UMBEL

[4] The grounding of this information occurs by common reference to the permanent URIs for the UMBEL concepts; the connections within the UMBEL upper ontology enable concepts from sources at different levels of abstraction or specificity to be logically related.

Since UMBEL is an open-source extract of the OpenCyc knowledge base, it can also take advantage of the reasoning capabilities within Cyc.

[13] Including OpenCyc, UMBEL has about 65,000 formal mappings to DBpedia, PROTON, GeoNames, and schema.org, and provides linkages to more than 2 million Wikipedia pages (English version).

All of its reference concepts and mappings are organized under a hierarchy of 31 different "super types",[14] which are mostly disjoint from one another.

Each of these "super types" has its own typology of entity classes to provide flexible tie-ins for external content.