Unification of concept terms in description logics
Journal of Symbolic Computation
Computers and Intractability: A Guide to the Theory of NP-Completeness
Computers and Intractability: A Guide to the Theory of NP-Completeness
The description logic handbook: theory, implementation, and applications
The description logic handbook: theory, implementation, and applications
Undecidability of the unification and admissibility problems for modal and description logics
ACM Transactions on Computational Logic (TOCL)
Lower bounds for natural proof systems
SFCS '77 Proceedings of the 18th Annual Symposium on Foundations of Computer Science
Replacing SEP-Triplets in SNOMED CT Using Tractable Description Logic Operators
AIME '07 Proceedings of the 11th conference on Artificial Intelligence in Medicine
Unification in the Description Logic $\mathcal{EL}$
RTA '09 Proceedings of the 20th International Conference on Rewriting Techniques and Applications
Terminological cycles in a description logic with existential restrictions
IJCAI'03 Proceedings of the 18th international joint conference on Artificial intelligence
A correspondence theory for terminological logics: preliminary report
IJCAI'91 Proceedings of the 12th international joint conference on Artificial intelligence - Volume 1
IJCAI'05 Proceedings of the 19th international joint conference on Artificial intelligence
A note on the space complexity of some decision problems for finite automata
Information Processing Letters
Relationships between nondeterministic and deterministic tape complexities
Journal of Computer and System Sciences
SAT encoding of unification in EL
LPAR'10 Proceedings of the 17th international conference on Logic for programming, artificial intelligence, and reasoning
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Unification in Description Logics has been proposed as a novel inference service that can, for example, be used to detect redundancies in ontologies. The inexpressive Description Logic EL is of particular interest in this context since, on the one hand, several large biomedical ontologies are defined using EL. On the other hand, unification in EL has recently been shown to be NP-complete, and thus of considerably lower complexity than unification in other DLs of similarly restricted expressive power. However, EL allows the use of the top concept (T), which represents the whole interpretation domain, whereas the large medical ontology SNOMEDCT makes no use of this feature. Surprisingly, removing the top concept from EL makes the unification problem considerably harder. More precisely, we will show in this paper that unification in EL without the top concept is PSPACE-complete.