Purpose - The purpose of this research is to address the need for a definition of metadata descriptors for use in enhancing the accuracy of bibliometric instruments of scholarly evaluation, such as the impact factor. Design/methodology/approach - A semantic vocabulary - COAP - is constructed, deployed on top of the Resource Description Framework (RDF), by extending the Friend-of-a-Friend (FOAF) schema. Findings - Anextension of the FOAF vocabulary is considered as the ability to describe a publication record such as this paper in terms of scholar contributions and participations. In order to achieve that, the FOAF vocabulary is extended. Practical implications - The application of this semantic vocabulary could be used as a way of enhancing the accuracy of source data for bibliometric evaluation instruments. Originality/value - The paper discusses how metadata descriptors can contribute to the improvement of already established scholar evaluation instruments such as the impact factor. It will be of use in the development of digital libraries.