Which of the following is NOT a link resolver?

• A. PURL
• B. SFX
• C. OpenURL
• D. DOI

Answer: (A)

Link resolvers in libraries are systems that take citation metadata and search your library’s holdings to provide direct links to available full-text resources. They rely on frameworks like OpenURL to carry the citation information from where you found it to the resolver, which then returns a usable link to access the item across different providers.

SFX is a concrete example of a link resolver, designed exactly to connect a citation to the library’s holdings. OpenURL is the standard protocol those resolvers use to receive the metadata and perform the lookup. DOI represents a persistent identifier that can be resolved to a location, and while it’s used in linking workflows, it isn’t itself a link resolver.

PURL, on the other hand, is a persistent URL service that redirects a stable URL to whatever the current address is. It does not perform the metadata-driven lookup across licenses and holdings that a link resolver does, so it isn’t a link resolver. That’s why it’s the correct choice for NOT being a link resolver.