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 originally developed by the Teknowledge Corporation and now is maintained by Articulate Software. It 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 originally concerned itself with meta-level concepts (general entities that do not belong to a specific problem domain), and thereby would lead naturally to a categorization scheme for encyclopedias. It has now been considerably expanded to include a mid-level ontology and dozens of domain ontologies.
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 SUO-KIF which has a LISP-like syntax. A mapping from WordNet synsets to SUMO has also been defined.
SUMO is organized for interoperability of automated reasoning engines. To maximize compatibility, schema designers can try to assure that their naming conventions use the same meanings as SUMO for identical words, (eg: agent, process). SUMO has an associated open source Sigma knowledge engineering environment.