formalisms that are used to represent the conceptual knowledge of an application
domain. DLs have proven successful in various application domains but their most
notable success is due to the fact that they provide the logical underpinning
of OWL, the standard ontology language for the semantic web. As a consequence
of this standardization ontologies written in OWL are getting larger and more
complex. In real world applications knowledge engineers are not only interested
in whether an ontology has a certain consequence or not, but also in why it has
this consequence. That is they want to have explanations for a given
consequence. Even for ontologies of moderate sizes, finding explanations is not
an easy task without getting help from an automated tool. In the present talk
first I am going to give an overview on DLs and then concentrate on the problem
of finding explanations in light-weight DLs.