Pushing the EL Envelope

Recently, it has been shown that the small descrip- tion 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 inFL0 becomes already in- tractable in the presence of acyclic TBoxes, it re- mains tractable in EL even with general concept inclusion axioms (GCIs). On the one hand, we ex- tend the positive result forEL by identifying a set of expressive means that can be added toEL with- out sacrificing tractability. On the other hand, we show that basically all other additions of typical DL constructors toEL with GCIs make subsump- tion intractable, and in most cases even E XPTIME- complete. In addition, we show that subsumption inFL0 with GCIs is EXPTIME-complete.