Editing Description logic (section)

==Inference==
===Decision problems===
In addition to the ability to describe concepts formally, one also would like to employ the description of a set of concepts to ask questions about the concepts and instances described. The most common decision problems are basic database-query-like questions like ''instance checking'' (is a particular instance (member of an ABox) a member of a given concept) and ''relation checking'' (does a relation/role hold between two instances, in other words does '''a''' have property '''b'''), and the more global-database-questions like ''subsumption'' (is a concept a subset of another concept), and ''concept consistency'' (is there no contradiction among the definitions or chain of definitions). The more operators one includes in a logic and the more complicated the TBox (having cycles, allowing non-atomic concepts to include each other), usually the higher the computational complexity is for each of these problems (see [http://www.cs.man.ac.uk/~ezolin/dl/ Description Logic Complexity Navigator] for examples).