In December 1993 Edward A. Fox of Virginia Polytechnic Institute and State University (Virginia Tech) issued Sourcebook on Digital Libraries. Version 1.0. Remarkably the text was 410 pages long with a 22-page index.
The earliest references in the bibliography were:
Gerald Salton, Automatic Text Processing: The Transformation, Analysis, and Retrieval of Information by Computer, Addison-Wesley, 1989.
Capitalizing on the Nation’s Knowledge: Making Use of What We Know, A Statement by John Seely Brown before the Subcommittee on Science, Technology, and Space of the Committee on Commerce, Science, and Transportation, United States Senate, 15 September 1989.
Most references in this then-new field were dated 1992.