Automatic Grid resource discovery and brokerage shields the Grid middleware complexities from the Grid users and leads towards an invisible but simple and robust Grid. Realizing this vision requires a machine understandable resource description and powerful correlation 1 mechanism. Semantic technologies like ontologies provide vocabularies with explicitly defined, unambiguously understandable and automatically machine-interpretable meanings which make the process of automatic resource brokerage possible. We propose a fully Ontology-based resource description, discovery and correlation mechanism. For the resource description model we have replaced the classical symmetric attribute based resource description model with an extensible asymmetric resource description model. This model provides foundation to our flexible and extensible discovery and correlation mechanism.