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# PERSISTENT IDENTIFIERS:
COMMERCIAL AND HERITAGE VIEWS

## 6/9 – CASE STUDY 4 – URNs and URIs

Readings and training materials

The URN mentioned in the DOI case study is a type of identifier used by the NSL (National Széchényi Library), a Linked Heritage partner, in addition to ISBN.

- ISBN is itself a registered URN namespace
- ISBN-A works through the centralised DOI resolution service, which is the same as a URN resolver
- But – there is no single unique ISBN URN resolver

As we discussed in the DOI case study, a URN is used to “name” an object of interest:

- In principle, it can be used – as the ISBN frequently is – to link to information about the resource
- In practice, URN resolution services are most often used simply to provide persistence of URL linking – that is, to avoid broken Web links
- Since libraries like NSL are the most prolific users of URN resolvers, there is usually some descriptive information at the URL provided by resolving the URN
- This may not (necessarily) be in any kind of “linked data” form.

## URN as a guarantee of URI persistence

URN resolvers such as the one at NSL essentially provide one item of metadata for each URN: an up-to-date Web location, or URL. This is - in effect - the same sort of resolution service as provided by the very simplest application of a DOI, where one unique ID resolves to one URL. And the resolver requires the same type of management when the location of the object is moved for any reason.

## URN resolution at NSL

The URNs created by NSL are integrated as a persistent ID in the NSL’s online catalogue, making the metadata links independent of changes to their internal file servers.

There are two main types of materials in scope for these identifiers at NSL:

- Ebooks in the Hungarian Digital Library
  - 11,000 ebooks, including audiobooks, digitised and born-digital books are identified by URNs
- Digital images in the Hungarian Digital Image Library
  - 70,000 images are identified by URNs

No materials from outside the NSL are given URNs.

Explore further

DOI® System and Internet Identifier Specifications
Compares URN, URL and DOI as identifiers and explains some of the issues raised in this case study

## Lessons from the case study

- URN resolvers are useful for identifying local resources and making their links permanent
- URN does not offer much advantage over DOI