Investigating Invalid DOIs in COCI - Protocol v4
Authors: Coppini Sara , Shahidzadeh Nooshin , Cioffi Alessia , Moretti Arianna 
Published: July 2021

A preliminary note This protocol illustrates the workflow adopted within a scholarly research that operates within the OpenCitations environment, which is an independent infrastructure organization for open scholarship dedicated to the publication of open bibliographic and citation data by the use of Semantic Web (Linked Data) technologies. COCI is the OpenCitations Index of Crossref open DOI-to-DOI citations. Purpose The primary purpose of this research is to find the publishers responsible for the missing citations in COCI (the OpenCitations Index of Crossref open DOI-to-DOI citations) by sending incorrect metadata to Crossref, the publishers to whom such invalid citations point to, and the number of previously invalid citations which are currently valid. Further, the additional aim of the present research is to provide material for future and deeper research on the same subject matter. In particular, we focus on keeping track of the main trends of evolution on the validity of citational data and on providing data to facilitate publishers' identification. Study design/methodology In order to study the invalid citations, we use an already generated CSV file which is available online, containing - for each citation - the valid citing DOI and the invalid cited DOI. First of all, through a DOI API request we check whether the validity state of the cited DOI has changed, and then we use DOI's prefix for a CROSSREF API request, in order to identify the responsible and referenced publishers. Findings For each individual publisher, we retrieve the number of incorrect given citations metadata sent, and the number of invalid citations received, to which we decided to add the information about the number of addressed and received citations validated with the software we developed, and its list of prefixes. We also extract the total number of invalid citations that have since been corrected. Any further material provided as result of this research, such as the lists of validated and still invalid citations, is meant to incentivize future improvements of the studies on this field. Originality/value The results of this research may point us to publishers who generally send out incorrect citation metadata and, inversely, those who generally receive invalid citations. These findings can first of all raise awareness of the accuracy of certain publishing houses in managing their metadata (or lack thereof). Moreover, finding these trends and showcasing the labor of the corrections may lead to increasingly valid citations if the proper measures are taken. Research limitations/implications Based on the available data for COCI, there may be a slight bias in our sample, causing some publishers to be incorrectly represented. Minimal bibliography on related projects Heibi, I., Peroni, S. & Shotton, D. Software review: COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations.Scientometrics 121, 1213–1228 (2019). https://doi.org/10.1007/s11192-019-03217-6. Silvio Peroni, David Shotton (2020). OpenCitations, an infrastructure organization for open scholarship. Quantitative Science Studies, 1(1): 428-444. https://doi.org/10.1162/qss_a_00023. Peroni, S. (2021). Citations to invalid DOI-identified entities obtained from processing DOI-to-DOI citations to add in COCI (1.0). Zenodo. https://doi.org/10.5281/ZENODO.4625300. Related Diagrams In order to improve readability and reusability of our protocol, we provide here the flow diagram representing the steps of the procedure and an image of a simplified explicative scheme of the related software structure .