CiTO, the Citation Typing Ontology

Abstract

CiTO, the Citation Typing Ontology, is an ontology for describing the nature of reference citations in scientific research articles and other scholarly works, both to other such publications and also to Web information resources, and for publishing these descriptions on the Semantic Web. Citation are described in terms of the factual and rhetorical relationships between citing publication and cited publication, the in-text and global citation frequencies of each cited work, and the nature of the cited work itself, including its publication and peer review status. This paper describes CiTO and illustrates its usefulness both for the annotation of bibliographic reference lists and for the visualization of citation networks. The latest version of CiTO, which this paper describes, is CiTO Version 1.6, published on 19 March 2010. CiTO is written in the Web Ontology Language OWL, uses the namespace http://purl.org/net/cito/, and is available from http://purl.org/net/cito/. This site uses content negotiation to deliver to the user an OWLDoc Web version of the ontology if accessed via a Web browser, or the OWL ontology itself if accessed from an ontology management tool such as Protégé 4 (http://protege.stanford.edu/). Collaborative work is currently under way to harmonize CiTO with other ontologies describing bibliographies and the rhetorical structure of scientific discourse.

Figure 1

A CiTO citation network A citation network of selected articles directly or indirectly cited by Reis et al. (2008) [4], automatically displayed using the open source RDF graphing application Welkin, from an input RDF graph of cito:cites relationships.

Figure 2

An alternative representation of a CiTO citation network, displaying both in-text and global citation frequencies This figure shows the same citation network as Figure 1, but was created manually to encode citation frequency information. The node size of each pre-2006 reference is proportional to the cube root of the number of global citations received, using numerical data from Google Scholar acquired on March 11 2009. The bumps on each citing reference are proportional to the square root of the number of in-text citations of the cited paper within each citing paper, an indication of the importance of the cited paper to the citing paper, and have a colour that matches the colour of the cited paper.

Figure 3

The FRBR classification The diagram shows the relationships between Works, Expressions, Manifestations and Copies, and their relationship to people and/or corporate bodies in the FRBR classification.

Figure 4

The CiTO Ontology A screenshot of the ontology editor Protégé 4, showing the upper-level classes and object properties of CiTO, and the relationship of these classes with the corresponding FRBR classes.

Figure 5

An example of the use of CiTO to annotate a reference list The first three references from the reference list of the enhance version of Reis et al. (2008) [4], with the citation typing display turned on. Above the references are buttons to re-order the references, and to turn off the citation typing display. This figure was first published in Shotton et al. [6].