The deep Web has gotten a lot of press these days. The Web is becoming a complex entity that contains information from a variety of source types. It is much more than fixed Web pages. Databases contain information stored in tables created by such programs as Access, Oracle, SQL Server and DB2.
Information stored in databases is accesible only by query.
This is distinct from static, fixed Web pages, which are documents that can be accessed directly. A significant amount of valuable information on the Web is generated from databases. In fact, it has been estimated that content on the deep Web may be 500 times larger than the fixed Web. People sometimes referred to them as specialty databases, subject-specific databases, virtual libraries, and other similar terms. As Web technology develops and greater amounts of information are mounted on the Web, these databases take on primary importance as information finding tools.