The open citations revolution

Citations are the primary tool to acknowledge others' prior work on a particular topic. They enable one to find key publications within a particular field, and are used also for research purposes – e.g. people working in Bibliometrics, Informetrics, and Scientometrics use them for analysing the complex relationships that exist within huge networks of citations of scholarly works. In addition, citation data are important for the assessment of the quality of research by means of metrics and indicators calculated from citation databases. However, the cruel reality is that citations have been locked up in close silos for years, and often they can only be accessed by paying significant subscription fees.

But the scenario is quickly changing. In the past years, several initiatives (I4OC, OpenCitations, WikiCite, Springer Nature SciGraph, LORC, etc.) have started to promote the availability of open citation data. In this talk I will introduce some of the main significative efforts in the area, focussing on the way Semantic Publishing technologies have been used and adopted for enabling a FAIR publication of open citation data.

To cite

Oxford dictionary: refer to (a passage, book, or author) as evidence for or justification of an argument or statement, especially in a scholarly work

Isaac Newton (1675): If I have seen further, it is by standing on the shoulders of giants

Citations are unanimously recognised as crucial for knitting together our scientific and cultural knowledge

References and citations

Everything is a reference

Semantic overload!

A citation is a conceptual directional link from a citing entity to a cited entity

Kinds of citations

Citations instantiated by the inclusion of a bibliographic reference (1) are different from those defined by an in-text reference pointer + citation context (2)

  1. Generate a plain citation link

  2. Generate a citation link with a specific citation function

Plain citations: current status

A citation index is an index of (plain) citations between publications

  • Some are freely accessible but not downloadable, e.g. Google Scholar

  • The most authoritative by institutions worldwide, namely Scopus and Web of Science, can be accessed only by paying significant access fees

Usually are more oriented towards human readability rather than machine readability and data re-use

What about machine-readable open citation data?


The Initiative for Open Citations (I4OC, is a collaboration between scholarly publishers, researchers, and other interested parties to promote the unrestricted availability of scholarly citation data

Goal: promote the availability of data on citations that are:

  • structured - available in common and machine-readable formats

  • separable - no need to access the source bibliographic products

  • open - freely accessible and reusable

Pathway to open citations

Publishers deposit their reference data with Crossref, but the default state for the data is closed (i.e. not accessible through the Crossref REST API)

However one email is enough to make the data open

Challenge: persuade a group of influential publishers to release their data

What happened: before I4OC launch (6 April 2017), 1% of publications in Crossref with open references



49 scholarly publishers have opened their references, including the following major ones:

  • Commercial publishers - Association for Computing Machinery, BMJ, De Gruyter, eLife, EMBO Press, Hindawi, IOS Press, PeerJ, Pensoft Publishers, Portland Press, Public Library of Science, Springer Nature, Taylor & Francis, Wiley

  • University and scholarly presses - Cambridge University Press, Cold Spring Harbor Laboratory Press, Company of Biologists, Edinburgh University Press, MIT Press, Rockefeller University Press

  • Learned societies - American Association for the Advancement of Science (AAAS), American Physical Society, American Society for Cell Biology, International Union of Crystallography, Proceedings of the National Academy of Sciences (PNAS), Royal Society of Chemistry, The Royal Society

Founders and stakeholders

Crossref REST API

API call:

  "message": {
    "DOI": "10.1007/978-3-319-46547-0_18",
    "title": ["FOOD: FOod in Open Data"],
    "reference": [{
      "key": "18_CR1",
      "unstructured": "Falco, R., Gangemi, A., Peroni, S., Vitali, F.: Modelling OWL ontologies
                       with Graffoo. In: The Semantic Web: ESWC 2014 Satellite Events, pp. 320-325
      "DOI": "10.1007/978-3-319-11955-7_42",
      "doi-asserted-by": "crossref"
    }, {
      "key": "18_CR2",
      "unstructured": "Ferragina, P., Scaiella, U.: On-the-fly annotation of short text fragments
                       (by Wikipedia entities). In: Proceedings of the 19th ACM International
                       Conference on Information and Knowledge Management (CIKM 2010), pp.
                       1625-1628 (2010).",
      "DOI": "10.1145/1871437.1871689",
      "doi-asserted-by": "crossref"
    }, ... ],

FAIR data principles

FAIRness of citation data

Crossref citation data are not following all the FAIR data principles

  • F1: no persistent identifier is defined for metadata - just API URLs

  • I1: no use of formal language for knowledge representation - just JSON

  • I2: the vocabulary used in JSON is not FAIR

  • R1.2: only a bit of provenance, no change tracking

  • R1.3: use of specific JSON made for that purpose

While Crossref data are the main building block for FAIR open citation data, how can we reach FAIRness?


The OpenCitations Corpus (OCC, is a LOD repository of CC0 citation data

It provides >11M citation links from ~260,000 citing articles to ~6M cited resources + provenance information

Data accessible via HTTP URI (content negotiation), SPARQL endpoint, and monthly dumps (on Figshare)

Reuse of external APIs (Europe PubMed Central, Crossref, ORCID) and models (SPAR Ontologies)

More info: One year of the OpenCitations Corpus, talk on October 24, 2017, 10:50, room Stolz 2


WikiCite is an initiative to build a bibliographic database in Wikidata to serve all Wikimedia projects

Wikidata now includes 36M citation links using the cites (P2860) Property in Wikidata

All the data released in CC0

Additional tools built by the community, e.g. Scholia

Citation functions: what's up


When the citation links exist but are not described, the traveller through the city of scholarly publishing travels without specific directions, and will get lost in the maze of bridges that form the citation network

The Citation Typing Ontology (CiTO, enables characterization of the nature or type of citations, both factually (cito:usesMethodIn, cito:extends, etc.) and rhetorically (cito:agreesWith, cito:disputes, etc.)

Semantic Lancet

Semantic Lancet ( is a prototype focused on building LOD on scholarly publications

Its contains bibliographic data, abstract and citations


The Linked Open Research Cloud ( is a new project which makes available an inbox to receive Linked Data Notifications about scholarly communication resources

CC0 expected for notifications + provenance information

Notifications must meet the requirements of certain notification data shapes: article, annotations, citations

CiTO properties (i.e. subproperties of cito:cites) are suggested for specifying citation links

Journey to FAIR-I land

Key benefit for open citation data from I4OC home:

The creation of a public citation graph to explore connections between knowledge fields, and to follow the evolution of ideas and scholarly disciplines.

Having one single FAIR dataset with the complete citation graph of the whole scholarly literature is not feasible

Each initiative should provides its partial data and links its resources with those included within other citation datasets

Interlinking should be an additional mandatory I in FAIR if we want to reach a real public and global citation graph

Call for action

Authors and journal editors:

  • ask your publisher to free citation data

  • contribute actively to community initiatives with your citation data (e.g. share them in LORC)


  • join I4OC (

  • it is in the publisher's interests - better discoverability and use of its published content, both subscription access and open access

END The open citations revolution