The features of a new generation of terminological systems are introduced: they are computer-based, multihierarchical, extensible, mappable. This performance is achieved by a compositional approach: each phrase is systematically represented by predefined descriptors, according to a “categorial structure” (a model of semantic categories and their relations). A terminological system is therefore made of four interrelate components: categorial structure, system of descriptors, system of phrases and their systematic representations. The role of the European standardization body (CEN) to support the development of such terminological systems is outlined.