Background

DOI^® names for articles in scholarly and technical journals generally resolve to the publishers' websites. Retrieving the articles from those websites typically requires a fee or a subscription. Libraries commonly purchase copies of journals to keep in their local collections for their users, and they often own or subscribe to multiple copies of journals. For those institutions' users, the address to which a DOI name should appropriately resolve depends on the location or affiliation of the user who is making the resolution request, and the appropriate choice is usually one of the institution's local copies.

The International DOI Foundation, CrossRef, CNRI, libraries and library services providers came to refer to this as the "appropriate copy problem," and began collaborating on a solution and developing a prototype in 1999. (For details see D-Lib Magazine, September 2001, "Linking to the Appropriate Copy".)

The combination of the DOI name resolution system, the CrossRef Metadata Database, and OpenURL provides a practical solution to the appropriate copy problem for libraries. The key components of this architecture are (1) local content servers that can match a query for an item to a library's appropriate copy; (2) a DOI name resolution system that can redirect a query to a local content server; (3) a way for the originator of the query to identify the appropriate local content server to the resolution system; and (4) a source of metadata about the item sufficient for the local content server to match the query to the appropriate copy.

The solution offered by CrossRef to its library affiliate members is as follows: users in a member institution click on a DOI name, and the DOI name and a cookie (previously set in the user's web browser through a "CookiePusher" mechanism) are sent to the DOI^® System proxy server. The proxy server recognizes the local content server identified in the cookie, constructs an OpenURL containing the DOI name, and sends it to the user's local resolver by way of an HTTP "redirect" to the user's browser. The local resolver sends the DOI name in OpenURL format to CrossRef. CrossRef returns metadata for the item named by the DOI name. The local content server recognizes this as a locally-held article, constructs a URL pointing to the item, and sends it to the user's browser as an HTTP "redirect".

If the article is not locally-held, the local content server returns the request to the proxy server, with a flag set to indicate there is no local copy, and the proxy server resolves the DOI name as it ordinarily would, redirecting the user's browser to the publisher's site.

For a complete description of this process and how libraries can participate in this local linking solution, see the documentation on local linking for CrossRef library affiliates on their website.

The current solution is specific to CrossRef which, at the time of this writing, remains the source of most DOI names and associated metadata relevant to the problem. This situation is, however, changing with the continued growth of the DOI System and it is generally acknowledged that multiple sources of metadata will have to be accommodated in the future. This will require adjustments both in the DOI name resolution data and in the behavior of local content servers. The groups that came together to solve the initial "Appropriate Copy Problem" recognize this, have held preliminary discussions on the topic, and anticipate the need for additional collaborative efforts as the situation evolves.

The DOI System Proxy Server and Setting the Cookie

A "CookiePusher" mechanism (see D-Lib article for details) is used to set a cookie in the user's browser that is recognized by the proxy server and contains the URL to which the proxy server will redirect the DOI name resolution request. To prevent unauthorized users from setting cookies and redirecting traffic to their own personal resolvers, a BASE-URL list, containing the URLs of the authorized local content servers, is included in the CookiePusher. The BASE-URL can be the URL for a script or a directory, or even a top level domain, but it must be an OpenURL aware server. If the BASE-URL in the request is not in the list, the script will not set the cookie, but will return a "no cookie for you" message. BASE-URLs are collected from CrossRef affiliates when they join.

The CookiePusher script runs on the DOI System website (http://www.doi.org). The proxy server (http://dx.doi.org) is under the DOI.ORG^® domain. The URL for the CookiePusher script is:

http://www.doi.org/cgi-bin/pushcookie.cgi

A sample request to the CookiePusher containing the URL prefix of the local content server is:

http://www.doi.org/cgi-bin/pushcookie.cgi?BASE-URL=http%3A//university.library.edu%3A9003/local_linking/

URI hexadecimal (%) encoding is recommended.

The request to add the cookie to the user's web browser's cookie file is usually hidden from view on an introductory or login web page, using a transparent GIF.

<img src="http://www.doi.org/cgi-bin/pushcookie.cgi?BASE-URL=
http%3A//university.library.edu%3A9003/local_content_server/">transparent.gif</img>

A sample cookie, with a TTL of 24 hours, is:

Name: Demo-OpenURL
Information: \"http://university.library.edu:9003/local_content_server"
Domain: .doi.org
Path: /
Server Secure: no
Expires: Wednesday, October 23, 2004 10:28:11 PM

After the cookie is set, the proxy server will recognize the local content server identified in the cookie, construct an OpenURL containing the local content server URL and the DOI name:

http://university.library.edu:9003/local_content_server/openurl?doi=10.1000/demo_DOI

and send the request by way of an HTTP "redirect" to the local content server.

If there is no local copy of the content, the local server must return the request to the proxy server with a "nols=y" flag set. The proxy server will then resolve the DOI name and direct the user to the publisher's content. (The deprecated setting "nosfx=y" used in the prototype is still supported.) Correctly setting the "no local service" flag is critical to avoiding infinite loops.

http://dx.doi.org/openurl?id=doi:10.1000/demo_DOI&nols=y