Support National Bibliography Number as external id (NBN URN)

[NeoTheThird]

Many libraries in Europe assign an NBN URN to archived documents that do not have an ISBN. It might make sense to include this as an external identifier.

Example: https://nbn-resolving.org/urn:nbn:de:bvb:19-epub-91046-3

[bnewbold]

This is doable, though I would be curious how many works exist with an NBN which do not have another identifier (DOI, Ark, Handle, OAI-PMH, Wikidata QID, etc) before adding as a release ext_id. Resolving inconsistencies between identifiers can be laborious (eg, if we think NBN "abc" and DOI "efg" are the same work, but wikidata thinks NBN "abc" has DOI "123", that is hard to resolve; easier if we have fewer but better maintained identifiers). I would guess most theses don't get DOIs, but they might have other identifiers.

Here is the wikidata property page, which has some more context and examples: https://www.wikidata.org/wiki/Property_talk:P4109

The resolver URL you gave above did resolve for me, though the example from the wikidata property page does not: https://nbn-resolving.org/urn:nbn:se-2006-13

Having a resolver is great because we can crawl through!

[NeoTheThird]

apparently https://nbn-resolving.org only does germany and switzerland.

Here's sweden: http://urn.kb.se/ (resolves your example, tho not sure they allow url assembly or just the form)
And here's italy, for future reference: http://nbn.depositolegale.it/

edit: here's the url resolvers from the wikidata prop you linked:

https://nbn-resolving.org/$1
http://resolver.obvsg.at/$1 for urn:nbn:at:.+
http://urn.kb.se/resolve?urn=$1 for urn:nbn:se:.+
http://nbn.depositolegale.it/$1 for urn:nbn:it:.+
http://urn.fi/$1 for URN:NBN:FI.+
http://urn.nb.no/$1 for URN:NBN:no.*
https://www.persistent-identifier.nl/$1 for urn:nbn:nl:.+