Transparency meets open citations

This post was first published on QUERTY: musings from the rabbit holea blog by Silvio Peroni

In the scholarly ecosystem, a bibliographic citation is a conceptual directional link from a citing entity to a cited entity, used to acknowledge or ascribe credit for the contribution made by the author(s) of the cited entity. Citations are one of the core elements of scholarly communication. They enable the integration of our independent research endeavours into a global graph of relationships that can be used, for instance, to analyse how scholarly knowledge develops over time, assess scholars’ influence, and make wise decisions about research investment.

A copyrighted fact

However, as citation data, i.e. pieces of factual information aiming at identifying entities and relationships among them, are of great value to the scholarly community, it has been a “scandal” that they have not been recognised as part of the commons. Indeed, only recently we have seen some efforts – such as the Initiative for Open Citations (I4OC) – that have tried to change the behind-the-paywall status quo enforced by the companies controlling the major citation indexes used worldwide, convincing scholarly publishers to support the unrestricted availability of scholarly citation data by publishing them in suitable open infrastructures, such as Crossref and DataCite.

Of course, as for many other kinds of data, putting bibliographic and citation data behind a paywall is a thread to enabling the full reproducibility of research studies based on them (e.g. in bibliometrics, scientometrics, and science of science domains), even when such studies are published in open access articles. For instance, the results of a recent open access article published on Digital Scholarship in the Humanities, which aimed to analyse the citation behaviour of Digital Humanities (DH) research across different proprietary and open citation databases, are not fully reproducible since the majority of the databases used – namely Scopus, Web of Science, and Dimensions – do not make their bibliographic and citation data openly available.

In addition, the coverage of publications and related citations in specific disciplines, particularly those within the Social Sciences and the Humanities (SSH), is inadequate compared to other fields. Usually, this is due to the limited availability of born-digital publications accompanied by a wide variety of publication languages, publication types (e.g. monographs), and complex referencing practices that may limit their automatic processing and citation extraction. As a side effect, such a partial coverage may result in a considerable bias when analysing SSH disciplines compared to STEM disciplines that usually have better coverage in existing citation databases.

Reforming research assessment

All these scenarios have at least another negative effect on the area strictly concerned with the research assessment, which often uses quantitative metrics based on citation data to evaluate articles, people, and institutions. Indeed, the unavailability and partial coverage of bibliographic and citation data create an artificial barrier to the transparency of the processes used to decide the careers of scholars in terms of research, funding, and promotions.

In the past years, several initiatives around the world have highlighted the importance of reforming research assessment exercises, such as those summarised in the following figure: the Frech National Plan for Open Science, the San Francisco Declaration on Research Assessment, the Leiden Manifesto for Research Metrics, and the recent proposal for a reform of the research assessment system by the European Commission. All these initiatives agree on a few essential characteristics necessary for having a trustful assessment system: 

  • to be open and transparent by providing machine-readableunrestricted and reusable data and methods for calculating the metrics used in research assessment exercises, and 
  • to leave to the research community, instead of commercial players, the control and ownership of the crucial infrastructures and tools used to retrieve, use and analyse such data within research assessment systems. 

Thus, the leading guideline that can be abstracted is to follow Open Science practices even when assessing research and not only when performing research.

Some initiatives pushing for reforming the principles behind research assessment systems.
Some initiatives pushing for reforming the principles behind research assessment systems.

Introducing OpenCitations

Within this context, OpenCitations (full disclosure: I am one of its directors) plays an important role, acting as a key infrastructure component for global Open Science, and pushes for actively involving universities, scholarly libraries and publishers, infrastructures, governments and international organisations, research funders, developers, academic policy-makers, independent scholars and ordinary citizens. The mission of OpenCitations is to harvest and openly publish accurate and comprehensive metadata describing the world’s academic publications and the scholarly citations that link them, with the greatest possible global coverage and subject scope, encompassing both traditional and non-traditional publications, and with a breadth and depth that surpasses existing sources of such metadata, while maintaining the highest standards of accuracy and accompanying all its records with rich provenance information, and providing this information, both in human-readable form and in interoperable machine-readable Linked Open Data formats, under open licenses at zero cost and without restriction for third-party analysis and re-use.

For OpenCitations, open is the crucial value and the final purpose. It is the distinctive mark and founding principle that everything OpenCitations provide – data, services and software – is open and free and will always remain so. OpenCitations fully espouses the aims and vision of the UNESCO Recommendations on Open Science, complies with the FAIR data principles, and promotes and practises the Initiative for Open Citations recommendation that citation data, in particular, should be Structured, Separable, and Open. 

The most important collection of such open citation data is COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations. The last release, dated August 2022, contains more than 1.36 billion citation links between more than 75 million bibliographic entities that can be accessed programmatically using its REST API, queried via the related SPARQL endpoint, and downloaded in full as dumps in different formats (CSV, JSON, and RDF). 

Collaborations between OpenCitations and other Open Science infrastructures and services.
Collaborations between OpenCitations and other Open Science infrastructures and services.

In addition to the publication of citation data, a considerable effort has been dedicated to collaborating with other Open Science infrastructures working in the scholarly ecosystem, as summarised in the figure above. Since 2020, OpenCitations has significantly benefited from the scholarly community that resulted from the 2019 selection by the Global Sustainability Coalition for Open Science Services (SCOSS) of OpenCitations as a scholarly infrastructure worthy of financial support. The community funding permitted the appointments of people dedicated to the administration, communication, community development, and maintenance and improvement of the OpenCitations software and the computational infrastructure on which it runs. In addition, OpenCitations started its involvement with OpenAIRE and the European Open Science Cloud (EOSC), and it is collaborating with other funded projects project such as RISIS2OutCiteOPTIMETA and B!SON.

While OpenCitations is currently providing a good set of citation data, which is already approaching parity with other commercial citation databases and that has already been used in a few studies for research purposes, there is still a margin for improvement. Currently, the citations included in the OpenCitations Indexes come mainly from Crossref data, one of the biggest open reference providers. However, Crossref does not cover all the publishers of DOI-based resources. Indeed, other DOI providers, in some cases, expose citation relations in their metadata, such as DataCite. In addition, DOI-based publications represent just a limited set of all the bibliographic entities published in the scholarly ecosystem. Other identifier schemas have been used to identify bibliographic entities – and, for some publications, there not exist identifiers at all!

Thus, to address these two issues, OpenCitations is working on expanding its coverage according to two different directions. On the one hand, OpenCitations is developing two new citation indexes of open references based on the holdings of DataCite and the National Institute of Health Open Citation Collection, which, together with COCI, will be cross-searchable through the Unifying OpenCitations REST API

On the other hand, OpenCitations has started working to create a new database entitled OpenCitations Meta, which will provide three major benefits. First, it will permit storing in-house bibliographic metadata for the citing and cited entities involved in all OpenCitations Indexes, including author identifiers using ORCID and VIAF identifier schemes where available. Second, it will provide better query performance than the present API system, which obtains bibliographic metadata on-the-fly by live API calls to external services, such as Crossref and DataCite APIs. Finally, it will permit indexing citations involving entities lacking DOIs, by providing them OpenCitations Meta Identifiers.

This last collection, combined with automatic tools for citation extraction from digital formats, is crucial for increasing the coverage of underrepresented disciplines and fields in bibliographic databases, such as SSH publications. One of the OpenCitations’ goals is to reduce this gap in citation coverage by setting up crowdsourcing workflows for ingesting missing citation data from the scholarly community (e.g. libraries and publishers). In the future, another contribution will be to set up tools for automatic extraction of citations that can also support small and local publishers, crucial assets for SSH research, that may find difficulties in carrying out citation extraction tasks on their own since using and maintaining a tool (or paying a company addressing those tasks on behalf of the publisher) requires extra costs beyond publishers’ finances.

To conclude: OpenCitations is one piece of a puzzle that is working to change existing scholarly practices to create an open and inclusive future for science and research in which the scholarly community owns and is responsible for its own data.

Disclaimer: This text was created during the TRIPLE Booksprint “The role of open metadata in the SSH scholarly communication” and is intended to be a contribution to the “Guidelines on the research data in the humanities” deliverable (8.5) of the TRIPLE project which will be made publicly available under the CC-BY 4.0 license.

Cite this article as: Silvio Peroni, "Transparency meets open citations," in OpenCitations blog, 27/09/2022, https://opencitations.hypotheses.org/2890.

Open citations in Informatics: current status and lines of research

This post was first published on QWERTY: musings from the rabbit hole, a blog by Silvio Peroni

A few months ago, I was invited to have a talk at the European Computer Science Symposium on an aspect of my research I particularly care about, that of open citations. What I tried to address during the presentation concerned the current status of open citation availability in a particular domain, Informatics, by using two open datasets, i.e. DBLP for gathering bibliographic metadata about relevant publications and OpenCitations’ COCI for identifying citations where such publications are involved. This post briefly introduces the preliminaries and results obtained from the material used to prepare the talk.

Open citations and where to find them

A citation is a conceptual directional link between a citing entity and a cited entity which is defined by means of specific textual devices contained in the text of the citing entity, e.g. a bibliographic reference denoted by an in-text reference pointer (e.g. “[3]” or “(Doe et al, 2021)”). While reasons for citing may vary, citations are used in academia for acknowledging others’ work and enabling building trails of relations defining how science evolves in time.

The data needed to describe a citation should include, at least, a representation of such a conceptual link and the basic bibliographic metadata to identify the citing and cited entities, i.e. those typically used for defining bibliographic references such as authors’ names, year of publication, the title of the work, venue of publication, pages, identifiers, etc. We say that a citation is open when these citation data are in the public domain and can be retrieved freely (via the HTTP protocol) in a structured and machine-readable format (e.g. JSON or RDFwithout accessing the source of citing article defining it, which, potentially, could be behind a paywall.

OpenCitations [full disclosure: I am one of its directors] is one of the founders of the Initiative for Open Citations (I4OC) and one of the open scholarly infrastructures providing open citation data through several channels (REST APIs, SPARQL endpoints, Web interfaces, full dumps in different formats). As of 31 December 2021, it makes available more than 1.2 billion open DOI-to-DOI citation links between more than 69.5 million bibliographic resources, which are mainly journal articles but also include books, book chapters, datasets, and other DOI-identified resources. The entities involved in such citations come from different domains, spanning from Medicine articles to Humanities publications, and have recently approached parity with those included in well-known proprietary services such as Web of Science and Scopus.

What about Informatics

Such a huge mass of open citations available enables us to analyse citation coverage in different scholarly disciplines, e.g. to understand which publishers contributed to the availability of open citation data in a discipline and to check what are the citation trails between different disciplines. However, to compute such citation coverage, we need to have some information that allows us to identify when a particular bibliographic resource involved in a citation belongs to the particular discipline we want to analyse. We can use information about the subject categories of publications (e.g. that of Web of Science), if included in citation indexes, to identify the discipline(s) of a given bibliographic resource. Unluckily, OpenCitations does not provide this information and, as such, we need to rely on external repositories for gathering subject categories of publications, e.g. collections of bibliographic metadata of disciplinary publications.

In the context of Informatics, there is at least one well-known resource gathering and exposing bibliographic metadata of a large part of Computer Science publications, i.e. DBLP. As of 30 December 2021, DBLP contains more than 5.9 million publications published in 1,781 journals and in the proceedings of 5,621 conferences, involving more than 2.9 million authors that are manually curated (and disambiguated) by the DBLP team.

DBLP can be used as a proxy to understand if a particular publication belongs to the Computer Science subject category. Through it, it is possible to understand how many citations in OpenCitations involve Computer Science publications by comparing the DOIs of citing and cited entities with those available in DBLP. In particular, using the OpenCitations’ COCI September 2021 dump and DBLP October dump, I found that more than 80 million citations in COCI involved at least one of the 4,637,865 entities in DBLP (considering only journal articles, conference proceedings papers, books and book chapters). As shown in Figure 1, only 39% of these citations are between citing and cited entities both included in DBLP, while the rest of them either come from or go to publications not listed in DBLP – that, potentially, could not be Computer Science publications.

Figure 1. A Venn diagram showing how many citations involving Computer Science publications (obtained from DBLP) are included in OpenCitations.

Additional information about the publishers of such DBLP entities, retrieved by querying the Crossref API and the DataCite API with entities’ DOIs, are shown in Table 1. IEEE is the publisher with the biggest number of entities of those considered for this study, and its entities are involved in more than 18.9 million incoming and 21.5 million outgoing citations. The other bigger publishers, in terms of entities and citations, are Springer, Elsevier, ACM and Wiley. It is worth mentioning that the two publishers responsible for publishing mainly Computer Science journals and a relatively low number of conference proceedings (if any), i.e. Elsevier and Wiley, are those providing the highest number of openly-available references per publication (on average, around 29 and 37 cited works for each publication respectively).

PublisherDBLP entitiesCOCI incoming citationsCOCI outgoing citations
IEEE1,730,48518,930,05521,582,093
Springer1,012,53418,482,13211,179,566
Elsevier574,86015,536,20717,019,716
ACM433,1883,695,2556,050,342
Wiley89,6623,350,1833,357,065
Table 1. The DBLP entities retrieved in the study grouped by their publisher and their incoming and outgoing citations according to COCI.

Future developments

Of course, this study does not provide full coverage of open citations in Computer Science but just a preliminary insight. First, as anticipated below, DBLP does not have the complete coverage of all CS-related publications since there are some venues that are not listed there (yet). Thus, some relevant open citations could not be extracted from COCI if these involve as citing and cited entity non-DBLP publications that belong to the CS domain. However, it is worth mentioning that no bibliographic and citation database (including commercial and proprietary ones) has a full disciplinary coverage anyway and DBLP is, probably, the most comprehensive collection of Computer Science publications metadata (something that could be assessed in future analysis).

Along the same lines, the index of open citations used, i.e. COCI, does not contain all the citations defined in CS publications, but only DOI-to-DOI citations as retrievable from Crossref data. Although Crossref is the biggest DOI provider and it is used by the majority of the big publishers,citations defined in publications with a non-Crossref DOI (e.g. DataCite) and those not having any DOI assigned (e.g. the papers published in CEUR Workshop Proceedings) are not included in COCI and, consequently, have not been used in the analysis. However, OpenCitations plans to extend its data coverage adding more sources in the next years. Thus, it would be interesting to replicate the same analysis in the future to see if and how much the coverage increase, at least in the context of Computer Science publications.

Still about coverage, currently (i.e. 31 December 2021) the only publisher of those included in Table 1 which is not providing open references through Crossref is IEEE. Indeed, while COCI includes several citations involving IEEE publications as citing entities, there is no availability of such citation after October 2018, when IEEE decided not to allow anymore Crossref Metadata Plus users to access these reference data.

Finally, analysing the preliminary results of this study, it would be interesting to understand which are the main subject categories of non-DBLP publications included in the 61% of citations shown in Figure 1 (e.g. by using the Scimago Journal and Country Rank database to retrieve their subject categories) to understand what are the citation dynamics between Informatics and other disciplines. However, I will leave the answer to this question to future analysis.

A final remark on reproducibility

Since several of the suggestions provided above start from the idea of either replicating or extending this study with additional materials and insights, it is important that all data and software used to perform the analysis are available online to permit its reproducibility. To this end, I have published both the software and the data retrieved online with open licenses to enable anyone to reuse it freely for any purpose.

Cite this article as: Silvio Peroni, "Open citations in Informatics: current status and lines of research," in OpenCitations blog, 01/01/2022, https://opencitations.hypotheses.org/1471.

New research fellowship position to work on the EOSC

OpenAIRE-Nexus is an H2020 project funded by the European Commission which aims at bringing together, within the European Open Science Cloud (EOSC), fourteen new services focused on the development and promotion of Open Science. OpenCitations is directly involved in this project through the Department of Classical Philology and Italian Studies at the University of Bologna.

In the context of this OpenAIRE-Nexus project, our goal is to make all services offered by OpenCitations compatible with OpenAIRE, so as to guarantee semantic and technical interoperability with all the other Open Science services available in the EOSC. For this purpose, we now seek applicants for a new one-year research fellowship to be held from May 2021 (renewable for an additional year), for which the application closing deadline is 31 March 2021.

The goal of the Research Fellowship is to study the current limitations of the OpenCitations infrastructure, and possible improvements to introduce into it, in order to integrate it with OpenAIRE and the EOSC. The Research Fellow, who will work in collaboration with Silvio Peroni, Director of OpenCitations, is expected to address issues relating to the provision of Web services, the management of distributed and heterogeneous databases, and data ingestion and conversion processes.

The Call for Applications (in Italian and in English) is available online on the website of the University of Bologna. It also includes an attachment with a description of OpenCitations and of the activities related to the position. The position has a net salary (exempt from income tax, after deduction of social security contributions) in excess of 20K euros per year. As indicated in the Call for Applications, candidates need to apply exclusively through the University of Bologna web portal.

For further information, please contact Silvio Peroni (email: silvio dot peroni at unibo dot it).

Cite this article as: Silvio Peroni, "New research fellowship position to work on the EOSC," in OpenCitations blog, 23/02/2021, https://opencitations.hypotheses.org/1200.

Seeking applicants for three-year research fellowship position

A year ago, at the end of 2019, OpenCitations was selected by the Global Sustainability Coalition for Open Science Services (SCOSS, https://scoss.org) for its second round of crowdfunding support, since SCOSS believes that OpenCitations aligns well with Open Science goals and is an innovative service. The goal of such support is to enable OpenCitations’ operations over the next three years as it transitions into a global scholarly infrastructure organization with a secure financial footing. As part of this work, we now plan to strengthen the current technical and computational infrastructure (server, parallel processing, backup, etc.) used by OpenCitations, which is currently hosted at the University of Bologna.

For this purpose, we now seek applicants for a new three-year research fellowship to be held from March 2021, for which the application closing deadline is 7 February 2021. The principal goals of this research fellowship are:

  1. to study the current limitations of the OpenCitations infrastructure and introduce improvements, and
  2. to design and implement new software control tools that will enable us to manage the infrastructure more efficiently.

Additionally, the selected research fellow will be expected to address issues relating to the provision of Web services, the management of distributed and heterogeneous databases, OpenCitations’ data conversion and ingestion processes involving parallel computing, and the overall security of the infrastructure. Particular attention will need to be given to data preservation and to the long-term maintenance and updating of the infrastructure.

The Call for Applications (in Italian and in English) is available online on the website of the University of Bologna. It also includes an attachment with a description of OpenCitations and of the activities related to the position. The position has a net salary (exempt from income tax, after deduction of social security contributions) in excess of 23K euros per year. As indicated in the Call for Applications, candidates need to apply exclusively through the University of Bologna web portal.

Cite this article as: Silvio Peroni, "Seeking applicants for three-year research fellowship position," in OpenCitations blog, 30/12/2020, https://opencitations.hypotheses.org/1171.

More than 733M citations now available in COCI

Today, we have published the bi-monthly release of COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations. In this latest release (dated 6 September 2020), we extended COCI with more than 11 million additional citations. Now, COCI contains more than 733 million DOI-to-DOI citation links between more than 59.4 million bibliographic entities.

These new citations were harvested from the most recent Crossref data dump, downloaded on 19 August 2020, which includes the references of articles deposited in Crossref between 4 June 2020 and 3 August 2020.

We remind you that COCI has been fully described in our open-access article

Ivan Heibi, Silvio Peroni & David Shotton (2019). Software review: COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations. Scientometrics, 121 (2): 1213-1228. DOI: https://doi.org/10.1007/s11192-019-03217-6

and that all the bibliographic and citation data in COCI:

A final remark: COCI and other OpenCitations services will be the topic of a presentation that we will have in the context of the Workshop on Open Citations and Open Scholarly Metadata 2020. The workshop is a 3-hour event for researchers, scholarly publishers, funders, policymakers, and opening citations advocates, interested in the creation, reuse, and improvement, of open citation data and open scholarly metadata, with invited speakers. No registration is needed to follow it – we hope to see you there on 9 September at 15:00 CET!

Where you can follow the Workshop on Open Citations and Open Scholarly Metadata 2020.
Cite this article as: Silvio Peroni, "More than 733M citations now available in COCI," in OpenCitations blog, 07/09/2020, https://opencitations.hypotheses.org/1136.

OpenCitations updates: interviews, outreach, research positions, citations

Several important recent events have involved OpenCitations directly as a participant. Here we introduce some of the most significant ones:

  • Our interviews during a Fireside Chat with John Chodacki during the Open Publishing Fest;
  • The SCOSS poster about OpenCitations and the other two selected infrastructures during LIBER 2020, which won the LIBER 2020 Peoples Choice Poster Award;
  • The availability of two new short-term research positions with OpenCitations for our Wellcome Trust funded project (application closing deadline: 23 July 2020); and
  • A new release of COCI, bringing the total number of open citations available in this dataset to more than 721 million.

Open Publishing Fest

The Open Publishing Fest was a decentralized on-line public event held from 18 May to 29 May

to bring together communities supporting open source software, open content, and open publishing models.

(from the Open Publishing Fest website, last visited 4 July 2020)

Within this event, John Chodaki and Cameron Neylon organised a series of sessions named “Fireside Chats” in which they invited people from the open publishing community to discuss their careers and projects. David Shotton and Silvio Peroni were the guests in one of these chats with John Chodaki, in which we talked about the origins of OpenCitations and the plans for OpenCitations’ future. The video of our chat (see link below) is available on YouTube.

The recording of the fireside chat that David Shotton and Silvio Peroni had on May 28th 2020 with John Chodaki in the context of the Open Publishing Fest.

SCOSS at LIBER 2020: promoting open infrastructures

SCOSS, the Global Sustainability Coalition for Open Science Services, which selected OpenCitations last December as worthy of community crowd-funding support as part of its second funding cycle, participated in LIBER 2020 with a poster which showcases the infrastructures that they recommend that the community financially supports.

Tweet by SCOSS on the poster presented at Liber 2020.

This poster won the People’s Choice Award and confirms the crucial activity that SCOSS is doing in making the academic community aware of the importance of providing financial support to open infrastructures like OpenCitations for the benefit of the whole of society.

A tweet by SCOSS on the document they wrote on the importance of supporting open infrastructures.

Furthermore, Giannis Tsakonas, Director in the Library & Information Center at the University of Patras (Greece), and a member of the LIBER Executive Board as head of its Innovative Scholarly Communication Steering Committee, shared a wonderful thread on Twitter about OpenCitations and the other open infrastructures (DOAB, OAPEN, and PKP) that have been selected by SCOSS in its second funding cycle.

A thread by Giannis Tsakonas about us and the other open infrastructures selected by SCOSS for their second funding cycle.

Short-term research positions open at OpenCitations in Bologna for our Wellcome Trust funded project

Wellcome Trust announced they have extended all their grants that were due to end in 2020 or 2021, including our Open Research Fund funded project entitled “Open Biomedical Citations in Context Corpus”. This project aims at providing data for each individual in-text reference pointer (aka in-text citation) and its semantic context, making it possible to distinguish references that are cited only once in the text of a paper from those that are cited multiple times, to see which references are cited together (e.g. in the same sentence), to determine in which section of the article references are cited (e.g. Introduction, Methods), and, potentially, to retrieve the function of each citation.

Some preliminary outcomes of the project have already been described in a recent blog post, and a preprint describing some of the activities of the project has also been also made available on arXiv. That paper focuses on the extensions we have made to the OpenCitations Data Model, used for the storage of data in all the OpenCitations datasets, to enable the additional metadata types resulting from the Citations in Context project to be recorded.

In the context of the funding extension to this Wellcome Trust project, the Department of Classical Philology and Italian Studies (FICLIT) at the University of Bologna has just opened two new positions for short-term (5 months) research fellowships from August to December 2020 inclusive, for which the application closing deadline is 23 July 2020. The main goals of these the short-term research fellowship are (a) to develop the software for handling the data stored in the Open Biomedical Citations in Context Corpus, and (b) to develop indexing mechanisms to analyse a large number of documents simultaneously within our local computing environment, without having to use external services.

The net salary for each research fellowship is 1,600 EUR per month, tax free. The minimal requirement to apply for one of these positions is to have a Bachelor degree, although higher qualifications in Computer Science would be beneficial. Since these are University of Bologna positions, the application forms are in Italian. However, the description of the activity plan of the research fellowships is available in both Italian and English.  We would be happy to provide further information, and help in completing the application forms if necessary, so please do not hesitate to email us.

New release of COCI with an additional 18 million citations

Every two months we are able to publish additions to COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations. This latest release (dated 4 July 2020) extended COCI with more than 18 million additional citations, so that COCI now contains more than 721 million DOI-to-DOI citation links between more than 58.8 million bibliographic entities.

These new citations were harvested from the most recent Crossref data dump, downloaded on 8 June 2020, which includes the references of articles deposited in Crossref between 4 April 2020 and 4 June 2020. As before, we will use this new release of COCI to update the Coronavirus Open Citations Dataset, the third release of which will include details about relevant additional references and publications.

We remind you that COCI has been fully described in our open-access article

Ivan Heibi, Silvio Peroni & David Shotton (2019). Software review: COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations. Scientometrics, 121 (2): 1213-1228. DOI: https://doi.org/10.1007/s11192-019-03217-6

and that all the bibliographic and citation data in COCI:

Cite this article as: Silvio Peroni, "OpenCitations updates: interviews, outreach, research positions, citations," in OpenCitations blog, 04/07/2020, https://opencitations.hypotheses.org/1095.

COCI has surpassed 700M citations

We are excited to share that COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations, was on 12 May 2020 extended with more than 47 million additional citations, and has reached a total number of more than 702 million DOI-to-DOI citation links between more than 58 million bibliographic entities.

The citations added in this the fifth release of COCI came from the most recent Crossref dump downloaded on 22 April 2020, which includes the references of the articles deposited in Crossref between 4 October 2019 and 4 April 2020. Such updates to COCI will now occur regularly at bimonthly intervals.

As a consequence, COCI now contains 702,772,530 citations, and also includes publications about the COVID-19 pandemic. We will use this new release of COCI to update the Coronavirus Open Citations Dataset, the second release of which will include details about these additional references and publications.

COCI, which is fully described in our open-access article, was one of the subjects of a multidisciplinary comparison between the major citation indexes recently published on arXiv. In addition, it has been recently mentioned on the Scholix web site as one of the implementors of the Scholix citation data format.

Finally, we wish to remind you that all the bibliographic and citation data in COCI:

Cite this article as: Silvio Peroni, "COCI has surpassed 700M citations," in OpenCitations blog, 13/05/2020, https://opencitations.hypotheses.org/1071.

Additional 31 million citations in COCI

We are proud to announce that COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations, has just been extended with more than 31 million additional citations.

As introduced in an earlier blog post and an open-access article recently published on Scientometrics, COCI is our first OpenCitations Index of open citations. In COCI, we have applied the concept of citations as first-class data entities, each identified using a unique persistent Open Citation Identifier (OCI). COCI indexes the contents of one of the major databases of open scholarly citation information, namely Crossref, and renders and makes available this information in machine-readable RDF and in other formats.

The fourth release of COCI contains more than 655 million DOI-to-DOI citation links between more than 55 million bibliographic entities. The additional 31 million citations added in the new release come from the reprocessing of previous dumps of Crossref  data. In particular, we retrieved all the citations that involve references in citing articles that were in the Crossref ‘Limited’ set when we downloaded it in October 2018. Such citing articles currently appear in the Crossref ‘Closed’ dataset due to more recent restrictive policy decisions taken by their publishers.

Finally, we wish to remind you that all the bibliographic and citation data in COCI:

Cite this article as: Silvio Peroni, "Additional 31 million citations in COCI," in OpenCitations blog, 25/03/2020, https://opencitations.hypotheses.org/1061.
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