||The ISO/PAS 12006-3:2000 "Framework for object oriented information exchange" provides a metamodelfor structuring data relevant to the construction industry. The LexiCon, developed by STABU, is animplementation of that model. The LexiCon consists of a set of concepts, grouped into categories accordingto 12006-3. Each concept should be defined by a set of other concepts and is placed in a specializationhierarchy with other concepts of the same category. Ultimately, a set of basic concepts exists, from whichall the other concepts are being derived, but which can only be described by a verbal definition.The concepts in the LexiCon represent the language of the construction industry. The terms of thislanguage are extracted from numerous documents on several levels of formality, such as standards,building codes, specification systems, product information systems, technical dictionaries and classificationsystems. From these terms found in external documents concepts are then defined in the LexiCon withformal definitions. Terms from external documents can be in any human language, thus the LexiCon will bemulti-lingual.Putting the concepts in the LexiCon in a specialization hierarchy has been a process of trial and error, sofar. In principal, the number of possible hierarchies is endless, leading to also endless discussions. We arenow trying to use a more systematic approach, based on the idea that, when a concept is defined by a set ofother concepts, there will be a subset of these defining concepts that will dedicate where the describedconcept will fit into a hierarchy. A consistent hierarchy will be obtained when the subsets of definingconcepts are subsets of defining concepts on a lower level of that hierarchy. It will then be possible toreorder the hierarchy into another hierarchy, by using different sets and subsets of defining concepts.