The PROTON Ontology (PROTo ONtology) is a basic upper-level ontology that 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.
Its design principles can be summarized as:
light-weight logical definitions
alignment with popular standards, and
good coverage of named entities and concrete domains (i.e., people, organizations, locations, numbers, dates, addresses).
It was originally developed under the auspices of the SEKT project, and first released in 2005. It is presently maintained by Ontotext.