A PID (persistent identifier) is a unique ID number or code string that identifies a resource in a manner that is persistent over time. A PID is used to uniquely identify objects, individuals, and organizations. That way, it is possible to separate resources that could otherwise be mistaken for one another.

There are different types of PID depending on what needs to be identified and on which organization is behind the PID. A common example of a PID that we have all encountered is the ISBN (International Standard Book Number) that identifies a certain edition of a book.

In a digital context, the PID is a unique and permanent reference that makes it possible to find and reuse digital material. PIDs are used to refer to digital objects, such as websites, documents, or other files. As a rule, a PID is similar to a hyperlink, and can be discovered online. But unlike most weblinks, there is an infrastructure behind a PID that makes sure it always directs to the right resource, even if the resource is moved in the future. Apart from the direction to an object, there are usually other metadata connected to a PID, for example persistent descriptions. Because of that, every PID in an online PID system can be discovered and interpreted by both humans and machines. 


DOI (Digital Object Identifier) is a common persistent identifier that has gained popularity in identifying various online resources, among them research data. 

All research data published in the SND research data catalogue are assigned a DOI. The DOI links back to a persistent description of the dataset that does not change regardless of whether the data files are moved. The DOI will always be discoverable through, and if the dataset is de-published, information about it can still be found through the DOI. 

The reason for assigning DOIs to data is, among other things, to ensure that you can uniquely cite a certain version of a data material. The citations mean that you as a researcher get credit when data from your project is reused. These days, many scientific journals require that research data are accessible and have a PID, for example a DOI, in order to publish articles or studies based on those data. 

Example of a DOI
This DOI points to Swedish version of The National SOM Survey 1995, version 1.0. If the SOM Institute decides to create and publish a new version of this same dataset, the new version will receive a new DOI. Even if the previous version of the dataset has already been used in analyses and publications, there is less risk of misunderstanding as it is possible to reference both versions in a consistent manner. If you go to the older version of the dataset, you will be informed that there is a newer version. 


ePIC (Persistent Identifier Consortium for eResearch) is a PID based on the Handle system. The main focus for this PID is to provide identifiers for research data in the early stages of the research process, especially when large amounts of data or data files are generated and it is uncertain which parts of the data material will be cited in the future. Unlike for DOI, there is no need for a persistent description of the data to create an ePIC PID, so we recommend DOI for data that will be published long-term.

Example of an ePIC PID

This specific ePIC is a demonstration PID that points to the Swedish version of this information page. 


As a researcher you have every reason to create, maintain, and use an ORCID (Open Researcher and Contributor ID). ORCID is a PID that permanently identifies you as a creator or author. By doing so, the research data, publications, and other scientific creations you have contributed to can be uniquely linked to you. 

An ORCID can prevent the misidentification that can happen if you have the same name as another researcher, or if you change your name or organization. ORCID also makes it easy to link to a list of publications or a CV. Some publication services will automatically connect new publications to ORCID accounts, which means you don’t have to update all information yourself. Many research funding bodies and journals require that you have an ORCID when you apply for a grant or submit a manuscript. 

Example of an ORCID

This ORCID, 0000-0002-1825-0097, points to a fictitious researcher, Josiah Carberry. In his ORCID post (created for demonstrative purpose), you can see Josiah’s organizational affiliations and some of his publications. There are a couple of variations of Josiah’s name, which can help to ascertain whether he is the correct contributor in a certain context. Additionally, there is a connection to Josiah’s author ID in another system (Scopus Author ID). If Josiah Carberry had been a real researcher, he could, with the help of various metadata services, have kept the ORCID post up to date with new and current information. 


For research organizations, there is the Research Organization Registry, ROR, which provides persistent identifiers that uniquely point to specific research organizations, just as how ORCID points to a specific individual. A ROR ID contains useful metadata for the organization and refers to other identifiers and organizations connected to it. 

A ROR ID can be used to uniquely identify and link to a research organization in, for example, a publication or grant application. In the SND research data catalogue, ROR ID is used to identify the responsible research principals and the funding bodies that fund a research project.

Example of a ROR ID

This ROR ID identifies Swedish National Data Service. It is usually the English name of a research organization that is their primary entry in the ROR directory.