A persistent identifier (PI or PID) is a long-lasting reference to a document, file, web page, or other digital object. Most PIDs have a unique identifier which is linked to the current address of the metadata or content. Unlike URLs, PIDs are often provided by services that allow you to update the location of the object so that the identifier points to the right place without breaking.
Persistent Identifiers covered in this guide:
Permalinks are URLs that are intended to remain the same, limiting the amount of URL changes that can render objects unfindable. These links are often short and easy for people to type. These URLs need to be actively maintained to continue to be persistent.