Five reasons why 2021 has been a great year for OpenCitations

2021 is just behind us. Since January is “the Monday of the months”, as F. Scott Fitzgerald once wrote[1], it’s a good time to take stock of what happened at OpenCitations during the past year.

Among the numerous events, achievements and challenges that 2021 brought with it, we want to highlight five milestones which make us proud to look back:

1. We extended our coverage to well over one billion citations

During 2021, OpenCitations’ largest index COCI (the OpenCitations Index of Crossref open DOI-to-DOI citations) was able to include for the first time the citation links involving references that had been opened at Crossref by Elsevier and the American Chemical Society, thereby greatly expanding its coverage. The last release of COCI (November 2021) is based on open references to works with DOIs within the Crossref dump dated October 2021, and, as a result, COCI now contains information on more than 1.23 billion citations involving almost 70 million publications.
A recent analysis by Alberto Martìn-Martìn (Facultad de Comunicación y Documentación, Universidad de Granada, Spain), published on the OpenCitations Blog in October, shows that the citation coverage provided by OpenCitations is approaching parity with that of the leading commercial citation indexes, Web of Science and Scopus, offering a viable alternative upon which to base open and reproducible metrics of academic performance.

2. OpenCitations team grew

Last summer, we appointed Claudio Fabbri as our Administrator and Research Manager to take responsibility for the day-to-day administrative and financial activities of OpenCitations; Chiara Di Giambattista as Communications Director and Community Development Manager to take care of all communications and community interactions made on behalf of OpenCitations; and Giuseppe Grieco as our new Software and Systems Developer to take charge of technical development related to the OpenCitations services.

Thanks to the support from the OpenAIRE Nexus project, the team has also recently welcomed Arcangelo Massari as our new Software Developer to take care of the development of the new database OpenCitations Meta. We anticipate further appointments during 2022!

Our International Advisory Board met in November, and we thank its members for the valuable advice they provided. The Board will meet again later this month.

3. We participated in many international meetings

During the past year, OpenCitations’ directors Silvio Peroni and David Shotton took part in numerous international conferences, webinars and workshops, including the LIBER Annual Conference 2021, the OS Fair 2021, OASPA 2021 and FORCE2021. These provided excellent opportunities to describe and promote OpenCitations, to reach out to new potential stakeholders, and to discuss with other experts the main themes of our activities and plans as they relate to Open Science.

The year ended with a bang, with the announcement during the closing session of FORCE2021 that the 2021 Open Publishing Award for Open Data had been awarded to OpenCitations.

4. We received a world of support

In 2021, thanks to our involvement in the SCOSS funding campaign and to our commitment to reaching out to the libraries and universities potentially interested in OpenCitations, we gathered a wide international community of stakeholders and supporters around us. We are deeply thankful to the 6 consortia and 56 institutions across the globe which are now supporting us financially, thus making it possible for us to enhance our services and expand our team. You can find the full list of our supporters on the OpenCitations website and in this recent Thank You video:

Additionally, in January 2021, we started our involvement in the EC-funded OpenAIRE Nexus project, bringing us into closer collaboration with our European colleagues and infrastructures, including OpenAIRE. The main aim of the project is to create a framework of services for assisting in publishing research, monitoring its impact, helping promote its discovery, and integrating it into the European Open Science Cloud (EOSC) “for the benefit of the open science community worldwide”. In OpenCitations, we’re thrilled to be part of this collaborative project by providing open bibliographic citations as part of the open data components of OpenAIRE and the EOSC.

5. We set the stage for future developments

Thanks to the research grants and the support and endorsement we have received from the international scholarly community, we are now working on a variety of new services, thus setting our goals for the coming years. In particular, we want to enhance OpenCitations partnerships and dialogue with the scholarly community; to collaborate with colleagues to develop new services that will expand our citation coverage, including new OpenCitations indexes of NIH-OCC, of DataCite and of other sources of open references, that will all be searchable through a single API; and to create OpenCitations Meta, our new database that will hold comprehensive bibliographic metadata of the publications involved in our indexes citations, thereby enabling faster query responses and the ability to host citations involving publications lacking DOIs[2].

[1] F. Scott Fitzgerald (2002). The beautiful and damned (page 50 in the original 1922 edition); United Kingdom: Dover Publications. https://www.google.it/books/edition/The_Beautiful_and_Damned/-tUoAwAAQBAJ?hl=en&gbpv=0

[2] Silvio Peroni, David Shotton; OpenCitations, an infrastructure organization for open scholarship. Quantitative Science Studies 2020; 1 (1): 428–444. doi: https://doi.org/10.1162/qss_a_00023

Reflections on the global citation graph

In his call for open citations, Dario Taraborelli hailed the scholarly citation graph (in which the nodes (vertices) are individual academic publications and the links (edges) represent bibliographic citations from one publication to another) as one of humankind’s most important intellectual achievements.

We all understand that the inclusion within our own academic publications of bibliographic references to the works of others is one of the most explicit ways of acknowledging the thoughts, discoveries, achievements and influences of other scholars, and their contributions to our own work. Not only does what we gain from their publications enable us to make intellectual progress, by “standing on the shoulders of giants” as Newton once famously observed [1], but the influence of these publications extends forward in time across the entire intellectual landscape, like gigantic shadows cast at sunset, whether or not those influenced by these publications have occasion to reference them in their own works.

A bibliographic citation is not only “a conceptual directional link from a citing entity to a cited entity, created by a human performative act of making a citation”, but it is additionally both enduring and retrospective. Enduring, because once made it persists for ever within the global corpus of scholarly literature, and retrospective because (with the exception of occasional contemporaneous citations) the cited publication predates the citing publication.

At the anterior margin of a crawling cell, cellular protrusive extension (for example of a pseudopodium) is achieved by the catalysed polymerization of new filaments of the cytoskeletal protein actin from attachment sites on an existing stationary actin filament network, pushing the cell margin forward [2]. The scholarly citation network (or citation graph, the two terms here being used interchangeably) is similarly dynamic and temporally directional, being extended forward as new works of scholarship are published. Extension of knowledge is achieved by the catalytic inspiration provided by existing academic publications, themselves temporally stationary within the expanding citation network, leading to the publication of new works of scholarship that cite these previous publications and thus extend the citation network further into the future. The citation graph is thus not just an acyclic directed graph, but an acyclic temporally directed graph. Indeed, it is this temporal aspect of the citation network that is one of its most important features.

To use another analogy, the human genealogical tree is inherently multidimensional and difficult to represent pictorially in its entirety, because each new birth brings together the family trees of the child’s two parents. However, unless the parents are seriously promiscuous, the resulting genealogical tree is not impossibly complex. In contrast, the scholarly citation network is much more highly interlinked, since each new publication cites not just two but many preceding (‘parent’) publications, which themselves may beget many other citations.

Visualization of the global scholarly citation graph, or portions of it, is thus inherently difficult, and the important temporal aspect of the graph is the one ignored by almost every method used for visualizing aspects of that graph. Existing methods may take the broad view, showing the links, and the strength of those links, between one scholarly domain and another, thus visualizing the ‘structure of science’. Alternatively, they may take a more detailed view of a small section of the graph, visualize the proximity of individual publications to one another. Often a radial display is chosen for this, that shows in closest proximity those papers directly referenced by the selected publication in the centre, then at a greater radius those papers referenced by the cited papers shown in the inner circle, and so on. Because of the graph’s complexity, such displays quickly looses intelligibility after two citation links.

Among a small number of visualization applications that do not ignore the temporal aspect of the graph is Citeology, a temporally based citation network visualization tool developed some years ago by Justin Matejka and colleagues at the design software company Autodesk [3]. Unfortunately, this innovative software prototype was not central to that company’s mission, development ceased, and the Citeology Java app is no longer available. However, in his last email to me, Justin Matejka kindly offered to help others re-create this application.

There is thus an urgent need for innovative new open-source visualization tools that will clearly and dynamically display portions of the global citation graph, for example the direct and indirect citation connections between any two publications or any two individuals, along the temporal axis of publication date. Developers within the open science community please step forward!

References

[1] Isaac Newton, in a 1675 letter to Robert Hooke, wrote “If I have seen further it is by standing on the shoulders of Giants.” https://discover.hsp.org/Record/dc-9792/

[2] Bruce Alberts et al. (2014). Molecular Biology of the Cell. 6th Edition. Garland Science. Chapter 16, The Cytoskeleton.

[3] Justin Matejka, Tovi Grossman, George Fitzmaurice (2012). Citeology: Visualizing Paper Genealogy. ACM Extended Abstracts on Human Factors in Computing Systems. https://www.autodesk.com/research/publications/citeology https://d2f99xq7vri1nk.cloudfront.net/CiteologyVideo.mp4

Querying the OpenCitations Corpus

OpenCitations makes available a SPARQL endpoint for querying the data included in the OpenCitations Corpus. While several queries are possible according to the model described in the website (and, with more details, in the official metadata document of the Corpus), we have received some requests by users of the service for exemplar queries. We have chosen two of them, which are particularly relevant with regard to the work that has been done in the past months by the Initiative for Open Citations – that we have already introduced in another blog post.

Query: return all the papers (including their titles) citing the article with DOI “10.1038/227680a0”.

PREFIX cito: <http://purl.org/spar/cito/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX datacite: <http://purl.org/spar/datacite/>
PREFIX literal: <http://www.essepuntato.it/2010/06/literalreification/>
SELECT ?citing ?title WHERE {
  ?id a datacite:Identifier ;
    datacite:usesIdentifierScheme datacite:doi ;
    literal:hasLiteralValue "10.1038/227680a0" .
  ?br 
    datacite:hasIdentifier ?id ;
    ^cito:cites ?citing .
  ?citing dcterms:title ?title
}

Query: return all the papers cited by the bibliographic resource “br/4186” included in the OCC, including the text of bibliographic references used in “br/4186” for making the citations and the titles of the cited papers.

PREFIX cito: <http://purl.org/spar/cito/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX biro: <http://purl.org/spar/biro/>
PREFIX frbr: <http://purl.org/vocab/frbr/core#>
PREFIX c4o: <http://purl.org/spar/c4o/>
SELECT ?cited ?cited_ref ?title WHERE {
  <https://w3id.org/oc/corpus/br/4186> cito:cites ?cited .
  OPTIONAL { 
    <https://w3id.org/oc/corpus/br/4186> frbr:part ?ref .
    ?ref biro:references ?cited ;
      c4o:hasContent ?cited_ref 
  }
  OPTIONAL { ?cited dcterms:title ?title }
}

Open Citations is dead. Long live OpenCitations.

OpenCitations logo 50% with words greyBG

In October 2015, I asked Silvio Peroni, my long-term colleague in the development of the SPAR Ontologies, to become Co-Director of the Open Citations Project, and to work with me in taking forward the prototype Open Citations Corpus (OCC), originally developed at the University of Oxford with the support of Jisc, with the aim of developing it into a production service of real use to scholars.

The result is OpenCitations, a new instantiation of the OCC hosted by the Department of Computer Science and Engineering of the University of Bologna, based on a new metadata schema and employing several new technologies to automate the ingestion of fresh citation metadata from authoritative sources.

Since the beginning of July 2016, OpenCitations has been ingesting and processing accurate bibliographic references harvested from the reference lists of scholarly papers available in Europe PubMed Central, enriched by metadata from Crossref. These scholarly citation data are described using the SPAR Ontologies according to the new OpenCitations metadata document [1], and are published under a Creative Commons public domain dedication (CC0), so that others may freely build upon, enhance and reuse them for any purpose, without restriction under copyright or database law. We have described the new OpenCitations Corpus, and the new software developed by Silvio to create it, in [2].

OpenCitations is being continuously populated from the scholarly literature, and, as of 30th March 2017, has ingested the references from 123,989 citing bibliographic resources, and contains information about 5,307,857 citation links to 3,469,648 cited resources.

The whole OCC is now available for querying (via SPARQL), and for browsing by means of a very simple Web interface that shows only the data about bibliographic entities (e.g. https://w3id.org/oc/corpus/br/1). Additional more user-friendly interfaces will be available in the coming months. The entire contents of the OpenCitations Corpus (OCC) are also archived every month as data dumps that are made available online through Figshare. Each dump comprises several zip archives, each containing either data or provenance information of a particular sub-dataset of the OCC.

Despite the fact that OpenCitations presently contains only a small proportion of global citation data, it is important to realize that, because of the very nature of scholarly citation, even this partial coverage includes citations of the most important papers in every biomedical field, these critical papers being characterized by the high number of their inward citation links.

[1] Silvio Peroni, David Shotton (2016). Metadata for the OpenCitations Corpus. figshare. https://dx.doi.org/10.6084/m9.figshare.3443876

[2] Silvio Peroni, David Shotton, Fabio Vitali (2016). Freedom for bibliographic references: OpenCitations arise. Proceedings of 2016 International Workshop on Linked Data for Information Extraction (LD4IE 2016): 32-43.
https://w3id.org/oc/paper/occ-lisc2016.html

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