Add Journals Online & Print Link in Journal Holdings

[TobiasNx]

https://services.dnb.de/fize-service/gvr/html-service.htm

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I spotted this service at the overview for the upcoming "Datenbezieher"-Workshop of the DNB:
https://wiki.dnb.de/spaces/ILTIS/pages/125420735/Datenbezieher-Workshops

JOP provides an overview if an institution has phyiscal holdings or online access to a resource.

[TobiasNx]

Link structure: https://services.dnb.de/fize-service/gvr/html-service.htm?sid=admin:info&genre=journal&pid=isil%3D[heldBy]%26zdbid%3D[zdbI]&lang=de

[TobiasNx]

Add fallbacks if no zdb is given but only a issn:
http://lobid.org/resources/search?q=issn%3A*+AND+NOT+_exists_%3AzdbId

[acka47]

Maybe we could just use a separate property? Does the ZDB link to JOP in their RDF data? If yes, how?