American MemoryThe National Digital Library Program: Archived Documentation

The Library of Congress / Ameritech National Digital Library Competition (1996-1999)

Handle Server [May 4, 1998]

Overview   |   More on Handles and Naming Authorities   |   A Global System of Handle Servers

The Handle System is the mechanism developed by the Corporation for National Research Initiatives (CNRI) to support a system of global identifiers for resources on the Internet. A number of such schemes for Uniform Resource Names (URNs) have been proposed through the Internet Engineering Task Force. In December 1995, the active participants in this effort agreed to deploy their proposed systems in a compatible fashion that will allow practical evaluation and continuing development.

The CNRI Handle System incorporates distributed Local Handle Services and a Global Handle Registry that maintains information about the location of all the local servers. A primary task of the Handle System is to provide an address lookup service. Each item in the digital library will be given a handle, an identifier that is globally unique, valid for the long term (persistent), and independent of its current location in a particular file attached to a particular computer. If presented with a handle, the Handle System will supply data that allows a user (or, more likely, a computer program on behalf of a user) to access the item identified by the handle.

Here is a simple example:

The Library's local handle server would have a two-part record for each item, associating a handle with the data necessary to access the item identified by the handle. In this simple example, the record associates the handle with the URL for the digitized image.

Diagram of handle-server record

When a program presents the handle server with the handle, the handle server resolves the handle and supplies the program with the data, in this instance a URL. The program can then use the URL to retrieve the image.

All external references, whether from the Library's MARC records or finding aids or from online research papers or teaching materials developed elsewhere, should use the handle, not the URL, so that when the Library moves this file, the only change that would have to be made is to the record in the handle server. (This digital archive is being built for the long term. The Library will not move files often, but developments in the computing industry over the coming decades are unpredictable and not under the Library's control. It would be short-sighted to adopt a design that did not allow items to be moved or filenames to be changed.)

Handles for NDLP resources will have certain characteristics:

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