UMBEL is the Upper Mapping and Binding Exchange Layer, designed to help content interoperate on the Web.
UMBEL provides two valuable functions:
First, it is a broad, general reference structure of 28,000 concepts, which provides a scaffolding to link and interoperate other datasets and domain vocabularies, and Second, it is a base vocabulary for the construction of other concept-based domain ontologies, also designed for interoperation.
All the documentation related to UMBEL is available on UMBEL's main website.
From that website, you can easily search and browse the ontology. The UMBEL portal is supported by a rich set of APIs and functionality written in Clojure.