Defining a suitable semantic similarity between concept pairs of a subsumption hierarchy is becoming a generic problem for many applications in knowledge engineering exploiting ontologies. In this paper, we define a generic framework which can guide the proposition of new measures by making explicit the information on the ontology which has not been integrated into existing definitions yet. Moreover, this framework allows us to rewrite numerous measures, originally proposed in various contexts, which are in fact closely related to each other. From this observation, we show some metrical and ordinal properties. Experimental comparisons on Word-Net and on collections of human judgments complete the theoretical results and confirm the relevance of our propositions.