Table 1. Commonly used PIDs in research workflows.

Outputs:     • Digital object identifier (DOI): permanent URL (uniform resource locator) or hyperlink that will always lead users to the resource, even if its home webpage is renamed or changes.     • NCBI accession numbers: unique identifiers for sequence records [20].

People:     • ORCID ID: Per their website, ORCID is “an international, interdisciplinary, open, nonproprietary, and not-for-profit organization created by the research community for the benefit of all stakeholders, including you and the organizations that support the research ecosystem” [21]. Individuals who sign up with ORCID receive an http URI with 16 digits that uniquely identifies them. Appending this URI, or PID, to research outputs will help with citation counts and other metrics.

Concepts (examples):     • Medical Subject Headings (MeSH): subject terms with associated PIDs for biomedical concepts [22].     • UniProt names and taxonomy section: provides information about protein and gene names, as well as the organism that is the source of the protein sequence [23].     • Other unique persistent identifiers, such as those outlined in the PID Graph [24].