Information Technology - The Design Phase: factors to be considered when
designing the input Requirements
The Design Phase: factors to be considered when designing the input
Image. GIGO - Garbage In, Garbage Out!
Having established what the system needs to produce to meet its goals, the
next area of interest is establishing what data needs to be obtained to
produce that output. The design of the input is vital to the successful
creation of a computer system. Put simply, the input must be collected from
the various sources with a minimal amount of errors, and with the greatest
possible speed. A common term used to describe data entry is GIGO - garbage
in, garbage out. This expression highlights the importance of input design
to the quality of the program produced. The final output will only be as
accurate as the data put into the system - and the quality of that data
will be partly determined by the quality of the design of the collection
There are a number of techniques that a good programmer will use to ensure
that the data they collect is of the best quality possible. They will limit
the opportunities for the user to enter the wrong data, and will ensure the
user does not have to enter data twice.
When designing input, the programmer should:
Identify duplicate data - Efficient program design requires that the
program only collect and store each data element once. Programmers should
analyse the data requirements and identify where data is used more than
once and ensure it is collected just once. It is important to do this -
while it may be easier to collect data more than once, rather than create
highly complex data structures, this approach compromises the integrity of
the information produced, as it allows for more input errors and the
creation of conflicting outputs.
Identify methods of reducing input errors - When collecting data, the
programmer should make use of as many of the features available to ensure
that the data being collected is as free from errors as possible. This can
be achieved through the use of features like drop down boxes, radio
buttons, check boxes etc. that limit the user to selecting from pre-defined
"correct" options. By carefully constructing input screens, it is possible
to limit the number of areas the users can enter invalid data.
Identify data validation checks - While it is possible to limit the users
choices to pre-defined choices, it may not always be possible or practical
to do so. An example would be postcodes. While all postcodes are
pre-defined, there are so many of them it would not be possible to list
them all on a screen, so another method must be employed to make sure the
data is accurate. Writing code to check the data is accurate can do this.
For example, the postcodes could be checked to see if they fall within the
expected range for the state given. While this relies on the user to input
correct data, it does reduce the amount of incorrect data the system
Input screen/method design - Thought needs to be given to the actual
design of the input collection screens or methods. Care needs to be taken
to ensure the screens that collect the data are arranged in an attractive
and logical manner. If data is to be entered from a form, then the data
collection screens should follow the general format of those screens to
make data entry easier, and therefore less prone to errors.
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