Section: Scientific Foundations

Logic-based Knowledge Representation and Reasoning

We follow the mainstream logical approach to the KRR domain. First-order logic (FOL) is the reference logic in KRR and most formalisms in this area can be translated into fragments (i.e., particular subsets) of FOL. A large part of research in this domain can be seen as studying trade-off between the expressivity of languages and the complexity of (sound and complete) reasoning in these languages. The fundamental problem in KRR languages is entailment checking: is a given piece of knowledge entailed by other pieces of knowledge (for instance from the KB)? Another important problem is consistency checking: is a set of knowledge pieces (for instance the knowledge base, KB, itself) consistent, i.e., is it sure that nothing absurd can be entailed from it? The query answering problem is a topical problem (see 3.3 ). It asks for the set of answers to the query in the KB. In the special case of boolean queries (i.e., queries with a yes/no answer), it can be recast as entailment checking.