Citation Typing Ontology (CiTO)

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Peroni, S., Shotton, D. (2012). FaBiO and CiTO: ontologies for describing bibliographic resources and citations. In Journal of Web Semantics: Science, Services and Agents on the World Wide Web, 17 (December 2012): 33-43. Amsterdam, The Netherlands: Elsevier. Open Access at:

**CiTO**, **the Citation Typing Ontology**, makes it possible for authors (or others) to mark citation links and to capture their citation *intent* (e.g., ``cito:extends``, ``cito:usesMethodIn``, ``cito:supports``) when someone cites a particular publication. In particular, CiTO allows one to create metadata describing citations that are distinct from metadata describing the cited works themselves, and permits the motives of an author when referring to another document to be captured. CiTO contains just two main object properties, ``cito:cites`` and its inverse ``cito:isCitedBy``, each of which has forty-one sub-properties, plus four additional generic object properties – i.e. ``cito:shareAuthorsWith``, ``cito:sharesAuthorInstitutionWith``, ``cito:sharesFundingAgencyWith`` and ``cito:likes`` – that may be used even outside a citation act. As defined in [Functions of Citations Ontology](/ontologies/foco), all these properties (and, consequently, their inverses) may be classified as rhetorical and/or factual, with the rhetorical properties being grouped in three sets depending on their connotation: positive, informative (or neutral) or negative. Note that all the domain and range constraints from the object properties are not defined, so that this ontology could be easily integrated with other models, e.g., [FaBiO](/ontologies/fabio). CiTO makes available a mechanism that permits the citation itself (i.e., the *citation act*) to be reified, so that it can become the subject or object of other RDF statements. In particular, the reifying class is ``cito:CitationAct``, and its accompanying object properties, i.e., ``cito:hasCitingEntity``, ``cito:hasCitationCharacterization`` and ``cito:hasCitedEntity``, can be employed to reify direct citation act statements made using the CiTO citation object property ``cito:cites`` or one of its sub-properties. In addition, two other ontologies have been defined for explicitly describing specific aspects of CiTO, i.e.: * the [Functions of Citations Ontology (FOCO)]( that provides a classification for all the CiTO properties according to their factual and positive/neutral/negative rhetorical functions; * the [CiTO to Wordnet Ontology (C2W)]( that maps all the CiTO properties defining citations with the appropriate Wordnet synsets (as defined in their RDF formalisation).</p></li>

Examples of use of CiTO

  1. Defining citation links and their functions
  2. Annotating a citation act with an additional text-defined citation function
  3. Annotating an in-text reference pointer with a citation function

Defining citation links and their functions

CiTO allows one to link two papers – or, more generally, two generic resources – where one (i.e., the citing paper) cites another one (i.e., the cited paper) according to a particular citation function (e.g., ``cito:extends``, ``cito:usesMethodIn``, ``cito:supports``). CiTO makes available two different approaches for creating such links. In the direct approach, we can use any of the CiTO properties as predicate of statements for defining citation acts. In the reified approach, we can define the citation act as a proper individual of the class ``cito:CitationAct``, in order to use it as subject/object of other statements.

@prefix : <> .
@prefix cito: <> .

# Direct form for a citation
:paper-a cito:extends :paper-b .

# Reified form for a citation sharing the same
# citation function of the above one
:citation a cito:CitationAct ;
    cito:hasCitingEntity :paper-a ;
    cito:hasCitationCharacterization cito:extends ;
    cito:hasCitedEntity :paper-b .

Please cite the source above with the following reference:

Peroni, Silvio (2015): Example of use of CiTO #1. figshare.

Annotating a citation act with an additional text-defined citation function

Despite the extensive list of CiTO properties, there could be situations in which the purpose of making a citation cannot be adequately expressed using these CiTO properties. It is now possible to use the [Open Annotation Data Model]( to define the reason for, or the nature of, the citation. In the [Open Annotation Data Model Ontology](, an annotation is described as a member of the class ``oa:Annotation``, which has a body containing the annotation itself defined by ``oa:hasBody``, and an annotation target (the thing to which the annotation relates) defined by ``oa:hasTarget``. In order to express a more precise justification of a citation act, the target of the annotation should be an individual of the class ``cito:CitationAct``, while the body, i.e. the textual content of the annotation itself, is described using the [W3C Content Vocabulary]( as an individual of the class ``cnt:ContentAsText``, which the property ``cnt:chars`` relates to the text string actually providing the annotation. In addition, an OA annotation can be further characterized by the motivation for making such annotation, defined by ``oa:motivatedBy``. In this case, the appropriate motivation is ``oa:commenting``, an instance of the class ``oa:Motivation``. The whole example has been extracted from the blog post ["Extending CiTO to enable use of the Open Annotation Data Model to describe citations"](

@prefix : <> .
@prefix cito: <> .
@prefix cnt: <> .
@prefix oa: <> .

:annotation a oa:Annotation;
    oa:motivatedBy oa:commenting ;
    oa:hasBody :comment ;
    oa:hasTarget :citation-act .

:comment a cnt:ContentAsText ;
    cnt:chars "I'm citing that paper because it
        initiated this whole new field of research." .

:citation-act a cito:CitationAct;
    cito:hasCitingEntity :paper-a ;
    cito:hasCitationCharacterization cito:cites ;
    cito:hasCitedEntity :paper-b .

Please cite the source above with the following reference:

Peroni, Silvio (2015): Example of use of CiTO #2. figshare.

Annotating an in-text reference pointer with a citation function

Several citations to the same article could exist in the same text, and such citations could express different functions depending on the author's view. Usually, in a scientific paper, each of these citations is actually described by means of an *in-text reference pointers*, i.e., a textual device (e.g., "[6]") denoting a single bibliographic reference (referring to the cited paper) that is embedded in the text of a document within the context of a particular sentence. One of the SPAR Ontologies, i.e., [C4O](/ontologies/c4o), defines the entities for describing in-text reference pointers (individuals of the class ``c4o:InTextReferencePointer``) and to link them to the related bibliographic references included in the paper. The [Open Annotation Data Model Ontology]( can be used to annotate each in-text reference pointer of a paper with the particular citation act it conveys. In particular, we can create an annotation (i.e., an individual of the class ``oa:Annotation``) with a body (object property ``oa:hasBody``) containing a specific citation act among the citing paper and the cited paper, and with the in-text reference pointer as target (object property ``oa:hasTarget``) of the annotation. In addition, it is also possible to specify (through the object property ``oa:annotatedBy``) the agent who created such annotation – who can be the author of the paper containing the in-text reference pointer, a reader or a software agent.

@prefix : <> .
@prefix cito: <> .
@prefix c4o: <> .
@prefix oa: <> .
@prefix per: <> .

:annotation a oa:Annotation ;
    oa:hasBody :citation-act ;
    oa:hasTarget :in-text-ref-pointer ;
    oa:annotatedBy per:silvio-peroni .

:citation-act a cito:CitationAct;
    cito:hasCitingEntity :paper-a ;
    cito:hasCitationEvent cito:extends ;
    cito:hasCitedEntity :paper-b .

:in-text-ref-pointer a c4o:InTextReferencePointer ;
    c4o:hasContent "[6]" .

Please cite the source above with the following reference:

Peroni, Silvio (2015): Example of use of CiTO #3. figshare.