May 17, 2022

Now Available: New Release of OpenCitations Index of Crossref, Contains Almost 450 Million DOI-to-DOI Citation Links

From the Open Citations Blog:

As introduced in a previous blog post, COCI is the OpenCitations Index of Crossref open DOI-to-DOI references, all released as CC0 material. It is our first OpenCitations Index of open citations, in which we have applied the concept of citations as first-class data entities to index the contents of one of the major databases ofopen scholarly citation information, namely Crossref, and to render and make available this information in machine-readable RDF.

We are now proud to announce a new release of COCI, the second, which now contains almost 450 million DOI-to-DOI citation links coming from both ‘the ‘Open’ and the ‘Limited’ sets of Crossref reference data. This represents an increase of 42% in the number of indexed citations, compared with the initial release of COCI on 4th June 2018, which indexed 316,243,802 citations involving 45,145,889 bibliographic resources. In addition, the data model for COCI has now been extended so as to state directly the presence of journal self-citations and author self-citations.



As a reminder, all the data in COCI:

We plan soon to extend the OpenCitations Indexes by adding indexes of citations coming from other source datasets, including Wikidata and DataCite.

Learn Much More, View Charts in Complete Blog Post

About Gary Price

Gary Price ( is a librarian, writer, consultant, and frequent conference speaker based in the Washington D.C. metro area. Before launching INFOdocket, Price and Shirl Kennedy were the founders and senior editors at ResourceShelf and DocuTicker for 10 years. From 2006-2009 he was Director of Online Information Services at, and is currently a contributing editor at Search Engine Land.