Database Application System Components

A database application is a business computer system. As such, it has five system components: hardware, programs, data, procedures, and people. We will consider each of these in turn.

Hardware

Computer hardware is required to run the DBMS, application, and other programs. Database applications do not generally require any specialized hardware, but they often require more hardware than file processing systems do. Database systems can be installed on computers of all sizes, from microcomputers to very large mainframes. Depending on its capabilities, a DBMS can occupy from 256,000 to 1 million bytes or more of main memory. Additionally, the DBMS requires CPU time to execute its large number of instructions. If you compare a file processing application to a comparable database application, you will most likely find the database application takes from 15 to 50 percent more CPU time. Thus, faster computer hardware may be necessary for a database system.

Furthermore, because the database system's overhead data can double or even triple the data storage requirements, more peripheral storage, such as disks, may be required than for a comparable file processing application (ignoring storage space savings due to reduced data duplication). Several companies have developed special purpose computers called database machines. These computers, which are dedicated to the task of processing the database, are designed to provide exceptionally fast performance when processing very large databases.

Programs

A variety of programs is needed to support database applications. At the very least, an application requires a database management system and an operating system. In addition, all but the simplest applications require one or more application programs. Further, if the database is shared concurrently, a communications control program is needed. On mainframes, however, the CCP is a separate program. The CCP, the DBMS, and the operating system are supplied by vendors. Usually the operating system is supplied by the hardware vendor, and in many cases, the DBMS and the CCP are provided as well. It is also common, however, for the DBMS and the CCP to be obtained from independent software vendors. Application programs fall into two major types. The first category includes applications that are written in a standard programming language such as COBOL or Pascal. These programs access the DBMS through subroutine calls. A second type of application program consists of programs that are written in the DBMS product's own language. Most such languages came into existence through the back door. That is, the initial version of the DBMS included an interactive query/update language that users began to employ. As users became more proficient in this language, they began to do more complex tasks requiring longer sequences of instructions. DBMS vendors provided methods for storing sequences of query/update commands, and soon these stored commands took on the complexity and capability of application programs. The use of such DBMS-unique languages is particularly common on microcomputers.

Data

As you would expect, the data component of a database application is the database itself. Database contains source data, meta-data in the data dictionary, and overhead data. Source data is the facts stored in the database, such as account numbers, names, and dates. The data dictionary describes the structure of the database. Overhead data is used for lists, indexes, and other data structures that represent record relationships. In most cases, different applications process different, but overlapping, subsets of the database. Some new terminology will facilitate the discussion of database data. The structure of the entire database is called the schema, or the conceptual view. That portion of the database structure that is processed by a particular application is called a subschema, or application view. A subschema is also known as a logical view. For example, the COMPUTER and PERIPHERAL- EQUIPMENT data types together comprise the INVENTORY subschema, or the INVENTORY application view. Application programs are aware only of data that is in their view. This fact has both advantages and disadvantages. The advantage is that data can be protected from unauthorized access. The user of the INVENTORY subschema, for example, is unable to access SOFTWARE data.

Procedures

The fourth system component of a database application is procedures. Both users and the operations staff need documented procedures describing how to run the system. Users need to know how to sign on to the system, how to enter data and commands, how to operate the computer or terminal, and how to employ the system to perform the tasks they need to accomplish.

People

People are the final systems component of a database application. The final category of people involved in database applications consists of the database administration (DBA) personnel. A database may be a shared resource. As such, its design and use must be managed with a view toward all users (sometimes called the user community). The functions of the DBA staff are to protect the database and to resolve conflicts among users. The DBA should be a representative of the community as a whole, not of any particular user or group of users. In this role, the DBA must arbitrate the processing rights and responsibilities of each user.

Imran Zafar writes articles about computer basics and database management such as introduction to deadlocks and free computer dictionary.