Upper Mapping and Binding Exchange Layer (commonly abbreviated UMBEL) is a lightweight, subject concept reference structure for the Web. 
Role of UMBEL
Some may conjure up a universal 'ontology of everything' when they first encounter UMBEL. This vision is wrong and not the intent of this lightweight subject concept reference structure. But, UMBEL is trying to straddle two different worlds and world views, and that can often lead to misunderstandings and misperceptions.
- Just released UMBEL - A New Vocabulary for the Semantic Web: http://blog.semantic-web.at/2008/07/17/just-released-umbel-a-new-vocabulary-for-the-semantic-web/
- The Semantic Web puzzle - Open World assumptions: http://blog.semantic-web.at/category/ontology-engineering/