This comes from the SKOS list. Bernard Vatant pointed towards a basic upper level ontology created within the SEKT (Semantically Enabled Knowledge Technologies) project (2004-2007).
The project worked on combining three core research areas: ontology management, machine learning and natural language processing.
Among other things, this project demonstrated how pre-existing knowledge in the form of a basic upper-level ontology can be used for metadata generation and as a groundwork for the overall knowledge modelling and integration strategy of a KM environment.
The PROTON ontology, itself, contains about 300 classes and 100 properties, providing coverage of the general concepts necessary for a wide range of tasks, including semantic annotation, indexing, and retrieval of documents.
Base upper-level ontology (BULO) Guidance introduces and documents the PROTON ontology.