The length of the number can reach 128 characters. Publishers can assign the DOI to any level of work or product. Attaching a DOI to the whole does not preclude also assigning DOIs to the parts. For example, a book can carry a number, as can a chapter, illustration or table.

The Directory

The directory works, in effect, as a router. Holding all the DOI numbers and the address of the server maintained by the publisher, it serves as an intermediary between the user and the rights-holder. When a publisher moves, changes servers, or sells rights, the new location is updated in the directory, but the number remains the same, always attached to the same content.

This sounds similar to the Persistent URL (PURL) system developed by OCLC. The directory is based on a similar system, Handles©, developed by the Corporation for National Research Initiatives (CNRI). Both systems perform single point resolutions that is, they return a single URL for each item, but the Handle system offers the potential for multiple point resolution, much like an authority record, so that an automated system can deliver different outcomes to a resolution request dependent upon user specified requirements.

The Database

Metadata is essential to commerce as it must be possible to process transactions via unique identifiers without recourse to physical inspection of the items being traded — which may be inconvenient or impossible. Publishers/rights holders would maintain a database that contains the actual content, plus information about the content. Applications of the DOI will require an interoperable scheme of metadata with each DOI; the basis of the DOI metadata scheme is a minimal “kernel” of elements.

The system debuted to mixed reviews at the Frankfurt Book Fair in 1997. At that time, the American Library Association expressed concerns over ways in which copyright law lagged behind the technology involved. The technology for implementing the full DOI system was also lacking. Special browser plug-ins were required to use the Handle© system and publishers were concerned about the lack of connection between the DOI and existing ISBN, ISSN and ISWC numbering systems. Ann Leer, strategic planning advisor for Oxford Interactive Learning at OUP, described the system as “a Dis-Organized Idea, albeit a good one.”

In the last two years, there has been much formalization of the DOI initiative. An international foundation has been formed to provide support for further work. The Foundation exists to support the needs of the intellectual property community in the digital environment, and specifically to promote and develop the use of the Digital Object Identifier. The Foundation developed a set of principles, available from their Web site, governing the use of metadata in the DOI system. It also participates, alongside the Dublin Core and IFLA, in the Interoperability of Data in E Commerce Systems (INDECS) project.

What does this mean for us? The ability to track locations of data on the Web and to have sets of metadata and copyright information available are of great value to catalogers, but the DOI is also broadly defined as a tool for electronic commerce. As information becomes a commodity traded and sold via the Internet, publishers will develop systems such as the DOI for supporting these transactions as well as maintaining a record of copyright. Our methods of acquiring and providing access to it will need to keep pace and evolve as well.