A Persistent Unique Identifier (PID) is a string of letters and numbers used to distinguish between and locate different objects, people, or concepts. A well-known example of a PID is a Digital Object Identifier (DOI) which is used to locate specific digital objects, frequently a journal article. Another example is ORCiD, a PID for researchers.
PIDs can be created by an institution that maintains a collection of resources. For example, the National Library of Medicine’s Medical Subject Headings (MeSH) assigns a Unique ID to each term. Alternatively, a third party can create and track PIDs across many institutions, each of which can then assign PIDs to resources, objects, or other concepts. For example, DOI’s are maintained by the International DOI Foundation (IDF). The IDF works with various organizations to register new digital objects and to ensure that no two objects receive the same DOI. The organizations that manage registration include DataCite and CrossRef.
Digital Object Identifiers (DOIs) for journal articles
ORCID IDs for researchers
This resource discusses PIDs for data specifically, and highlights one of the main registrant organizations for DOIs for data - DataCite: DataCite: Lessons Learned on Persistent Identifiers on Data: http://ijdc.net/index.php/ijdc/article/view/11.2.39
This discusses the relationships between different PIDs and provides necessary information to understand how PIDs function together in the broad scholarly ecosystem: Persistent Identifiers for Scholarly Assets and the Web: The Need for an Unambiguous Mapping: http://www.ijdc.net/article/view/9.1.331