Databases are not merely a collection of files. Rather, a database is a central source of data meant to be shared by many users for a variety of applications. The heart of a database is the database management system (DBMS), which allows the creation, modification, and updating of the database; the retrieval of data; and the generation of reports and displays. The person who ensures that the database meets its objectives is called the database administrator.
The effectiveness objectives of the database include the following:
- Ensuring that data can be shared among users for a variety of applications.
- Maintaining data that are both accurate and consistent.
- Ensuring that all data required for current and future applications will be readily available.
- Allowing the database to evolve as the needs of the users grow.
- Allowing users to construct their personal view of the data without concern for the way the data are physically stored.
The foregoing list of objectives provides us with a reminder of the advantages and disadvantages of the database approach. First, the sharing of the data means that data need to be stored only once. That in turn helps achieve data integrity, because changes to data are accomplished more easily and reliably if the data appear once rather than in many different files.
When a user needs particular data, a well-designed database anticipates the need for such data (or perhaps it has already been used for another application). Consequently, the data have a higher probability of being available in a database than in a conventional file system. A welldesigned database can also be more flexible than separate files; that is, a database can evolve as the needs of users and applications change.
Finally, the database approach has the advantage of allowing users to have their own view of the data. Users need not be concerned with the actual structure of the database or its physical storage. Many users are extracting parts of the central database from mainframes and downloading them onto PCs or handheld devices. These smaller databases are then used to generate reports or answer queries specific to the end user.
Relational databases for PCs have improved dramatically over the last few years. One major technological change has been the design of database software that takes advantage of the GUI. With the advent of programs such as Microsoft Access, users can drag and drop fields between two or more tables. Developing relational databases with these tools has been made relatively easy.