@inproceedings{nguyen07addct,
  author    = {Linh Anh Nguyen},
  title     = {Weakening {Horn} Knowledge Bases in Regular 
               Description Logics to Have {PTIME} Data Complexity},
  booktitle = {Proceedings of {Automated Deduction: 
	  	       Decidability, Complexity, Tractability ADDCT'07}},
  editor    = {S. Ghilardi and U. Sattler and 
	  	       V. Sofronie-Stokkermans and A. Tiwari}, 
  year      = {2007},
  pages     = {32-47}
}