-to-Relational methodology. The semantic mapping between the database schema and the conceptual model is thus expressed, where every view, defined over the actual data, corresponds to a unique ER construct.
Luis Angel Montiel Moreno
title: Safe Beliefs Framework
abstract: Framework Safe Beliefs. A generalization of the notion of answer sets for arbitrary propositional theories. Reductions, equivalence between programs, presentation of an algorithm, based on the Davis-Putnam method, to compute safe beliefs for arbitrary propositional theories.
Evgeny Kharlamov
title: Model Theory and Calculus for The Description Logic DL-Lite
abstract: We investigate two aspects of DL-Lite: properties of models of DL-Lite knowledgebases (KBs) and a calculus for the logic. We construct examples to illustrate that in a general case DL-Lite KBs have neither finite nor least (wrt inclusion) models. We introduce the notion of a universal model for a KB and show that any satisfiable DL-Lite KB has a universal model. We also show that a chase of a knowledge base is a universal model. We show that for answering conjunctive queries (CQs) over a DL-Lite KB it suffices to evaluate it only over a universal model of the KB, and consequently, over a chase of the KB. In general the chases of a KB may be infinite. We identify a class of KBs for which all chases are finite and, moreover, CQs can be answered in polynomial time. However, it turns out that, also for KBs that have an infinite chase, it is possible to answer CQs in finite time. We do this by defining a calculus that takes as input a KB and a CQ and allows one to derive all answers. We show how a rewriting algorithm presented by Calvanese at all. can be obtained by imposing a specific control strategy on the calculus.