The application of semantic technologies in a corporation sometimes requires modelling specialized ontologies under the requirements imposed by the corporate setting. Often a proof of concept needs to show the usefulness of a semantic application first, before additional investments will be made into the technology. Therefore, an initial ontology needs to be developed quickly with limited resources to demonstrate the usefulness of a semantic application. This chapter describes a practical and pragmatical approach for resource-limited modelling of ontologies. Guided by rules, this modelling approach starts with the modelling of a thesaurus which later can be extended to a full-fledged ontology. The initial step of modelling a thesaurus, allows for the development of a proof of concept first and to put the semantic application into productive use early, in order to acquire additional insights and information about its usage.