VEHICLE MANAGEMENT SYSTEM 10081A1215
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SHADAN COLLEGE OF ENGINEERING & TECHNOLOGY Page 24
3.1.2:NON FUNCTIONAL REQUIREMENTS
Nonfunctional requirements are the properties that your product must have. Think of
these properties as the characteristics or qualities that make the product attractive, or usable, or
fast, or reliable. These properties are not required because they are fundamental activities of the
product -- activities such as computations, manipulating data, and so on -- but are there because
the client wants the fundamental activities to perform in a certain manner. They are not part of
the fundamental reason for the product's existence, but are needed to make the product perform
in the desired manner.
Nonfunctional requirements do not alter the product functionality. That is, the
functional requirements remain the same no matter what properties you attach to them. The non-
functional requirements add functionality to the product -- it takes some amount of pressing to
make a product easy to use, or secure, or interactive. However the reason that this functionality is
part of the product is to give it the desired characteristics. So you might think of the functional
requirements as those that do the work, and the nonfunctional requirements as those that give
character to the work.
Nonfunctional requirements make up a significant part of the specification. They are important
as the client and user may well judge the product on its non-functional properties. Provided the
product meets its required amount of functionality, the nonfunctional properties -- how usable,
convenient, inviting and secure it is -- may be the difference between an accepted, well-liked
product, and an unused one.
Let's take a look at another real example. Anyone who has purchased a car, whether they were
aware of it or not, made their final decision based on which car met both their functional and
nonfunctional needs. Functionally, the car had to be able to transport passengers from some
starting location to a particular destination (that is, get me from point A to point B). A variety of
nonfunctional attributes or characteristics were likely considered: security and safety,
maintainability (ease of repair), reliability (probability of failure), scalability (ease of expansion),
efficiency and performance (gas mileage, engine size, capacity -- both in number of passengers
and cargo space), portability (ease of transport -- can it be towed easily or can it tow a trailer),
flexibility (ease of change -- can it adapt to changes in weather/road conditions), and usability
(ease of use -- comfort, handling, stereo sound quality)