Ontologies
A key element in building a theory is the establishment of the ontology. Ontologies for the theory can be selected from an existing ontology, a meld of ontologies from multiple sources, or constructed from first principles for the domain.
Uschold [1] has developed the first steps in a methodology for creating ontologies.
References
1. Uschold, M. 1996, 'Building ontologies: Towards a unified methodology', paper presented to the Expert Systems '96, the 16th Annual Conference of the British Computer Society Specialist Group on Expert Systems, Cambridge, UK, 16-18 December 1996.