UMBEL is based on a faithful but reduced subset extraction of concepts and relationships from the OpenCyc version of the Cyc knowledge base. For example, every view of UMBEL with the Subject Concept Explorer shows a green equivalent class link to an OpenCyc concept, and the broader and narrower than relationships in UMBEL are also derived from existing OpenCyc OWL predicates.

As such, UMBEL is a lightweight reflection of these sources, but not nearly as capable nor complete. Use and relations based on UMBEL may therefore not be an accurate representation of what might be obtained in working directly with the source Cyc or OpenCyc knowledge bases.