Abstract: An Ontologybased approach to define the authorization policies of an RBRBAC model was proposed, by which one can effectively define complex attribute expressions, quasiorder relation definition among attribute values and role hierarchies among roles in the OWL style policies. Comparison between attribute expressions without identical syntax structures is permitted to gain an insight into the relationships of all kinds of authorization rules. We can make authorization decision and perform seniority levels reasoning via an OWL reasoner. Moreover, conflicts among related authorization rules can be detected by consistency check.

Key words: OWL, RBRBAC model, authorization policy, attribute expression