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PIDA - Persistent Identifiers for Digital Assets

We provide long-lasting references for digital assets accessible to humans and machine agents

Persistent Identifier (PID)

First, an identifier is a string (i.e., a sequence of characters) associated with an information resource that allows identifying that resource within a system. Second,  persistent refers to the need for an identifier to provide access to the object it refers to for years to come. A Persistent identifier (PID) is a long-lasting reference to any digital object on the Web, such as an article, contributor, or organization. In other words, it remains constant as a means of identifying digital objects regardless of changes to their location on the Web. More details can be found here.

Principles of operation

PIDs provided by PIDA are functionally URLs/IRIs. Instead of pointing directly to the location of an Internet resource, a PID points to an intermediate resolution service. The resolution service associates the PID with the actual URL/IRI and returns that location on the web to the client. The client can then complete the transaction in the normal fashion.


Link rot is a very common phenomenon - each and everyone of us has experience the “404-error”  on the web before: Sometimes URLs do not work correctly because Internet resources move, change names or method of access. Once a URL fails, all instances that link to that URL (for example, links in a Web document or a bibliographic record) become invalid and can’t be used any more. By using an intermediate resolver - like PIDA - this can be prevented. Here you can associate your resource with an PID/IRI issued by PIDA. Broken links, i.e. when your resource moves, can then be repaired quickly and with little effort: For this the actual/new URL of the resource needs to be registered/updated at PIDA. We ensure the persistent referencing to your digital resource on the Web.
We commit to running and maintaining this service for the upcoming 10+ years.


The PURL concept was developed by Stuart Weibel and Erik Jul at OCLC in 1995.[2] A PURL service was implemented using Apache HTTP Server. OCLC released versions 1 and 2 of the Apache-based source tree, initially in 1999 under the OCLC Research Public License 1.0 License and later under the OCLC Research Public License 2.0 License.


PIDs look just like URLs because they are URLs (see the example below). A PID has three parts:

  • Protocol - The protocol used to access the PURL resolver, e.g., https. Note: This protocol may differ from that used to access the resource associated with the PID.
  • Resolver address - The IP address or domain name of the PURL resolver, e.g. purls.helmholtz-metadaten.de. This portion of the PID is resolved by the Domain Name Server (DNS).
  • Name - User-assigned name. Note: This name may differ from the name of the resource in the associated URL, e.g., user-assigned-name.

  • Your PID will look like:
    sample PIDA PID