Database systems are designed to manage large bodies of information. Man- agement of data involves both defining structures for storage of information and providing mechanisms for the manipulation of information. In addition, the database system must ensure the safety of the information stored, despite system crashes or attempts at unauthorized access. If data are to be shared among several users, the system must avoid possible anomalous results.
Because information is so important in most organizations, computer scien- tists have developed a large body of concepts and techniques for managing data. These concepts and techniques form the focus of this book. This chapter briefly introduces the principles of database systems.
1.1 Database-System Applications
Databases are widely used. Here are some representative applications:
• EnterpriseInformation
◦ Sales: For customer, product, and purchase information.
◦ Accounting: For payments, receipts, account balances, assets and other accounting information.
◦ Human resources: For information about employees, salaries, payroll taxes, and benefits, and for generation of paychecks.
Databases are widely used. Here are some representative applications:
• EnterpriseInformation
◦ Sales: For customer, product, and purchase information.
◦ Accounting: For payments, receipts, account balances, assets and other accounting information.
◦ Human resources: For information about employees, salaries, payroll taxes, and benefits, and for generation of paychecks.
◦ Online retailers: For sales data noted above plus online order tracking,
generation of recommendation lists, and maintenance of online product
evaluations.
- As the list illustrates, databases form an essential part of every enterprise today,
storing not only types of information that are common to most enterprises, but
also information that is specific to the category of the enterprise.
Over the course of the last four decades of the twentieth century, use of databases grew in all enterprises. In the early days, very few people interacted di- rectly with database systems, although without realizing it, they interacted with databases indirectly—through printed reports such as credit card statements, or through agents such as bank tellers and airline reservation agents. Then auto- mated teller machines came along and let users interact directly with databases. Phone interfaces to computers (interactive voice-response systems) also allowed users to deal directly with databases—a caller could dial a number, and press phone keys to enter information or to select alternative options, to find flight arrival/departure times, for example, or to register for courses in a university.
The Internet revolution of the late 1990s sharply increased direct user access to databases. Organizations converted many of their phone interfaces to databases into Web interfaces, and made a variety of services and information available online. For instance, when you access an online bookstore and browse a book or music collection, you are accessing data stored in a database. When you enter an order online, your order is stored in a database. When you access a bank Web site and retrieve your bank balance and transaction information, the information is retrieved from the bank’s database system. When you access a Web site, information about you may be retrieved from a database to select which advertisements you should see. Furthermore, data about your Web accesses may be stored in a database.
Thus, although user interfaces hide details of access to a database, and most people are not even aware they are dealing with a database, accessing databases forms an essential part of almost everyone’s life today.
The importance of database systems can be judged in another way—today, database system vendors like Oracle are among the largest software companies in the world, and database systems form an important part of the product line of Microsoft and IBM.
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