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Recently, it has been shown that the small description logic (DL) EL, which allows for conjunction and existential restrictions, has better algorithmic properties than its counterpart FL0, which allows for conjunction and value restrictions. Whereas the subsumption problem in FL0 becomes already intractable in the presence of acyclic TBoxes, it remains(More)
Combining knowledge representation and reasoning formalisms is an important and challenging task. It is important because non-trivial AI applications often comprise different aspects of the world, thus requiring suitable combinations of available formalisms modeling each of these aspects. It is challenging because the computational behavior of the resulting(More)
We extend the description logic EL with reflexive roles and range restrictions, and show that subsumption remains tractable if a certain syntactic restriction is adopted. We also show that subsumption becomes PSpace-hard (resp. undecidable) if this restriction is weakened (resp. dropped). Additionally, we prove that tractability is lost when symmetric roles(More)
We propose an action formalism that is based on description logics (DLs) and may be viewed as an instance of the Situation Calculus (SitCalc). In particular, description logic concepts can be used for describing the state of the world, and the preand post-conditions of actions. The main advantage of such a combination is that, on the one hand, the(More)
As fragments of first-order logic, Description logics (DLs) do not provide nonmonotonic features such as defeasible inheritance and default rules. Since many applications would benefit from the availability of such features, several families of nonmonotonic DLs have been developed that are mostly based on default logic and autoepistemic logic. In this(More)
TBoxes in their various forms are key components of knowledge representation systems based on description logics (DLs) since they allow for a natural representation of terminological knowledge. Largely due to a classical result given by Nebel [15], complexity analyses for DLs have, until now, mostly failed to take into account the most basic form of TBoxes,(More)
CEL (Classifier for EL) is a reasoner for the small description logic EL which can be used to compute the subsumption hierarchy induced by EL ontologies. The most distinguishing feature of CEL is that, unlike all other modern DL reasoners, it is based on a polynomial-time subsumption algorithm, which allows it to process very large ontologies in reasonable(More)
In order to use description logics (DLs) in an application, it is crucial to identify a DL that is sufficiently expressive to represent the relevant notions of the application domain, but for which reasoning is still decidable. Two means of expressivity required by many modern applications of DLs are concrete domains and general TBoxes. The former are used(More)