THE DATABASE APPROACH - Database Design and Development: An Essential Guide for IT Professionals - page 13

Payment
Trans. File

SORT
PAYMENTS

Sorted
Payments

Customer
Master
File

APPLY
PAYMENTS

Sale
Trans. File

Updated
Customer
File

SORT
SALES

Sorted
Sales

Book
Master
File

APPLY
SALES/PRINT
STMNTS

Updated
Customer
File

Billing
Statements

Figure 1-5 Flowchart for billing application.

accounts. If a bank customer has a checking account, a savings account, and a loan
account, data about that customer such as name and address are kept separately in
each of these applications. There is unnecessary and uncontrolled duplication of the
same data in the bank's computer files. Similarly, the possibility of data duplication
exists in the inpatient and outpatient accounts of a medical center. In an auction
business, data duplication is possible in sellers' and buyers' accounts.
Obviously, data duplication results in wasted storage space. In the bank example,
it is very likely that many customers have both checking and savings accounts. In
auction businesses, dealers of art and other such items are customers recorded in
both sellers' and buyers' account applications. In these cases, the wastage of storage
space can be enormous. Multiple input of same data item also requires extra time
and resources that could be applied for other, useful purposes.

Inconsistent Data Data redundancy or duplication of data in your computer files
can cause serious inconsistency in the data. Suppose a bank customer has both
checking and savings accounts. If that person's name, address, or both are different
in the two accounts, then the data about that customer are inconsistent in the bank's
files. Which set of data is correct? It is possible that the name of that customer in
one system is correct and the address as recorded in the other application is correct.
Inconsistency of data is a direct result of data duplication.
Field sizes and formats of the same data item might be different in the various
applications. In the checking and savings accounts, there could be just one long field
for the address to be recorded in textual format. The loan account, being a later
application, could have separate fields for street address, city, state, and zip code.