continued...
Spiral Model is another primitive model.
The spiral model is shown in the figure in the next page.
Ra- requirements analysis of module
A. Similarly with Rb, Rc, Rd.
Da – design of module A. Similarly
with Db, Dc, Dd
Ca – coding of module A. Similarly
with Cb, Cc, Cd
Ta – testing of module A. Similarly
with Tb, Tc, Td
In Spiral model, the software
product is developed in small modules. Let us consider the figure shown below
in developing a s/w product X. X is built by integrating A,B,C and D.
The module A – requirements of the
module is collected first and then the module is designed. The coding of module
A is done after which it is tested for defects and bugs.
The module B – once module A has
been built, we start the same process for module B. But while testing module B,
we test for 3 conditions – a)test module B b)test integration of module B with
A c)test module A.
The module C – after building module
A,B, we start the same process for module C. Here we test for the following
conditions – 1) test module c, b, a 2) test for integration of C and B, C and
A, A and B.
 |
| Spiral Model |
For spiral model, the best example
that we can consider is the MS-Excel application.
The MS-Excel sheet consists of a
number of cells that are the components of Excel sheet.
Here we have to create the cells
first (module A). Then we can do operations on the cells like merge cells into
two , split cell into half (module B ). Then we can draw graphs on the excel
sheet (module C).
Advantages
of Spiral Model :-
1)
Requirement changes are allowed.
2)
After we develop one feature / module of the product, then only we can
go on to develop the next module of the product.
Whenever the customer request for major
changes in requirements in a particular module, then we change only that
module and do testing of both unit and integration of units. This change in
requirements comes up in a separate cycle just to do the changes.
Whenever the customer request minor
changes in the product, then the s/w team makes the minor changes along
with the new module to be developed simultaneously in a single cycle. We don’t
consider making the minor change in a separate cycle of the spiral model due to
time and resource constraints.
The documents collected by Business
analysts during requirement collection stage is known as CRS ( Customer Requirement Specification ) or BRS ( Business Requirement Specification ) or BS ( Business Specification ). In this document , the client
explains how their business works or the requirement of the s/w he needs. The
BA gathers CRS from the client and translates it into SRS ( Software Requirement Specification ). The SRS contains how
the software should be developed and is given by the BA to developers. For more
detailed explanation of how to go about developing the s/w, the BA/developer builds
another document – FS ( Functional
Specification ). FS explains how each and every component should work.
Drawbacks
of Spiral Model – Traditional
model and thus developers only did testing job as well.
Applications
of Spiral Model
- whenever there is dependency in
building the different modules of the software, then we use Spiral Model.
-whenever the customer gives the requirements in stages, we develop the product in stages.
