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What is a naming authority? What is an authority path?
What is a persistent identifier?
What is name resolution?
Why use persistent identifiers?
What resources should be named?

The Name Resolution Service (NRS), developed and maintained by Library Technology Services (LTS), is a comprehensive service for creating, maintaining, and resolving persistent identifiers.

What is a naming authority? What is an authority path?
A naming authority is an organizational entity given the ability to create and maintain persistent identifiers. Naming authorities are arranged in a hierarchical tree structure, where the parent/child relationship indicates administrative oversight. The process of creating a new child naming authority is referred to as delegation: a parent authority delegates some portion of its naming responsibilities to a child authority.

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Every naming authority is given a unique name known as an authority path. An authority path for a given authority includes the path of its parent as a dot-separated prefix. Thus, the hierarchy represented above includes naming authorities with the following authority paths:

FHCL

HUL
HUL.Eresource
HUL.OIS

RAD
RAD.ARCH

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If the HUL.OIS authority delegated a new child authority, Guest, its authority path would be:

HUL.OIS.Guest

What is a persistent identifier?
A persistent identifier is a permanent, location-independent identifier for a network-accessible resource. Persistent identifiers are sometimes referred to as names.

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In this case permanent means that once an identifier is associated with a particular resource it will never be associated with any other resource. Even if the resource itself is ephemeral and becomes inaccessible at some point in time, its persistent identifier will never be reassigned.

Location-independent means that the identifier itself does not specify the location of the resource. In order to access a resource its persistent identifier has to be resolved into a location-specific identifier such as a URL.

What is name resolution?
Name resolution is the process of mapping a persistent identifier (PID) to a URL that retrieves the named resource; the URL locates the resource identified by the persistent identifier:

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If a resource moves or changes the way it is accessed, the mapping between the resource's persistent identifier and URL is updated; the persistent identifier remains unchanged and valid.

Why use persistent identifiers?
In general, important resources should never be directly identified by a URL because URLs can become invalid if the resource is moved or if the way it is accessed changes. (This is the cause of the "404 File Not Found" browser error message.) By adding a layer of indirection into the access process, persistent identifiers will never become invalid. If a resource moves, only the URL to which the persistent identifier resolves needs to be updated; the identifier itself can remain unchanged. As long as persistent identifiers are properly maintained within NRS, 404 errors should never occur when accessing named resources.

What resources should be named?
Digital objects intended for network delivery and accessed through OIS-supported delivery services, such as the Image Delivery Service (IDS) or Page Delivery Service (PDS), must be given persistent identifiers in NRS. Other objects, such as archival masters intended only for storage, can be given persistent identifiers if they meet the following criteria:

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