Persistent Identifiers of Digital and Non-digital Objects
Persistent identifiers (PIDs) are unique and lasting hyperlinks leading to various digital objects (e.g., scientific publications, research data, registered reports), non-digital objects (e.g., affiliations, projects, objects) and people. They usually consist of two parts:
- a unique identifier (unique identification code) that makes it possible to distinguish two related digital or non-digital entities (e.g., researchers with the same names using the ORCiD identifier),
- and a service that locates an entity over time, even if its location changes (e.g., a researcher changes institutions, a digital object moves to a website with a different domain), thus ensuring permanent findability of the entity.
When digital objects are submitted, trustworthy repositories assign one of the persistent identifiers to the metadata and the digital object. The allocation of persistent identifiers is one of the key properties by which we judge whether a repository is trustworthy or not.
Some repositories assign persistent identifiers to datasets and other digital objects by default (e.g., Zenodo, Dryad, Mendeley Data), whereas others do so at the request of users (e.g., Figshare, 4TU.ResearchData, Social Science Data Archives). The way this is usually done in the second case is that the authors submitting the data or other files manually reserve a permanent identifier for them. CTK UL recommends that you use this option if the repository offers it to make your files more easily findable.
Persistent Identifiers of Digital Objects
The most important persistent identifiers for digital objects are (adapted from the Digital Preservation Handbook):
Digital Object Identifier (DOI)
Digital Object Identifier is a persistent identifier for digital and non-digital objects that can be established by member organizations of one of the DOI Registration Agencies. The best-known examples are CrossRef for scientific papers and some other types of scientific publications, and DataCite for various types of data objects. In addition to being a unique identifier, a DOI also has a system infrastructure to ensure that a URL resolves to the correct location of the object it designates.
DOIs are assigned to data sets by general repositories such as Zenodo, Dryad, Figshare, OSF, Harvard Dataverse and Mendeley Data, some institutional repositories (e.g., 4TU.ResearchData) and trustworthy domain-specific repositories (e.g., Slovenian Social Science Data Archives).
Handle is a persistent identifier for online resources managed by the American non-profit organization Corporation for National Research Initiatives. Handle resolves URLs to the object's current location using a central registry. Each Handle identifies one resource and the organization that created or currently maintains that resource. It does not encode any information about the resource, but only allows the retrieval of metadata about that resource. Handle is based on the technical infrastructure of DOIs, which are a subcategory of Handle identifiers.
In Slovenia, Handle is used by the DiRROS repository.
Universal Resource Name (URN)
The Universal Resource Name is the product of the work of the Internet Engineering Task Force. URN was designed to be compatible with existing systems of standard identifiers, such as ISSN. Therefore, it defines system-specific namespaces instead of namespaces specific to the organisation that grants permanent identifiers (as in the case of DOIs). The use of URNs is being abandoned these days.
Archival Resource Key (ARK)
The Archival Resource Key is a persistent identifier for digital and non-digital objects designed by the California Digital Library. ARK is primarily used by libraries, data centers, archives, museums, publishing houses and government agencies (a full list is available on the service's website). It is similar to identifiers of the DOI, Handle and URN types, but is cheaper, more flexible and less centralized. Among other things, ARK enables:
- creating an unlimited number of persistent identifiers without paying for the right to do so,
- adding any number of metadata (or none) to the objects it links to,
- creating links directly to the objects without first redirecting the visitor to a landing page,
- resolving millions of ARKs by managing just one ARK via a suffix passthrough.
A notable service that uses ARK-type identifiers is the Portico digital science archive.
Persistent Uniform Resource Locator (PURL)
Persistent Uniform Resource Locator is a URL that redirects to the location of the requested web resource using standard HTTPS status codes. A PURL is thus a permanent web address that contains a command to redirect to another, potentially changeable web page.
Persistent Identifiers of Non-digital Objects
The DOI and ARK type identifiers can also be used for non-digital objects. The Smithsonian Museum thus uses the ARK identifier for museum specimens, and the Louvre Museum for works of art. But there are also permanent identifiers dedicated to only non-digital objects or even persons. The most famous of them is certainly the International Standard Book Number (ISBN), a permanent identifier for books.
For researchers, the most relevant identifiers for identifying authors are:
- International Standard Name Identifier (ISNI),
- Open Researcher and Contributor Identifier (ORCID iD),
- Scopus Author ID.
There are also identifiers to indicate institutional affiliations and research funders:
In addition, permanent identifiers for research samples, materials and instruments are also useful:
- International Generic Sample Number (IGSN) for physical samples and specimens,
- Research Resource Identifier (RRID) for laboratory material in biomedicine (e.g., plasmids, cells, antibodies, organisms),
- Persistent Identifier of Instruments (PIDINST) for measurement instruments.
Last update: 30 August 2022