Why use a database?

When computer systems were first developed, the data was stored on individual files that were unique to an application or even a small part of an individual application. But a properly designed and implemented DBMS provides many advantages over a flat file PDS system:

• It reduces the application programming effort.
• It manages more efficiently the creation and modification of, and access to, data than a non-DBMS system. As you know, if new data elements need to be added to a file, then all applications that use that file must be rewritten, even those that do not use the new data element. This need not happen when using a DBMS. Although many programmers have resorted to "tricks" to minimize this application programming rewrite task, it still requires effort.
• It provides a greater level of data security and confidentiality than a flat file system. Specifically, when accessing a logical record in a flat file, the application can see all data elements--including any confidential or privileged data. To minimize this, many customers have resorted to putting sensitive data into a separately managed file, and linking the two as necessary. This may cause data consistency issues.

With a DBMS, the sensitive data can be isolated in a separate segment (in IMS/DB) or View (in DB2) that prevents unauthorized applications from seeing it. But these data elements are an integral part of the logical record!

However, the same details might be stored in several different places; for example, the details of a customer might be in both the ordering and invoicing application. This causes a number of problems:

• Because the details are stored and processed independently, details that are supposed to be the same (for example, a customer's name and address), might be inconsistent in the various applications.
• When common data has to be changed, it must be changed in several places, causing a high workload. If any copies of the data are missed, it results in the problems detailed in the previous point.
• There is no central point of control for the data to ensure that it is secure, both from loss and from unauthorized access.
• The duplication of the data wastes space on storage media.

The use of a database management system such as IMS/DB or DB2 to implement the database also provides additional advantages. The DBMS:

• Allows multiple tasks to access and update the data simultaneously, while preserving database integrity. This is particularly important where large numbers of users are accessing the data through an online application.
• Provides facilities for the application to update multiple database records and ensures that the application data in the various records remains consistent even if an application failure occurs.
• Is able to put confidential or sensitive data in a separate segment (in IMS) or table (in DB2). In contrast, in a PDS or VSAM flat file, the application program gets access to every data element in the logical record. Some of these elements might contain data that should be restricted.
• Provides utilities that control and implement backup and recovery of the data, preventing loss of vital business data.
• Provides utilities to monitor and tune access to the data.
• Is able to change the structure of the logical record (by adding or moving data fields). Such changes usually require that every application that accesses the VSAM or PDS file must be reassembled or recompiled, even if it does not need the added or changed fields. A properly designed data base insulates the application programmer from such changes.

Keep in mind, however, that the use of a database and database management system will not, in itself, produce the advantages detailed here. It also requires the proper design and administration of the databases, and development of the applications.