ABSTRACT: We describe the design and use of the Ontology Pre-Processor Language (OPPL) as a means of embedding the use of Knowledge Patterns  in OWL  ontologies. Patterns provide a means of addressing the opacity and sustainability of OWL ontologies. We illustrate the specification of patterns in OPPL and discuss the advantages of its adoption by Ontology Engineers  with respect to ontology generation, transformation, and maintainability. The consequence of the declarative specification of patterns will be their unambiguous  description inside an ontology in OWL. Thus, OPPL enables an ontology engineer to work at the level of the pattern, rather than of  the raw OWL axioms. Moreover, patterns can be analysed formally, so that the repercussions of their re-use can be better understood by ontology engineers and tools implementers.