elegated from the lessor to the lessee, and a machine- radio regulatory rules is to reduce or avoid interference readable policy may be delegated. When a CR crosses among users. Currently, rules regarding transmission and a regulatory boundary, the appropriate policy must be reception are enumerated in spectrum policy as pro- enabled. Policies may also be used by the system in a control function. duced by various spectrum authorities (usually in high- level, natural language). Regulators insist that even a CR The policy should use accepted standard tools and adhere to spectrum policies. To further complicate languages because the policy engine must be able to matters, a CR may be expected to operate within dif- access automatic interpretation to achieve the goals of ferent geopolitical regions and under different regula- CR applications. Policies may be written by regulatory tory authorities with different rules. Therefore, CRs agencies or by third parties and approved by regulators, must be able to dynamically update policy and select but in all cases policy is a legal or contractual operating appropriate policy as a function of situation. requirement and provability in the policy interpretation Spectrum policies relevant to a given radio may vary in engine is needed for certification. several ways: Several suggestions for policy language have emerged. The Extensible Markup Language (XML) is not ap- 1. Policies may vary in time (e.g., time of day, date, and propriate because it does not typically have inference even regulations changing from time to time). capabilities in the interpretation engines. The Ontology 2. Policies may vary in space (e.g., radio and user Inference Layer (OIL), Web Ontology Language (OWL), traveling from one policy regulatory domain to and DARPA Agent Markup Language (DAML) have another). all been explored as possible policy languages. DARPA's 3. A spectrum owner/leaser may impose policies that XG program cites the OWL language as an appropriate are more stringent than those imposed by a