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reducing the amount of programming required for data access, the costs to develop and maintain the data access portions of an application are also reduced.

Databases and the Web

As technology continues to evolve , so do the database applications that rely on it. Much of this technology evolution has allowed databases to be used for more and varied purposes, and by more users. Consider the beginnings of database technology where access to the information within a database was controlled through custom-developed programs that were written for a specific purpose. Today, the information contained in relational databases is available to a much wider audience due in part to the World Wide Web. Not only is access to the database made easier, Web technology makes it quite easy for users to quickly link to and retrieve related information such as documents or data from other data sources. Where once this type of information access required a substantial development effort, Web technologies have reduced the complexity of building and deploying application architectures that utilize multiple data sources.

With the advent of the Internet and the Web, the architectures of traditional database applications have changed significantly. As Web technologies continue to mature, the relational database has established itself as an integral part of Web-based applications and Web-based database applications are becoming commonplace in corporate computing environments. Corporate intranets, which basically function as an Internet on a corporate LAN/WAN, are quickly gaining popularity with Information Technology (IT) organizations as an efficient way to facilitate communication, streamline business processes, and provide access to information that resides in corporate databases. Although many new applications are designed specifically for intranet architectures, intranets are also being used to provide access to existing database applications and extend the longevity of many legacy systems.

A database is used with an Internet or intranet Web site in a number of ways. To understand how this integration works, consider the different types of pages that can be contained in a Web site. Pages generally follow one of three models:

• Static pages typically deliver static Hypertext Markup Language (HTML) content to the user. These pages can also provide the facility to download files to the user .
• Dynamic pages provide the ability to deliver dynamic content to the user based on the user's input. These pages are often generated using information from a database. These pages usually access the database in a query, or read-only mode. An example of this type of page is one that delivers a stock quote based on a ticker symbol entered by the user.
• Active pages provide the capability to support processing logic and manage database transactions. These pages often use a combination of client-side and server-side processing to support application logic. Because the Web is essentially a stateless environment, this model requires a sophisticated infrastructure that is capable of maintaining application state information, and is aware and responsive to events that occur as a result of application processing.

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The database plays a significant role in both the dynamic and active page types. Most database-enabled Web applications are read-only in nature, in that they simply publish data from the database. These applications provide excellent data browsing capability and intuitive navigation for drilling down or linking to related data. More over, the interface provided by the Web page can easily publish information from multiple databases.

Although most current Web applications simply publish information, database connectivity technologysuch as that offered by Oracle's Web Application Server 3.0is becoming capable of true, secure transaction processing, thereby supporting mission-critical applications. This capability is extremely significant in that it changes the paradigm of the database application architecture. Although the fundamentals of the relational database remain the same, the way in which applications are built, deployed, and managed changes drastically.

As Internet technologies continue to mature, so does the role of the database. Once the database was used for storage and retrieval of simple record-based data, but today it is used for storage and retrieval of complex data types, including text and multimedia data, as well as for storage of business rules and application logic in the form of database scripting languages.

Summary

This chapter described two aspects of a relational database management system: the relational database model and the database management system. The relational model defines relations, which are the underlying database structures; constraints, which are the rules that govern their relationships to one another; and the relational algebra operations that you can perform on relations. Relational database management systems work on sets of data and employ many of the concepts of basic set theory.

A full-featured management system for a relational database is a sophisticated, complex piece of software that functions very much like an operating system. One of the reasons that Oracle has been so successful and widely used is that it has been able to implement the same "logical" database operating system on a variety of host-operating systems. User access to objects in the database is controlled by the RDBMS kernel and the meta-data stored in the data dictionary. Applications never access the data in the actual operating system data files directly; instead, all access is provided through the RDBMS.

Access to RDBMS data is accomplished through nonprocedural requests using SQL. Compared to conventional file system access, SQL provides set-at-a-time as opposed to row-by-row processing. The language elements and usage of SQL are covered in Chapter 4, "Overview of the Oracle Architecture."

The database is rapidly becoming an integral part of Web applications, especially those that reside on corporate intranets. Intranet-based database applications are an extremely efficient way to publish and leverage information from corporate databases. As Web-to-database connectivity technologies mature, the Web will support more transaction processing and mission-critical applications.

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