Handle Server: Overview

The Handle Server 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.

A primary task of the handle server is to provide an address lookup service. Each item in the digital library is 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 server 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:

• A particular photograph from the Detroit Publishing collection has the control identifier 4a32371. A possible handle for a thumbnail version of this image is hdl:loc.pp.detroit/4a32371t, where "hdl:" indicates that the identifier is a handle within the CNRI scheme and "loc.pp.detroit" identifies the naming authority that assigned this name.
• The image can currently be retrieved by the World Wide Web's HTTP (HyperText Transfer Protocol) using the URL (Uniform Resource Locator): http://lcweb2.loc.gov/image/4a/4a30000/4a32000/4a32300/4a32371t.gif

The handle server has 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.

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:

• Each handle will follow a hierarchical pattern, essential for any naming scheme that guarantees uniqueness without requiring centralized pre-registration of each item.
• The top level of the hierarchical identifier ("loc") will specify the Library of Congress as the naming authority within a global system. Within "loc," authority for naming items will be further delegated, in this example to the Prints and Photographs Division. Within the division, naming authority may be delegated further, to the level of aggregate, a grouping established for digital storage management. In many cases, the aggregate will correspond to an American Memory collection. In other cases, an American Memory collection may comprise several aggregates.

For more details, continue through this section on the Handle Server:

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

Handle Server

(8/11/96)