The Basics
Benefits of PIDs
ORCID Services
ROR Services
DOI Services

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What are Persistent Identifiers?

Persistent Identifiers (PIDs) are globally unique, persistent, interoperable, and machine-readable/resolvable identifiers used to disambiguate entities providing a long-lasting reference to entities such as contributors, organizations, and objects. They are valuable assets in sharing information across systems for research, scholarship, and innovation; serving as a standard way to cite, reference, and track research.

What can get a PID?

PIDs can be assigned to elements throughout all parts of the research lifecycle, starting with the researcher, their award, the organization they are affiliated with, the instruments they use, all the way through to their final research outputs such as datasets and publications.

Types of Persistent Identifiers

Categories of Persistent Identifiers

Persistent identifiers are categorized by the type of content they disambiguate. There are 3 main types of PIDs:

PIDs for Work Products

Typically, digital object identifiers (DOIs) are used for work products or outputs
Used as a stable method for citation and discovery

PIDs for Individuals

The most notable of these PIDs is ORCID (Open Researcher and Contributor ID)
Used to disambiguate individuals

PIDs for Organizations

The most widely used PID for organizations is a Research Organization Registry ID (ROR)
Covers funders, employers, and research institutions

Alternative PIDs

Contributor
Organization
Object
Scientific Research PIDs
Library Centric
Services and Systems

In addition to ORCIDs, there are a number of other alternative options for personal identifiers, however many of these do not meet requirements established by governmental mandates and policies. These include:

arXiv
- Works to accurately identify and disambiguate all authors of all articles in arXiv.
- Since 2005, arXiv has used authority records that link user accounts with preprints.
- Since 2009, public author identifiers are offered once a user publishes their authored articles in arXiv for use in other services.
- arXiv allows users to link their ORCID iD with their arXiv authority records.
ResearcherID
- A Web of Science ResearcherID is a unique identifier that connects you to your publications across the Web of Science ecosystem (e.g., Web of Science, Publons, and InCites) and provides the global research community with an invaluable index to author information. Web of Science Group products (Web of Science, Publons, InCites, EndNote) use a Web of Science ResearcherID to match and disambiguate researchers across products.
- ResearcherID profiles can be connected with ORCID iD profiles.
Scopus Author ID
- Scopus Author IDs are automatically assigned to authors with works indexed in Elsevier’s Scopus abstract and citation database.
- Scopus Author IDs can be linked with ORCID iDs.
Google Scholar Profiles
- Provide a simple way for authors to showcase their academic publications. You can check who is citing your articles, graph citations over time, and compute several citation metrics. You can also make your profile public, so that it may appear in Google Scholar results when people search for your name, e.g., richard feynman.

*These identifiers do not meet the PID criteria established in the NSPM-33 memo defined by the Office of Science and Technology Policy (OSTP).

In addition to ORCIDs, there are a number of other alternative options for organizational identifiers, however many of these do not meet requirements established by governmental mandates and policies and/or may be proprietary. These include:

International Standard Name Identifier (ISNI)
- ISNI (ISO 27729) is an International Standards Organization (ISO) certified global standard number for identifying contributors and Organizations to creative works and those active in their distribution, including researchers, inventors, writers, publishers, and more. ISNIs disambiguate contributor and organization names to improve searching and discovery.
- ISNI identifiers, ORCID iDs, and RORs are interoperable.
Ringgold
- Are organizational identifiers used by publishers for disambiguation. It is underpinned by ISNI (International Standard Name Identifier) data.
- Ringolds require a paid subscription to monitor and update their identifiers.
Open Funder Registry
- Associates funding metadata with PIDs for grants and funding organizations.
- Funding metadata includes grant and/or salary awards, and loans and should include funder names (ORCIDs/RORs), funder IDs (OFRs), and associated grant numbers.

In addition to ORCIDs, there are a number of other alternative options for work product identifiers.These include:

Archival Resources Key (ARK)
- Is a URL identifier for an object that uses metadata to describe it using a registered Uniformed Resource Identifier (URI) scheme.
- ARKs are commonly used for the archiving of objects.
Handle (HNDL)
- Is a unique and persistent identifier registry for the identification and management of identifiers.
- Handle identifies a resource and the organization that maintains it.
Persistent Uniform Resource Locator (PURL)
- Is a URL that is a permanent web address that contains a command to redirect to the current location URL of a resource.
- PURLs redirects can change over time but a PURL will remain the same.
- PURLs are managed by the Internet Archive.
- ARKs, DOIs, and HNDLs are all forms of PURLs
Universal Resource Name (URN), Universal Resource Link (URL), and Universal Resource Identifier (URI)
- Is a persistent, location-independent identifier.
- URNs map namespace into a single URN. URIs are required to be globally unique and persistent even if a resource is no longer available.
- URNs are depreciated unless used as a formal namespace for a URI.
- URLs are unique addresses for resources on the internet such as web pages, images, videos, files, and more.
- URLs can change overtime and are not persistent.

Scientific Research PIDs are unique open identifiers for objects such as classification systems, life science, samples, species, projects, and others.

Scientific Research PIDs include:

International Generic Sample Number Organization (IGSN)
- IGSN is a globally unique and persistent identifier for material samples.
- Samples are a basic element for reference, study, and experimentation in many scientific disciplines, especially in
  - natural and environmental sciences
  - material sciences
  - agriculture
  - physical anthropology
  - archaeology
  - biomedicine
Life Science Identifiers (LSID)
- Life Science Identifiers were initially created to provide a protocol-independent identifier mechanism for the life sciences community.
- By using a URN (Uniform Resource Name) instead of a URL, a specific protocol (HTTP) is avoided.
- This is seen as an advantage because the identifier is much less likely to be invalidated by broken web links, but is also seen as a disadvantage because LSIDs cannot be resolved using basic HTTP resolution, and therefore cannot be resolved by most web browsers.
  - E.g., urn:lsid:example.org:specimen:12921
    urn:lsid:[authority]:[namespace]:[object id]
- LSIDs have a specification for assignment, structure and resolution.
- LSIDs can be generated and adopted by anyone willing to set up an LSID resolution service.
- Resolution requires a three-step process, including a DNS lookup, a call to retrieve a SOAP [SOAP] web service description document (WSDL [WSDL]), and a standard web resolution.
- LSIDs have been recommended by the biodiversity informatics community, but not to the exclusion of any other Persistent Identifier type.
- LSIDs may not be opaque due to the domain name and context name components and descriptive object identifiers.
- The authority portion is provided by the LSID domain name; the context is provided by the LSID namespace portion and the object identifier is provided by the object ID portion of the LSIDs
- LSIDs provide built-in versioning abilities.
- It is worth noting that these different types of Persistent Identifiers are not necessarily mutually exclusive. For example, an LSID could be represented as a URI using what is known as an “HTTP Proxy”, whereby the LSID is embedded within a URI, e.g., http://example.org/urn:lsid:example.org:specimen:12921.
Research Activity Identifier (RAiD)
- A RAiD captures project resourcing, inputs, and outputs including contributors, organizations, grants, instruments, publications, and datasets.
Resource Identification Portal (RRID)
- RRIDs, or Research Resource IDentifiers, are standard identifier numbers for research resources.
- RRIDs are a little different from the other PIDs in this list because they only apply to some research.
  - such as the exact equipment used for spectrometry or chromatography
  - custom biological agents like cell lines or antibodies
  - the version of software used; and so on.
- However, they cover a wide range of tools and resources and are growing.
- Fair Data Informatics lab: Scicrunch
- Scicrunch's "Registry" section aggregates a wide range of research resources and assigns RRIDs as well as showing other persistent IDs. It is the best one-stop place to search for resource identifiers to improve study reproducibility.
North American Industry Classification System (NAICS)
-  Is “the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy.” It was developed jointly across U.S. Canadian, and Mexican statistical organizations “to allow for a high level of comparability in business statistics among the North American countries."

Library Centric PIDs are unique open identifiers for library-specific uses such as books, organization names, and series naming.

Library Centric PIDs include:

International Standard Book Number (ISBN)
- The ISBN is a numeric book identifier which is intended to be unique.
- An ISBN is assigned to each separate edition and variation (except reprintings) of a publication.
  - For example, an ebook, a paperback and a hardcover edition of the same book will each have a different ISBN.
- The ISBN is ten digits long if assigned before 2007, and thirteen digits long if assigned on or after 1 January 2007.
  - Example: ISBN 978-92-9083-543-1 (paperback), ISBN 978-92-9083-544-8 (PDF)
Library of Congress Name Authority File (LCNAF)/ Name Authority Cooperative Program (NACO)
- Library of Congress authority records or Name Authority Files (NAFs) are created and contributed by the NACO program for authority files.
- Name authority files include personal, corporate, jurisdictional names, uniform titles, series, and subjects.
- You can search the Library of Congress authority records to determine the correct forms for names of persons, organizations, conferences, or titles.
Virtual International Authority File (VIAF)
- VIAFs combines multiple name authority files into a single name authority service.
- The goal of the service is to lower the cost and increase the utility of library authority files by matching and linking widely-used authority files and making that information available on the Web.
- VIAF has many contributors including ISNI, FAST Subjects, Library of Congress, and Wikidata.
Faceted Application of Subject Terminology (FAST)
- FAST (Faceted Application of Subject Terminology) is derived from the Library of Congress Subject Headings (LCSH), and is one of the library domains most widely used subject terminology schemas.
- FAST was developed in large part to meet the need for a general-use subject terminology scheme. The individual terms in the FAST vocabulary are divided into 9 categories/facets.
  - Personal names
  - Corporate names
  - Meeting names
  - Geographic names
  - Events
  - Titles
  - Time periods
  - Topics
  - Form/Genre
- FAST has evolved into a multi-faceted vocabulary with a universe of approximately 1.7 million headings across all facets. The facets are designed to be used together, but each may also be used independently.

Related services and systems are a key part for PIDs. The integration of PIDs in services and systems helps provide an exchange of information between services and systems and helps store information to reduce the administrative burden of re-entering the same information manually between multiple services and systems. The services and systems can include laboratory information management systems, repositories, research management systems, finance systems, human resources, and many others.

Related services and systems include:

Crossref
- Is a Digital Object Identifier Registration Agency.
DataCite
- Develops and supports methods to locate, identify and cite data and other research objects. It develops and supports the standards behind persistent identifiers for data, and the members assign them.
Dimensions
- Is an open comprehensive database that holds a wide range of research data. The database includes comprehensive collections of linked data to a single platform including grants, publications, datasets, and more.
Dryad
- Is a curated general-purpose repository that makes data discoverable, freely reusable, and citable.
- Most types of files can be submitted (e.g., text, spreadsheets, video, photographs, software code) including compressed archives of multiple files.
Figshare
- Is an open access data repository. Researchers can preserve their research outputs, such as datasets, images, and videos for access and discoverability.
- Figshare allows researchers to upload any file format and assigns a digital object identifier (DOI) for citations.
GeoNames
- Is a PID for geographic locations that are used with services and systems.
- GeoNames is integrated with ROR, ORCIDs, DataCite, CrossRef, OpenAlex and more.
Google Scholar Citations
- Allows authors to track citations of their articles via a profile linked to a Google account.
- The profile may be public or private, and users have the option to update their profile with new publications manually, automatically, or automatically with manual review.
INSPIRE
- is a trusted community hub that helps researchers to share and find accurate scholarly information in high-energy physics.
LinkedIn
- Uses internal identifiers for profile pages to solve the name ambiguity problem.
- ORCID iD can be added to LinkedIn profiles.
Mendeley Data
- Is an open research data repository, where researchers can store and share their data.
- Datasets uploaded to Mendeley Data go into a moderation process where they are reviewed. This ensures the content constitutes research data, is scientific, and does not contain a previously published research article.
OpenAlex
- Is a bibliographic catalog of scientific papers, authors, and institutions accessible in open access mode via APIs.
Open Science Framework
- Is a free, open-source research management and collaboration tool designed to help researchers document their project's lifecycle and archive materials.
- Each user, project, component, and file is given a unique, persistent uniform resource locator (URL) to enable sharing and promote attribution.
- Projects can also be assigned digital object identifiers (DOIs) if they are made publicly available.
ResearchGate
- Is a professional networking service for researchers.
- Users can share publications, track citations, and connect with other users.
- ResearchGate profiles may contain similar info to the other creator identifiers but have no claim to persistence or permanence.
- ORCIDs can be displayed on ResearchGate.
- However, there is no simple way to update publications between the two profiles.
Scopus
- Is a comprehensive, multidisciplinary abstract and citation database.
- Scopus uses linked data to discover authoritative research through metrics and analytical tools.
Web of Science
- Is a database that indexes articles from peer-reviewed journals.
- Allows researchers to search for publications, and citations and to track the impact of research.
Wikidata
- Is a free, collaborative database providing data supporting Wikipedia.
- The repository is primarily composed of items containing labels, aliases, and descriptive statements. Each item is assigned a unique identifier that is used throughout the Wikimedia ecosystem and beyond.
Zenodo
- Is an open repository for all scholarship, enabling researchers from all disciplines to share and preserve their research outputs, regardless of size or format. Free to upload and free to access, Zenodo makes scientific outputs of all kinds citable, shareable and discoverable for the long term.