Large-scale computer applications require rapid access to large amounts of data. A computerized checkout system in a supermarket must track the entire product line of the market. Airline reservation systems are used at many locations simultaneously to place passengers on numerous flights on different dates. Library computers store millions of entries and access citations from hundreds of publications. Transaction processing systems in banks and brokerage houses keep the accounts that generate international flows of capital. World Wide Web search engines scan thousands of Web pages to produce quantitative responses to queries almost instantly. Thousands of small businesses and organizations use databases to track everything from inventory and personnel to DNA sequences and pottery shards from archaeological digs.
Thus, databases not only represent significant infrastructure for computer applications, but they also process the transactions and exchanges that drive the U.S. economy. A significant and growing segment of the software industry, known as the database industry, generates about $8 billion in annual revenue. U.S. companies—including IBM Corporation, Oracle Corporation, Informix Corporation, Sybase Incorporated, Teradata Corporation (now owned by NCR Corporation), and Microsoft Corporation—dominate the world market. This dominance stems from a serendipitous combination of industrial research, government-funded academic work, and commercial competition.
Much of today's market consists of relational databases based on the model proposed in the late 1960s and early 1970s. This chapter provides