1. A machine-implemented method comprising: (a) the machine receiving an original ontology containing a plurality of original concepts, wherein at least one original concept is defined using a hierarchy of properties; (b) the machine applying a concept expansion mechanism to the original ontology to generate an expended ontology containing the original concepts and one or more pseudo-concepts, wherein the concept expansion mechanism comprises: (1) the machine classifying the original concepts by computing inferences using the original ontology; (2) the machine rewriting at least one original concept definition by replacing at least one defined concept appearing in the original concept definition by its expression; (3) the machine rewriting at least one sub-class axiom by replacing at least one defined concept appearing in a subsumption axiom by its expression as rewritten in step (2); (4) the machine rewriting at least one original concept in its normal form; (5) the machine generating a pseudo-concept of the expanded ontology for the at least one original concept rewritten in its normal form; and (6) the machine classifying concepts of the expanded ontology by computing inferences using the expanded ontology; and (c) the machine applying a similarity measure computation to the expanded ontology to generate a similarity measure characterizing similarity between at least two concepts in the expanded ontology, wherein the similarity measure generated using the expanded ontology provides more accurate characterization of the similarity between the at least two concepts than a corresponding similarity measure generated using the original ontology.