Examples
Worked examples
- Is an instance
A researcher clicks a citation in a PubMed or Scopus search result. The database constructs an OpenURL request encoding the article's metadata (journal title, ISSN, volume, issue, page, or DOI) and sends it to the researcher's institution-specific link-resolver base URL. The resolver checks that metadata against the library's knowledge base, finds that the library has current online access to that journal through a particular platform, and presents (or auto-redirects to) the specific full-text link on that platform -- rather than sending the researcher to a paywall.
- Is an instance
A library implements Ex Libris's Alma Link Resolver (or a comparable product such as SFX, EBSCO LinkSource, ProQuest 360 Link, or the OCLC WorldCat knowledge base) and loads its journal and e-book holdings into the associated knowledge base using KBART-conformant title lists supplied by its content providers. When a title's coverage dates or embargo change, the library updates the knowledge base -- typically via a refreshed KBART file -- so the resolver's answers about full-text availability stay accurate.
Counter-examples
Looks similar, but isn't
- Not an instance
A DOI resolver (doi.org) is not a link resolver in this sense: it takes a single persistent identifier and redirects every user, regardless of institution or subscription status, to the one canonical location the DOI registrant has designated for that object. A link resolver instead takes citation metadata (which may or may not include a DOI) and returns a different, institution-specific answer depending on what that particular library currently subscribes to -- the same citation can resolve to full text for one library's patrons and to a paywall notice for another's.
Editorial commentary
A link resolver is OpenURL-based library-discovery software that takes a citation encountered anywhere in a researcher’s workflow — a database search, a discovery-layer result, a reference manager, Google Scholar — and resolves it to the specific full-text access a given institution’s library actually provides. It is the software behind the “Find It”, “Get It”, or “Get Full Text” button libraries embed across the platforms their patrons search.
How the resolution process works
The process rests on the OpenURL standard, formally ANSI/NISO Z39.88-2004 (R2010), The OpenURL Framework for Context-Sensitive Services. When a researcher clicks a citation in an OpenURL-compliant source (a database, discovery layer, or citation manager), that source constructs a structured link — a ContextObject, in the standard’s terminology — encoding the citation’s identifying metadata (journal title, ISSN or ISBN, volume, issue, page range, and/or a DOI) along with contextual information about the requester. That link is sent to the institution’s link-resolver base URL rather than directly to a publisher. The resolver parses the metadata, checks it against the library’s knowledge base — the underlying inventory of which packages, platforms, and coverage date ranges that library currently has access to — and, if a match exists, constructs and returns (or redirects the user to) the specific full-text link on the platform where that library’s access lives. If no match exists, the resolver typically offers alternatives instead: interlibrary loan, a document-delivery request, or a search of the library catalog.
Why the knowledge base has to stay accurate
A link resolver is only as reliable as the knowledge base behind it. Because a single citation can be licensed through several different platforms, aggregators, or a publisher’s own site simultaneously — each with different coverage dates and possible embargoes — the knowledge base has to be kept current on exactly which titles, and which date ranges within those titles, a library’s subscriptions cover. That holdings data comes from content providers and is standardized using KBART (NISO RP-9-2014), the Recommended Practice that defines a common tab-delimited format for title-level holdings so any provider can supply data any knowledge-base vendor can ingest without a bespoke mapping exercise. KBART does not replace OpenURL or link-resolver software — it feeds the knowledge base that link resolvers query, and stale or malformed KBART files are the most common cause of a resolver returning a broken or misleading “no full text available” result for a title the library actually subscribes to.
Named implementations
Link-resolver software is typically bundled with, or sold alongside, a library’s electronic-resource-management or discovery system. Established products include Ex Libris’s SFX link resolver and the Alma Link Resolver (part of the Alma platform), EBSCO’s LinkSource (paired with the EBSCO Integrated Knowledge Base), ProQuest’s 360 Link, and the OCLC WorldCat knowledge base, which drives OpenURL resolution across OCLC’s WorldCat-based discovery services. Most academic and research libraries operate one of these (or a comparable product) rather than building resolver software independently.
Worked examples
- A researcher clicks a citation in a PubMed or Scopus search result. The database constructs an OpenURL request encoding the article’s metadata and sends it to the researcher’s institution-specific link-resolver base URL. The resolver checks that metadata against the library’s knowledge base, confirms current online access to that journal, and presents the specific full-text link on the correct platform.
- A library loads its holdings into its link resolver’s knowledge base using KBART-conformant title lists from its content providers. When coverage dates or an embargo period change, the library updates the knowledge base — typically via a refreshed KBART file — so the resolver’s full-text answers stay accurate rather than pointing to content no longer (or not yet) available.
Counter-example
A DOI resolver (doi.org) is not a link resolver in this sense. A DOI resolver takes a single persistent identifier and redirects every requester, regardless of institution, to the one canonical location the DOI registrant has designated. A link resolver instead takes citation metadata — which may or may not include a DOI — and returns a different, institution-specific answer depending on that library’s current subscriptions: the same citation can resolve to full text for one library’s patrons and to a paywall or document-delivery option for another’s. See DOI and Persistent Identifier (PID) for the distinct, fixed-target resolution model.
Related terms
See CASRAI’s entries on KBART (the metadata-exchange format that feeds a link resolver’s knowledge base), NISO Recommended Practice (RP), DOI, and Persistent Identifier (PID). For the broader identifier and metadata-infrastructure landscape these systems sit within, see the Persistent Identifiers & Research Information Systems cluster hub and the Scholarly Publishing cluster hub.
Frequently Asked Questions
What does a link resolver actually do?
A link resolver is OpenURL-based software that takes citation metadata encountered in a database, discovery layer, or reference manager and checks it against a library’s knowledge base of current subscriptions, then routes the researcher to the specific full-text copy that library provides. It is the mechanism behind the “Find It”, “Get It”, or “Get Full Text” buttons libraries embed across the platforms their patrons search.
How does a link resolver decide whether I get full text or a paywall?
When a citation link is sent to the library’s resolver base URL, the resolver parses the metadata and compares it against the library’s knowledge base — the record of exactly which packages, platforms, and coverage date ranges that library currently has access to. If a match exists, it returns the specific full-text link; if not, it typically offers alternatives instead, such as interlibrary loan, a document-delivery request, or a search of the library catalog.
How do libraries set up and maintain a link resolver’s knowledge base?
Libraries load their holdings into the resolver’s knowledge base using KBART-conformant title lists supplied by their content providers, then refresh those files whenever coverage dates or embargoes change. Stale or malformed KBART data is the most common cause of a resolver reporting “no full text available” for a title the library actually subscribes to.
Is SFX a link resolver?
Yes — SFX, from Ex Libris, is one of several established link-resolver products, alongside the Alma Link Resolver (also Ex Libris), EBSCO’s LinkSource, ProQuest’s 360 Link, and the OCLC WorldCat knowledge base. Most academic and research libraries run one of these, or a comparable product, rather than building resolver software independently.
What’s the difference between a link resolver and a DOI resolver?
A DOI resolver (doi.org) redirects every requester to the same fixed location that a DOI’s registrant designated, regardless of who is asking. A link resolver instead evaluates citation metadata against a specific library’s current subscriptions, so the same citation can resolve to full text for one institution’s patrons and to a paywall or document-delivery option for another’s.
Machine-readable encodings
Use in your systems
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