A library must have a collection of materials that carry information. In addition to its collection, a library must have some kind of organizational rules and some kind of finding mechanisms, collectively known as its "technologies" (e.g., catalogs, search engines). Finally, every library serves one or more identifiable communities of users. A library becomes digital as the collection, the technologies, and the relation to the users are converted from printed formats (i.e., books and paper) to electronic formats. First, the collection itself must be made machine readable. Next, the technologies must be converted to computer-based forms. Finally, an interface to members of the user community must be provided in computer formats. A digital library may be as small as the set of files on one person's computer, organized into a hierarchical directory structure and supplemented by the owner's personal scheme for naming files and...