Input data for Open Citations – the PMC Open Access Subset

"The Open Citations Project has to date worked exclusively with the Open Access subset (OASS) of PMC. As of 24 January 2011, there were 204,637 OASS articles, including a few published before 1980. In almost all of these OASS articles, the reference lists were nicely marked up in NLM-DTD XML, making the task of identifying individual references straightforward. In a few cases, the articles were present as scanned page images, lacking any internal markup – those we were unable to process. From the XML reference lists of these papers, we were able to identify and extract 6,325,178 individual references, which, together with the bibliographic information we had on the OASS articles themselves gave us 6,529,815 independent bibliographic records of both citing and cited entities...."