Find OpenCitations on Infra Finder, a new tool to discover and support Open Infrastructures

If you are a leader of a Library or a Research Institution and would like to learn more about the existing open infrastructures that could help your institution to evolve in the research environment, but you don’t know where to look for, you can now use Infra Finder, a brand-new tool aimed at foster discovery, adoption, and investment for open infrastructure services. Infra Finder is launched by Invest in Open Infrastructure (IOI), and is designed to be the go-to resource for anyone navigating the complex landscape of infrastructure services and standards enabling open research and scholarship. 

The tool stems from the feedback collected from the community after the launch, in 2022, of the Catalog of Open Infrastructure Services pilot project in 2022, from which IOI decided to re-envision what outcomes they could affect and rethink what solutions could look like, also by furthering the Open Science principles conveyed by UNESCO’s Recommendation on Open Science, the Principles of Open Scholarly Infrastructure, and other Open Science initiatives and guidelines.  

We are happy to announce that OpenCitations is among the 56 infrastructures which have accepted IOI’s invitation to be included in this first release of Infra Finder. During its development, IOI team has been constantly collecting feedback from the infrastructures involved, and has conducted user testing to understand how different people might approach it. In OpenCitations we believe that Infra Finder could serve as an helpful tool to make OpenCitations and the other infrastructure services more visible to a wider and diverse community. Infra Finder allows users to easily find and compare the catalogued services, and its intuitive use could work as a starting point towards the creation of a greater awareness of existing open infrastructures, thus leading users to further explore their features and services and, hopefully, to consider the possibility of support their sustainability. 

IOI is currently planning to include new services in Infra Finder: if you are part of an organization that would like to be included, you can apply by filling out their Expression of Interest form. IOI will give two identical webinars to share with the community more details about the background and features of Infra Finder and on how interested infrastructure services can express interest in being listed. Register here to the either slot:  

May 2, 2024, 1600 UTC / 12pm Eastern 

May 3, 2024, 1400 UTC / 10am Eastern (in your time zone) 

The IOI blog post for the launch is available at  

OpenCitations Access Tokens: how they work and why they are important

Since its inauguration in 2010, OpenCitations has always granted free access to its services to users throughout the world, with no requirement for registration or sign-up. Programmatic access to OpenCitations data can be obtained either via our SPARQL endpoints and our REST APIs. In addition, OpenCitations data – available in CSV, Scholix, and RDF formats – can be downloaded from data dumps made periodically and stored on Figshare, so as to enable large-scale analyses using the whole content of the data sets, and also be obtained via our user-friendly text-based search and browsing interfaces.

One of OpenCitations’ priorities is (and will always be) to keep its data globally open and available at zero cost and without restriction for third-party analysis and re-use. As a matter of sustainability, OpenCitations relies on financial support from the scholarly community, which includes those institutions that use OpenCitations data. However, OpenCitations has not so far had in place a proper system to monitor its users, and the main evidence of the impact of OpenCitations in different academic fields and countries has been incompletely obtained from direct contacts with our members and donors across the world, our collaborations with international projects, and the interactions on our social platforms (Twitter and LinkedIn).

We would now like to institute a system that enables us to follow the usage and assess the impact of OpenCitations more reliably. For this purpose, we are now happy to announce the launch of the OpenCitations Access Token System for access to the OpenCitations data and services.

An OpenCitations Access Token is an opaque character string that anonymously identifies a unique user of the OpenCitations APIs. OpenCitations assigns an access token only if authorized to do so by each user, who can request a token by inserting his/her email address into the access form and clicking “Get token”. Upon submission of such a request, each user will automatically receive a personal access token by email. Users can save their personal access token and reuse it every time calling the APIs of OpenCitations, by passing it as a value for the key access-token in the header of each API call. 

Obtaining and using an OpenCitations Access Token is thus easy. It only requires a simple form request, and then the insertion of your personal token into the API call header when using OpenCitations REST APIs. OpenCitations will not store users’ email addresses or any personal information, so that the users’ privacy will be totally safeguarded. The token system just provides a simple mechanism for identifying unique users, for which the use of IP addresses is insufficient.

Obtaining an OpenCitations Access Token will take the user only a few seconds and needs to happen only once. You can request your OpenCitations Access Token here 

Use of an OpenCitations Access Token is not compulsory. However, token use will help OpenCitations incredibly, by enabling us to monitor the number of the unique users accessing our data and services, providing objective anonymized evidence of the number of institutions and researchers accessing our data either occasionally or on a regular basis, which we can then employ to demonstrate the usefulness of OpenCitations in the research environment. While the token system will initially be employed just for API calls (the most used service we offer), it will subsequently be extended to our other forms of data access.

OpenCitations exists for the people that use its data for research purposes every day, and thanks to their support. This is why obtaining precise knowledge of how many researchers and institutions are accessing our services is essential to us, since it will enable us to present the uniqueness and value of OpenCitations to new communities of stakeholders, and thus to make it possible to enlarge the already enthusiastic and diverse group of people and institutions supporting and using our Open Science Infrastructure.

To summarize: Getting and using an OpenCitations Access Token is voluntary, easy, and does not cost you anything. However, it will help OpenCitations a great deal. Please get your own token now, and use it next time you access OpenCitations. Thank you very much!


Citations as First-Class Data Entities: The OpenCitations Corpus

Requirements for citations to be treated as First-Class Data Entities

In my introductory blog post, I listed five requirements for the treatment of citations as first-class data entities.  The third of these requirements is that they must be storable, searchable and retrievable in an open database designed for bibliographic citations.

In this post, I describe the current status of the OpenCitations Corpus, a well-structured open database specifically developed by OpenCitations and designed to store information about bibliographic citations as Linked Open Data, encoded in RDF (specifically JSON-LD).

What is OpenCitations?

OpenCitations ( is an scholarly infrastructure organization that has created and is currently expanding the coverage of the Open Citations Corpus (OCC), an open repository of scholarly citation data made available under a Creative Commons CC0 public domain dedication, which provides in RDF accurate citation information (bibliographic references) harvested from the scholarly literature.

The Co-Directors of OpenCitations are David Shotton, Oxford e-Research Centre, University of Oxford ( and Silvio Peroni, Department of Computer Science and Engineering, University of Bologna (

We are committed to open scholarship, open data, open access publication, and open source software.  We espouse the FAIR data principles developed by Force11, of which David Shotton was a founding member, and the aim of the Initiative for OpenCitations (I4OC), of which David Shotton and Silvio Peroni were both founding members, to promote the availability of citation data that is structured, separable, and open.

The principal activity of OpenCitations to date has been the establishment and population of the OpenCitations Corpus.

Holdings of the OpenCitations Corpus

We have so far concentrated on ingesting into the OpenCitations Corpus bibliographic references from open access papers available at PubMed Central, the encoding of these data in RDF, and high-quality curation of the citation links they represent, involving metadata enrichment from the Crossref API and (for authors) the ORCID API.

To date (19th February 2018), the OCC has ingested the references from 302,758 citing bibliographic resources, and contains information about 12,830,347 citation links to 6,549,665 cited resources. Plans to expand the coverage of the OCC are outlined below.

User interfaces

The information within the OCC can be accessed via OSCAR, our new generic OpenCitations RDF Search Application ( [1], which can be used for textual searches over any triplestore presenting a SPARQL endpoint.  Users can employ OSCAR to search the OCC for publication titles, author names, publication years, and identifiers (DOIs, PubMed IDs PubMed Central IDs, ORCIDs, and OCC corpus identifiers). Such a search returns details of all bibliographic resources within the OCC matching the search term, from which their references can be obtained, if known. In the near future, we will complement OSCAR with a browse interface named LUCINDA.

We also provide a SPARQL endpoint for directly querying the Blazegraph triplestore in which we store the OCC RDF, and we plan in the near future to supplement such programmatic access with a REST API.  In addition, the contents of the entire triplestore, and of the various sub-databases within the Corpus, together with their provenance information, are downloadable from Figshare as monthly dumps.  Once the REST API has been developed, we will turn our attention to developing user interfaces for the interactive visualization of citation graphs.

The OpenCitations Data Model

As described in the previous blog post, we have just completed a comprehensive revision of the OpenCitations Data Model (OCDM, available at, which we use to capture descriptions of all aspects of the OCC citations and their provenance. This model makes extensive use of our SPAR (Semantic Publishing and Referencing) Ontologies (, which we developed to describe all aspects of the scholarly publishing domain in RDF .

The OpenCitations Data Model is freely available for third parties to use when recording their own bibliographic and citation information in RDF, with the advantage that data so modelled will be immediately compatible with those within the OpenCitations Corpus, which can act as a publishing venue for such third-party data.

Future ingest rate and data sources

Since July 2016, the instantiation of the OpenCitations Corpus currently running at the University of Bologna has been ingesting reference lists from biomedical journal articles at the relatively slow rate of about 200,000 citing bibliographic resources per year. During February 2018, ingestion into the Corpus is suspended, while we move the system to a completely new and more powerful server, supplemented by thirty Raspberry Pi ingest engines that will work in parallel feeding ingested data to the server.

This will increase our ingestion rate ~30-fold to about six million citing bibliographic resources per year, equivalent to ~240 million citations per year at 40 references per paper (the current OCC value is 42.4 references per paper).  We should then be able to complete ingestion of the ~1.4 million remaining OA resources at PubMed Central within about three months.

At that stage, we plan to start ingesting references from the ~17 million journal articles whose deposited references are now open at Crossref as a consequence of the Initiative for Open Citations.  The scholarly world currently publishes about 2.5 million new journal articles each year, of which about half will be probably be open at Crossref (assuming Elsevier has not by then opened its references).  So, by the end of 2020, Crossref will have ~650 million open references.  In addition to ingesting new open Crossref references as they are made available, we will be able to eat into the backlog of existing Crossref open references at a catch-up rate of ~190 million per year.  By the end of 2020, we anticipate that the OCC should contain ~650 million citations harvested from PMC and Crossref, roughly half the coverage of Web of Science.  We are currently also considering ingest of references from other major bibliographic databases.

Our vision for OpenCitations

Our vision is that OpenCitations should become a comprehensive source of open citation information from all disciplines of scholarly endeavour encoded as Linked Open Data, a key component of the academic open infrastructure used on a daily basis without charge by scholars worldwide.

To be of maximum utility, it requires effective graphical user interfaces and analytical tools to interrogate and quantify the data contained within the OCC.  Since these data are all open, we anticipate that such interface and tool development will best be undertaken collaboratively within the open scholarly community, and we invite developers interested in such collaboration to contact us at


[1]     Ivan Heibi, Silvio Peroni and David Shotton (2018).  OSCAR: A customisable tool for free-text search over SPARQL endpoints. Accepted to the 2018 International Workshop on Semantics, Analytics, Visualisation: Enhancing Scholarly Dissemination Workshop (, co-located with The Web Conference), 24 April 2018 – Lyon, France.  Preprint available at

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