In order to extract the full potential from Internet-wide content sharing and reuse, the underlying copyright issues must be taken into account. The novel requirements are not satisfied by traditional Digital Rights Management. Open licensing initiatives seem more appropriate, but they lack the required computerised support. Our proposal facilitates interoperation while providing a rich framework that accommodates copyright law and copes with custom licensing schemes. It is based on the Description Logic variant of the Web Ontology Language (OWL-DL) and constitutes an ontology that conceptualizes the copyright domain. The ontology provides the building blocks for flexible machine-understandable licenses and facilitates implementation because DL reasoners can be directly used for license checking. However, some preliminary transformations of the licenses models are required in order to overcome the Open World Assumption inherent in OWL-DL, which limits DL-based license reasoning.