The document proposes a five-layer semantic grid architecture with a knowledge layer on top of the Gridbus broker. The knowledge layer includes two modules: semantic description and discovery. Semantic description represents grid domain knowledge in an ontology template using Protege-OWL APIs. Semantic discovery uses the Algernon inference engine to retrieve resource information based on user queries. This knowledge layer is implemented in the Gridbus broker and can support popular middleware like Globus and Alchemi.