Database Systems

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Ø  The importance of database design


Database design refers to the activities that focus on the design of the database structure that will be used to store and manage end-user data.

A well-designed database facilitates data management and generates accurate and valuable information. See the limitations on file system data management. Then you will realize the importance of database system data management.

The limitations of file system data management:
·         It requires extensive programming.
·         It cannot perform ad hoc queries.
·         System administration can be complex and difficult.
·         It is difficult to make changes to existing structures.
·         Security features are likely to be inadequate.
Those limitations, in turn, lead to problems of structural and data dependency.
Structural dependence exists when it is impossible to make changes in the file structure without affecting the application program’s ability to access the data.
Example: adding a customer date-of-birth field to the CUSTOMER file
Data dependence exists when it is impossible to make changes in the data storage characteristics without affecting the application program’s ability to access the data
Example: changing a field from integer to decimal, require changes in all the programs that access the file
The practical significance of data dependence is the difference between the logical data format (how the human being views the data) and the physical data format (how the computer must work with the data).
The file system’s structure makes it difficult to combine data from multiple sources and its lack of security renders the file system vulnerable to security breaches. The organizational structure promotes the storage of the same basic data in different locations. (Database professionals use the term islands of information for such scattered data locations.) Because it is unlikely that data stored in different locations will always be updated consistently, the islands of information often contain different versions of the same data. This leads to the data redundancy and data inconsistency.
Data redundancy exists when the same data are stored unnecessarily at different places.

Data inconsistency exists when different and conflicting versions of the same data appear in different places

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