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the checking balance in the checking accounts application. The same field name
balance
may also represent the savings balance in the savings accounts application.
In this case, the term
balance
is a homonym. In file-oriented data systems, it is hard
to control homonyms.
Synonyms.
If different field names in different applications represent the same
object, these names are known as synonyms. As an example, consider how a student
may be referred to in a college data system. In the student registration system, the
student may be referred to by the field name
student-number
. On the other hand,
in the majors and graduation system, the student may be referred to by the field
name
candidate-number
. The terms
student-number
and
candidate-number
are
synonyms. In file-oriented data systems, controlling synonyms is difficult.
Excessive Program Maintenance
How is program maintenance a problem in
file-oriented systems? Consider the coding of computer programs in file-oriented
applications. These programs are usually written in third-generation languages like
COBOL. A program in languages like COBOL contains two distinct sections. One
section of the program, namely, FD or file definition section, has the structures of
the files used in the program embedded within the program itself. The other section
has the processing logic. Data structures and processing logic are interconnected
and combined together in the program. This means that reference to data is not
independent of the processing logic. There is no data independence.
What is the effect of the lack of data independence in file-oriented systems? Con-
sider all the computer programs that use the customer file for processing. In each
of these programs, the structure of the customer file is embedded within the program
itself. What happens when a new field such as cellular phone number is added to
the customer record? Every one of the programs using the customer file need to be
changed and recompiled, irrespective of whether the program uses the cellular
phone number field or not. Lack of data independence results in excessive program
maintenance.
Productivity Losses
Two main factors cause reduction in productivity while
using file-oriented systems:
•
The same data need to be maintained in multiple places.
•
Because of lack of data independence, multiple programs need to be changed
frequently.
Database Systems Meet the Challenges
As the demand for information escalated, it became urgent to overcome the limi-
tations of file-oriented data systems. With these limitations, companies could not
meet the requirements of increased demand for information. They needed a dif-
ferent approach to storing, retrieving, and managing data. They could not afford
the productivity losses. They could not waste space because of data duplication in
file-oriented systems.
Specialists at Rockwell and General Electric began to work on better methods
for managing data. These methods attempted to overcome the limitations of
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