Interactive Geometry is becoming part of the curriculum in many European countries; sharing the files of interactive geometry, the constructions, is, however difficult because of the communities are scattered between the many software systems and the many curriculum differences. The Intergeo project addresses this issue by offering a platform where cross-curriculum search and annotation can be done. The annotation language is an ontology and is made easily accessible to users; this ontology describes elementary competencies and topics and their relationships. The search functions, the management, and the access are all empowered by the semantic nature of this ontology together with the various names attached to each ontology element. This paper describes the ontology and the infrastructure that provides utility, usability, and interoperability to this knowledge corpus.