Computational Ontology for Geometry John Kontos and Iosif Armaos Department of Philosophy and History of Science, National and Kapodistrian University of Athens, HELLAS ikontos2003@yahoo.com , iarmaos@otenet.gr A system of computational ontology is presented that is useful for geometrical discovery systems and geometrical tutoring systems. The geometrical entities and processes are organised in an ontology implemented in prolog. Different kinds of queries can be answered by the system concerning the relations between the entities of the ontology. The ontology contains concepts relevant to both continuous and discrete geometrical diagrams and proofs concerning these diagrams. A graphical subsystem is implemented that demonstrates the ontological knowledge encoded in the system. The ontology system is applied to the analysis of texts stating the proofs of geometrical theory. The utility of the answering of ontological queries related to these proof texts is illustrated. Directions of the future development that concern geometric discovery and geometrical tutoring are finally presented and related to the state of the art in the field. The results obtained in the field of computational geometric reasoning illustrate the use of unambiguous ontology and strict rules that apply to proofs which may serve as models for correct scientific reasoning.