In this paper, I introduce a brief history of open citations, their main characteristics and use in the context of OpenCitations, a scholarly infrastructure organisation dedicated to open scholarship and the publication of open bibliographic and citation data using Semantic Web technologies. has drastically changed how we think about academic publishing and science. Publishers have adopted Web Standards to create and deliver their products quickly and to a broader audience. Standards, guidelines, and services based on Web technologies have been proposed in the past 30 years to increase the discoverability of academic products and publications, improve research practices and allow reusability of scholarly data in diferent applicative contexts. Open citations are no exception.
https://essepuntato.it (S. Peroni)
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that this paper received (even if the data are not openly accessible). A few years later, CiteSeerX
[
However, the tipping point for open citations was when, in 2009, David Shotton
introduced the concept of semantic publishing [
The idea of providing open citations was spread to the scholarly and publishing community in the following years in two diferent editions of the Annual Conference of Open Access Publishers (OASPA, https://oaspa.org/conference/). Both David Shotton’s talk at OASPA 2013 and Dario Taraborelli’s speech at OASPA 2016 highlighted the essential need to release citation data as soon as possible for the whole scholarly community.
Since 2016, everything has started to change on a large scale. The importance of open
citations got a broader audience and led to the introduction of OpenCitations [
In the previous section, I used the concept of open citations several times. However, I have not clarified what it is about and the characteristics a citation must have to be claimed as open. However, first, it is necessary to explain what I refer to when I mention the word citation.
A bibliographic citation is a conceptual directional link from a citing entity to a cited entity
to acknowledge or ascribe credit for the contribution made by the authors of the cited entity.
This link is defined using particular textual devices such as a bibliographic reference in the
reference list, denoted by an in-text reference pointer – e.g. “[
The citation data related to a particular citation must include the representation of such a conceptual directional link and the basic metadata of the citing entity and the cited entity, i.e. suficient information to create or retrieve textual bibliographic references for each of the entities involved in the citation (i.e. the citing entity and the cited entity).
A bibliographic citation is an open citation when the data needed to define the citation are
compliant with the following principles [
These principles have been thoroughly followed in the technical developments of OpenCitations, introduced in the following section.
OpenCitations (https://opencitations.net) [
We provide the OpenCitations Data Model [
Our primary database, COCI (the OpenCitations Index of Crossref open DOI-to-DOI citations) [12], currently hosts more than 1.29 billion citations. All these citations have been made available in Linked Open Data. They can be accessed programmatically using our REST API by specifying either publication’ DOI or the Open Citation Identifier (OCI) [ 13] identifying the complete citation, i.e. the relation entity A cites entity B.
Since 2020, OpenCitations has significantly benefited from crowdfunding from the scholarly community, which has resulted from (a) the Global Sustainability Coalition for Open Science Services’s (SCOSS, https://scoss.org) selection of OpenCitations as a scholarly infrastructure worthy of support, and (b) its involvement in international projects, such as the OpenAIRENexus project (https://www.openaire.eu/openaire-nexus-project) and RISIS project (https:// www.risis2.eu/).
OpenCitations espouses the UNESCO principles of Open Science [14], the Principle of Open Scholarly Infrastructures [15], the FAIR data principles that data should be Findable, Accessible, Interoperable, and Reusable [16], and the I4OC principles that citation data should be Structured, Separable, and Open (https://i4oc.org/#goals). In compliance with these values, one of OpenCitations’ main priorities is to keep its services, software, and data always without charge under open licenses (CC0 for data and ISC for software) to foster their maximum reuse.
This undeniable aspect of keeping all OpenCitations data and services free leads to an acknowledged sustainability issue, principally in terms of salaries and technical infrastructure costs. OpenCitations can rely on an international network of generous supporters that apply for membership and donation programmes. We are grateful to the institutions that believe in our mission and values. However, we are already far from being a fully financially sustained infrastructure, and we still need help from the global scholarly community to keep open bibliographic and citation data and related services available for many years and to reach the following goals: • to provide high-quality metadata with full provenance relating to scholarly publications and the citations that link them, including those in areas such as the humanities and social sciences, the global south, and non-English publications; • to expand our coverage into the ‘grey literature’ of reports, patents, datasets, software, etc.; • to surpass in terms of coverage and quality – and thereby provide an open and free alternative to – the major commercial citation indexes; • to provide the open data crucial for research in bibliometrics and scientometrics, and the creation of transparent and reproducible metrics for research assessment; • to continue developing and making public free and open-source software (FOSS) with relevant functionality and our open services built over our data.
We (scholars, institutions, founders, etc.) can make a diference and create an open, inclusive future for science and research. OpenCitations is a plural: together, we are OpenCitations.
I want to thank David Shotton and Chiara Di Giambattista, who provided insightful discussions, materials and feedback which has been included in this paper, and all the people working for and supporting OpenCitations. This work has been funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 101017452 (OpenAIRE-Nexus). 2020, volume 12507 of Lecture Notes in Computer Science, Springer, Cham, Switzerland, 2020, pp. 447–463. doi:1 0 . 1 0 0 7 / 9 7 8 - 3 - 0 3 0 - 6 2 4 6 6 - 8 _ 2 8 . [12] I. Heibi, S. Peroni, D. Shotton, Software review: COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations, Scientometrics 121 (2019) 1213–1228. doi:1 0 . 1 0 0 7 / s 1 1 1 9 2 - 0 1 9 - 0 3 2 1 7 - 6 . [13] S. Peroni, D. Shotton, Open Citation Identifier: Definition, 2019. URL: https://doi.org/10.
6084/m9.figshare.7127816. [14] UNESCO, UNESCO Recommendation on Open Science, Programme and meeting document SC-PCB-SPP/2021/OS/UROS, 2021. URL: https://unesdoc.unesco.org/ark:/48223/ pf0000379949. [15] G. Bilder, J. Lin, C. Neylon, The Principles of Open Scholarly Infrastructure, 2020. URL: https://doi.org/10.24343/C34W2H. [16] M. D. Wilkinson, M. Dumontier, I. J. Aalbersberg, G. Appleton, M. Axton, A. Baak, N. Blomberg, J.-W. Boiten, L. B. da Silva Santos, P. E. Bourne, J. Bouwman, A. J. Brookes, T. Clark, M. Crosas, I. Dillo, O. Dumon, S. Edmunds, C. T. Evelo, R. Finkers, A. GonzalezBeltran, A. J. Gray, P. Groth, C. Goble, J. S. Grethe, J. Heringa, P. A. ’t Hoen, R. Hooft, T. Kuhn, R. Kok, J. Kok, S. J. Lusher, M. E. Martone, A. Mons, A. L. Packer, B. Persson, P. Rocca-Serra, M. Roos, R. van Schaik, S.-A. Sansone, E. Schultes, T. Sengstag, T. Slater, G. Strawn, M. A. Swertz, M. Thompson, J. van der Lei, E. van Mulligen, J. Velterop, A. Waagmeester, P. Wittenburg, K. Wolstencroft, J. Zhao, B. Mons, The FAIR Guiding Principles for scientific data management and stewardship, Scientific Data 3 (2016) 160018. doi:1 0 . 1 0 3 8 / s d a t a . 2 0 1 6 . 1 8 .