Data redundancy occurs in database systems which have a field that is
repeated in two or more tables. For instance, in case when customer
data is duplicated and attached with each product bought then
redundancy of data is a known source of inconsistency, since customer
might appear with different values for given attribute.
Data integrity refers to the validity of data. Data integrity can be
compromised in a number of ways:
Human errors when data is entered.
Errors that occur when data is transmitted from one computer to another.
Software bugs or viruses.
Hardware malfunctions, such as disk crashes .
Natural disasters, such as fires and floods.
There are many ways to minimize these threats to data integrity. These
Backing up data regularly
Controlling access to data via security mechanisms
Designing user interfaces that prevent the input of invalid data
Using error detection and correction software when transmitting data
Data processing Cycle
INPUT: In this step the initial data, or output data, are prepared in some convenient
form for processing. The form will depend on the processing machine. For example,
when electromechanical devices are used, the input data are punched on cards; but
if electronic computers are used, the input data could be recorded on any of several
types of input medium, such as cards, tapes, disks, and so on.
PROCESSING: In this step the input data are changed, and usually combined
with other information, to produce data in more useful form. Thus, paychecks
may be calculated from the time cards, or summary of sales for the month may
be calculated from the sales orders. The processing step usually involves a
sequence of certain basic processing operations.
OUTPUT: Here the results of the preceding processing steps are collected.
The particular form of the output data depends on the use of data. For
example, output data may be paychecks for employees, a printed summary of
monthly sales for management, or simply data to be stored for further
processing at a later date.
E.g. During the semester an instructor give five unit examinations. At the end of
the semester the grades must be processed and the final grade sheet for the
class submitted to the department. The input data are the students names and
the five scores. This input is usually recorded in the instructor’s record book,
with the names in alphabetical order. The instructor processes the input data
by averaging the five examinations and then determining the equivalent letter
grade of each student. The output data will consist of the students names and
their letter grades, with the names in alphabetical order on the final grade
Expanded Data Processing Cycle
Origination. Origination is a steps which refers to the process of collecting the
original data. An original recording of the data is called a source document.
For example, the source documents for the determination of student grades
are the graded test papers of the students. Note that if there were any
questions concerning the students final letter grade, one could go back to the
sources documents, the students test papers, to see if any error had been
made during the processing step.
Distribution. This step refers to the distribution of the output data. Recordings
of the output data are often called report documents. For example, the report
document in the case of student grades is the class grade sheet which is
forwarded to the registrar. The flow line which goes from the distribution box
back to the originating box indicates that report documents may become the
source documents for data processing.
Storage. Storage is crucial in many data processing procedures. Data
processing results are frequently placed in the storage to be used as input
data for further processing at a later date. The two flow lines between the
processing box and storage box indicate the interaction of these two steps. A
unified set of data in storage is called a file. Usually a file consists of a
collection of records, where each record contains similar data items, and a
collection of related files is called a data base.