Motik, Boris
Reasoning in Description Logics using Resolution and Deductive Databases
Universität Karlsruhe, Fak. f. Wirtschaftswissenschaften. Diss. v. 09.01.2006.
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 are added: in this case, subsumption becomes ExpTime-
hard
F. Baader, B. Ganter, B. Sertkaya, and U. Sattler. Proceedings of the 20th international joint conference on Artifical intelligence, page 230--235. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2007)