OpenURL: NISO Standard Syntax for Metadata in URLs

OpenURL is described as both a syntax and a system. The syntax carries metadata and identifiers about one or multiple referents inside a URL, but the OpenURL System itself is not defined: anything that uses the OpenURL transferred data could be said to provide an OpenURL System. In practice the transferred data is used alongside information about the context of a user interested in a particular referent. That user-contextual information is not part of the OpenURL syntax and is instead supplied by other means when the URL is activated.

• NISO standard syntax
• Carries metadata and identifiers about one or more referents
• Provides a syntax for encoding metadata, not a source of metadata
• Restricted to the world of URLs
• User context passed via HTTP headers, digital certificates, cookies or other identification processes

An OpenURL consists of a base URL followed by a query for one or more objects. The factsheet gives the example http://resolver.local.org/getlocal?author=Shelley, in which the base URL addresses a resolver and the query conveys metadata about the referent. This interface can be used to tie together otherwise disparate services, such as centralised resolution systems and local knowledge of available referents.

• Base URL plus a query for one or more objects
• Query conveys metadata about the referent
• Used to link centralised resolution with local knowledge of referents

The DOI system is a system for resolution of identifiers to global services, while OpenURL is syntax allowing the contextualisation of requests to those services to local requirements. The two can be used together to provide a user experience that incorporates both global and local requirements. The factsheet notes a synergy: OpenURL needs a source of identifiers and authoritative metadata, and the DOI system provides a single point in the network for the creation and subsequent redirection of OpenURLs, which is more manageable than asking every content provider to enable the facility.

• DOI system resolves identifiers to global services
• OpenURL contextualises requests to local requirements
• DOI system supplies identifiers and authoritative metadata
• Single network point for creating and redirecting OpenURLs

A key issue in the OpenURL world is transforming a generic link — for example to a publisher's online copy of a journal — into an OpenURL pointing to the right server for a given user, carrying the identifier and metadata needed to create contextually appropriate extended service links. In current deployment this is done only by the referent pointed at by the URL the user first encounters, so the publisher must agree to redirect the HTTP request to the user's local OpenURL-aware server, add the information that server needs, and know that server's location. The centralised resolution service maintained by content producers for DOI names has no way to resolve a DOI name to a locally held copy of the identified entity. The factsheet describes solving the appropriate copy problem as a significant accomplishment in itself, with further opportunities for collaboration beyond it.

• Publisher must redirect the request to the user's local server
• Publisher must add information the local server requires
• Publisher must know the local server's location

OpenURL's use with DOI names sits within the DOI Foundation's wider treatment of identifier interoperability — the ability of independent systems to exchange meaningful information and initiate actions from each other. The Foundation's interoperability factsheet distinguishes syntactic interoperability (recognising a syntax string as an identifier and initiating actions, even where more than one syntax occurs), semantic interoperability and community interoperability. It notes that resources in digital networks may carry identifiers from different public schemes, official standards, de facto schemes or private cataloguing numbering, and that a resource may belong to more than one domain.

• Syntactic interoperability
• Semantic interoperability
• Community interoperability

OpenURL is documented in the "DOI System and OpenURL" factsheet, one of a series of technical factsheets published on the DOI Foundation's Resources pages. Related factsheets in the same series cover subjects including Key Facts on the Digital Object Identifier System, Designing DOI Applications, Identifier Interoperability, the indecs Framework, DOI System and Cloudflare, DOI System and Standard Identifier Schemes, DOI System and the Handle System, DOI Resolution Documentation, DOI System and the ISBN System, and DOI System and Persistent URLs (PURLs). The Resources pages also hold FAQs about the DOI system, a news archive and the "doi" URI scheme document. Material on the site is shareable under a CC-4.0 attribution licence.

• Factsheet: DOI System and OpenURL
• Companion factsheet: DOI System and Persistent URLs (PURLs)
• Companion factsheet: Identifier Interoperability
• FAQs, news archive and DOI URI Scheme document
• Site content shareable under a CC-4.0 attribution licence