Online databases may be bibliographic, full-text or non-bibliographic databases. Important aspects of their features and historical development are described by Bourne & Hahn (2003) and shorter by Hahn (1998).
Single databases are made available by database hosts. One of the most influential hosts on the market has been Dialog Information Services, founded in 1971.
Bourne, C. P. & Hahn, T. B. (2003). A History of Online Information Services 1963-1976. Cambridge, Mass.: MIT Press.
Hahn, T. B. (1998). Text Retrieval Online: Historical Perspective on Web Search Engines. Bulletin of the American Society for Information Science, 24(4), http://www.asis.org/Bulletin/Apr-98/hahn.html
On-line databases (core concepts in LIS)