The Suggested Upper Merged Ontology or SUMO is an upper ontology intended as a foundation ontology for a variety of computer information processing systems. It was developed by Teknowledge Corporation and is one candidate for the "Standard Upper Ontology" that IEEE working group 1600.1 is working on. It can be downloaded and used freely.
SUMO was first released in December 2000. It defines a hierarchy of SUMO classes and related rules and relationships. These are formulated in a version of the language KIF which has a LISP-like syntax. A mapping from WordNet synsets for nouns and verbs to SUMO classes has also been defined.