Data Storage Redundancy COBRA

* Data relationships could not be maintained. Early flat-file systems could not easily recognize and manage the natural relationships between data items. One-to-many and many-to-many data relationships were often ignored, and widespread denormalization of the data occurred.

* "Islands of information" developed within organizations, as different departments developed independent flat-file systems. These departmental "islands" were often written in different programming languages, with different file structures, and it was very difficult for a department to share information with other departments. (See Figure 1.4.)

* Widespread data redundancy developed. Each department within the corporate database often duplicated information, leading to the increased costs of data storage, and the possibility of update anomalies when an item was changed within one department but not another.

* Maintenance nightmares ensued. Because these systems had no repository of metadata, program changes became very cumbersome. Whenever a file changed in structure, the programs which referred to the file could not readily be identified, and every program which referenced that file had to be modified and recompiled.

* Tightly-coupled data and programs led to maintenance problems. Because many application programs defined and maintained their own data structures, there was a problem as all new programs were forced to adhere to the calling procedures of the existing programs. The same communications problems exist within object-oriented systems. The Common Object Request Broker (CORBA) standard for object-oriented systems was designed to insure that this problem will not resurface in the future.

* No concurrency control or recovery mechanisms. Systems had no method for simultaneously updating information and no way to roll-forward information in case of disk failure.

* No method for establishing relationships between data items. The relationships between data items are generally lost or introduced with cumbersome data structures, such as repeating fields within records.

Figure 1.4 Islands of information.

This is an excerpt from "High Performance Data Warehousing", copyright 1997.

If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts.  You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.