Overview

The Name Resolution Service (NRS) is a Harvard Library service for creating, maintaining, and resolving URNs, also called persistent identifiers or Names.  URNs are location-independent names for network-accessible resources. "Name Resolution" is the process of converting a URN into the URL to the resource. If a resource's URL changes, the mapping between the resource’s URN and URL can be updated; the URN itself, however, remains unchanged and valid. By using URNs, curators and researchers can cite a URL that will always point to the same resource. If the resource itself becomes unavailable at some future time, the URN will never point to a different resource.

The NRS has several components:

1. An administrative service that manages the metadata necessary to perform naming services
2. An Admin UI to allow registered users to create and maintain URNs
3. An API that allows registered applications to interact with the administrative service without using the Admin UI
4. An HTTP-based resolution service that performs naming resolution using browser redirection
5. An API that returns information about URNs rather than resolving the URN

 
What is a persistent identifier?
What is name resolution?
Why use persistent identifiers?
What resources should be named?

Who can use NRS?

Any Harvard administrative organization is eligible to use NRS.

How are persistent identifiers created?

The process of creating a persistent identifier is also known as "naming" a digital resource. The majority of persistent identifiers are created for digital objects when they are deposited into the Digital Repository (DRS). Objects already stored in the DRS can be named by using the DRS Web Admin. NRS has its own Admin interface that supports naming of objects inside or outside of DRS.

What is a Naming Authority? What is an Authority Path?

Every URN in NRS has to be unique. In order to give groups at Harvard the most flexibility in creating unique URNs, groups are given control over a set of URNs that begin with a specific set of characters. A Naming Authority is the set of characters an administrative unit uses to create URNs. Groups can create child Naming Authorities in a hierarchical tree structure to further split up a Naming Authority.  URNs display the parent child relationships by using a period between the parts. For instance, URN-3:RAD is a parent Naming Authority, and URN-3:RAD.ARCH is a child Naming Authority.

The root naming authority in NRS (URN-3) is administered by LTS. LTS has established a number of top-level naming authorities under URN-3 that correspond to Harvard schools or administrative units:

FHCL is Harvard College Library; RAD is Radcliffe Institute; and RAD.ARCH is Radcliffe Archives.

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:

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.

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:

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: