Libraries have been participating in CrossRef since 2001, and there are currently over 1000 libraries with accounts on the CrossRef system. Libraries can now use CrossRef at no charge, although they are still required to register with CrossRef in order to obtain an account. Please see and related information there for details on joining CrossRef.

Libraries use the CrossRef system in two main ways:

(1) To retrieve digital object identifiers (DOIs) to create reliable links from their local database and catalogue records to publishers' full text, or to enhance localized resolution where the DOI is not already available from the source (i.e., citing) document. Because DOIs greatly streamline linking and data management processes for publishers, more publishers are beginning to require that the DOI be used as the primary linking mechanism to full text. In a process described in detail at, bibliographic metadata is used to query the CrossRef system and the corresponding DOI is then returned.

(2) As a source of metadata to enhance their OpenURL-based local link resolvers; the CrossRef system will accept a DOI as input and return an associated bibliographic citation (the query spec pointed to above also describes metadata and OpenURL queries). Some libraries have created their own link resolvers, and many libraries purchase the services of one of a number of vendors who now provide link resolution software.

Definitions: A link resolver is a system for linking within an institutional context that can interpret incoming OpenURLs, take the local holdings and access privileges of that institution into account, and display links to appropriate resources, allowing the library to provide a range of library-configured links and services. The OpenURL is an HTTP request (GET or POST) that, when clicked by the user, delivers metadata and/or identifiers for the referenced work to a local service component.

How the DOI and OpenURL work together: The DOI and the OpenURL work together in several ways. First, the DOI directory (, where link resolution occurs in the CrossRef system) is OpenURL-enabled. This means that it can recognize a user with access to a local resolver when a cookie is set on the user's machine. When such a user clicks on a DOI, the CrossRef system does two key things: (1) it redirects that DOI back to the user's local resolver, and (2) it allows the DOI to be used as a key to pull metadata out of the CrossRef database, metadata that is needed to create the OpenURL targeting the local link resolver. As a result, the institutional user clicking on a DOI is directed to appropriate resources.

The CookiePusher: In order to take advantage of localized linking, a cookie must be set on the user's machine. For information on the Cookie Pusher script, please see (Note that the reason this CookiePusher information is available at via SFX is historical, due to their role in prototyping this functionality.)

In order for the cookie to be set by the, the BASE-URL of the user's localized linking server must be recognized by BASE-URLs are collected from library affiliates for this authorization. To set a cookie after your BASE-URL has been registered, go to The user must then add the cookie provided by to the cookie file for his/her web browser. This cookie will contain the URL prefix for the local content server (e.g. and the user's web browser is then OpenURL-enabled, which means that will redirect relevant requests to his/her local resolver.

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