Presence of citations where the citing entity is the same as the cited entity

[eliarizzetto]

In OpenCitations Index, at least accessing the data via REST API, there are citations where the citing entity is the same as the cited entity. An example of such "circular" citations can be reproduced by querying the API for the citations towards the journal article with DOI 10.1093/beheco/arad018: https://opencitations.net/index/api/v2/citations/doi:10.1093/beheco/arad018.

The API response, posted here below, shows that the citing and cited entities share the same OMID (and the other available PIDs):
[ { oci: "061904012605-061904012605", cited: "omid:br/061904012605 doi:10.1093/beheco/arad018 openalex:W4362715641", author_sc: "yes", timespan: "P0Y0M0D", journal_sc: "yes", citing: "omid:br/061904012605 doi:10.1093/beheco/arad018 openalex:W4362715641", creation: "2023-04-08" } ]

As concerns this specific example, the issue seems to originate from an error in Crossref data, since the references of this publication's record erroneously list the publication itself: https://api.crossref.org/works/10.1093/beheco/arad018.

[eliarizzetto]

At the moment, there are 277,662 citations where the same entity is both the citing and the cited one. This count can be reproduced with the following query to the SPARQL endpoint (https://opencitations.net/index/sparql):

PREFIX cito: <http://purl.org/spar/cito/>

SELECT (COUNT(?citation) as ?citationCount)
WHERE {
  ?citation a cito:Citation ;
      cito:hasCitingEntity ?entity ;
      cito:hasCitedEntity ?entity .
}