Conservative extensions in the lightweight description logic epsilon L

We bring together two recent trends in description logic (DL): lightweight DLs in which the subsumption problem is tractable and conservative extensions as a central tool for formalizing notions of ontology design such as refinement and modularity. Our aim is to investigate conservative extensions as an automated reasoning problem for the basic tractable DL epsilon L. The main result is that deciding (deductive) conservative extensions is ExPTIME-complete, thus more difficult than subsumption in epsilon L, but not more difficult than subsumption in expressive DLs. We also show that if conservative extensions are defined model-theoretically, the associated decision problem for epsilon L is undecidable.