Description logics (DLs) are an important family of formalisms for reasoning about ontologies. CEL is the first reasoner for the description logic EL+, supporting as its main reasoning task the computation of the subsumption hierarchy induced by EL+ ontologies. The most distinguishing feature of CEL is that, unlike other modern DL reasoners, it implements a polynomial-time algorithm. The supported description logic EL+ offers a selected set of expressive means that are tailored towards the formulation of medical and biological ontologies. CEL is an OWL 2 EL reasoner (albeit currently with some limitations). To get some idea about what logical aspects can be expressed in CEL ontologies, look at our toy ontologies page.