The Citation Typing Ontology is an ontology for the characterization of citations, both factually and rhetorically. It forms part of SPAR, a suite of Semantic Publishing and Referencing Ontologies.
R. Nallapati, A. Ahmed, E. Xing, and W. Cohen. Proceedings of the 14th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, page 542--550. New York, NY, USA, ACM, (2008)