Although there is some collective experience in developing and using ontologies, there is no field of ontological engineering comparable to knowledge engineering. In particular, as yet, there are no standardised methodologies for building ontologies. Such a methodology would include a set of stages that occur when building ontologies, guidelines and principles to assist in the different stages, and an ontology life-cycle which indicates the relationships among stages [21]. The most well known ontology construction guidelines were developed by Gruber [6], to encourage the development of more re-usable ontologies. Recently, there has been increased effort in trying to develop a comprehensive ontology methodology (e.g. [22,23,21]). A survey is given in [24].