@INPROCEEDINGS{lutz:keys03,
  author = {Lutz, C. and Areces, C. and Horrocks, I. and Sattler, U.},
  title = {Keys, Nominals, and Concrete Domains},
  booktitle = {Eighteenth International Joint Conference on Artificial Intelligence
	- IJCAI'03, Acapulco, Mexico},
  year = {2003},
  pages = {349-354},
  address = {Acapulco, Mexico},
  month = {August},
  abstract = {Many description logics (DLs) combine knowledge representation on
	an abstract, logical level with an interface to `concrete'' domains
	such as numbers and strings with built-in predicates such as <, +,
	and prefix-of. These hybrid DLs have turned out to be useful for
	reasoning about conceptual models of information systems, and as
	the basis for expressive ontology languages. We propose to further
	extend such DLs with key constraints that allow the expression of
	statements like `US citizens are uniquely identified by their social
	security number''. Based on this idea, we introduce a number of natural
	description logics and perform a detailed analyses of their decidability
	and computational complexity. It turns out that naive extensions
	with key constraints easily lead to undecidability, whereas more
	careful extensions yield NExpTime-complete DLs for a variety of useful
	concrete domains. },
}