waterfall spiral

Software Development Life
Lesson Objectives
 To understand the software development life cycle
 To be able to explain what commonly occurs at each stage of the
software development life cycle
 To be able to identify at which stage of the software development life cycle a given
step would occur
 To understand that there are several life cycle models that can be
used (e.g. cyclical, waterfall, spiral)
 To be able to discuss the advantages and disadvantages of these lifecycle models
How is software created?
First comes the idea….everything has to start somewhere…
Requirements /
This is the first and most important step. Questions must be answered
such as:
 Why is the software system required?
 Who is the software system for?
 What must the software system do?
 What are the constraints? (budget/timescale/particular needs)
Now we know what the system is for, we must set about designing it. The
aim being to achieve everything that we established in the previous
phase. Again, more questions will need to be addressed:
 What programming language, operating system or hardware
requirements are there?
 What data is required?
 What file structures are required?
 What user interface is there?
 ….and many more
So now we actually create the software:
 Each step of the design is created using the appropriate technical
 Obviously – need to test it works!
Different Types of Approach
 Spiral / Cyclical
 Waterfall / Sequential
Waterfall and spiral model are different types software development
methodologies. These methodologies assist the developer in building a
system efficiently. Each of the methodologies has a set of rules or
discipline that needs to be followed in order to develop a system. Both of
the methodologies posses their own pros and cons.
Waterfall Model
The waterfall model consists of the usual
main phases, namely:
 Requirements/Analysis
 Design
 Implementation
 Testing
Each phase has its own set of tasks that
should be accomplished by the developer.
The developer must complete each stage
before moving to the next stage in a
sequential manner. Due to this, the
waterfall model is sometimes also referred to
as sequential software development
process. The model approach is from top to
bottom as how a waterfall would flow down.
Spiral Model
Analysis /
(next iteration
planned here)
Spiral Model
The spiral model again contains four main stages. However the
approach is more cyclical as seen in the diagram on the previous slide:
It is an output driven methodology where each circle produces a
prototype better than the previous one.
In the spiral model, it is not necessary for the developer to complete each
stage before moving to another stage. The developer can finish a short
portion in a stage and shift to next stage and then come back again on
next round to finish remaining task in the stages. It is a continuous
process, in which each time the developed application gets more
complex. At the same time the process also gets bigger and bigger.
Waterfall or Spiral?
 Must complete a stage before
moving onto next
 Can work on any stage at any
 No feedback from client until
software delivery
 Constant interaction with client –
feedback and prototype
 Document driven – well planned
in advance (could result in less  More ‘build it’ and see approach
errors at later stages but time
– less advance planning (could
consuming at initial stages)
result in problems – but more
time to fix due to less planning at
 Sequential
 Cyclical
Let’s Play A Game!
 Divide into teams (5 or 6 per team)
 Decide on a team manager
 Team manager to collect challenge resources and info from client
 You have 50 minutes to complete the challenge
Test It!