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IBM Global Services – Testing Competency

Software Life Cycles

© Copyright IBM Corporation 2006
14/12/2006 IBM Confidential


Need of Software Life Cycle Models

For More complex systems
 More features
 More sophistication leads greater complexity
 More chances of error prone without proper plan/cycle.

To overcome the above criteria we need systematic approach which are nothing but
software Life Cycle Models.

2 IBM Confidential © Copyright IBM Corporation 2005


Various Software Life Cycle Models
Software life cycle models describe various phases of the software cycle and the order
in which those phases are executed. There are tons of models, and many companies
adopt their own, but all have very similar patterns. Some of the models as follows.

 General Model

• Water fall model/ Linear Sequential/ Classic Life Cycle Model
• V-Model
• Rapid Application Development (RAD) model
• Incremental Model
• Spiral Model
• Proto type model
• Fourth Generation (4GT) Techniques



General Life Cycle Model
Software life cycle models describe phases of the software cycle and the order in
which those phases are executed. There are tons of models, and many companies
adopt their own, but all have very similar patterns. The general, basic model is shown
below

Requirements System
Analysis Design
Coding Testing Delivery

System/information
Engineering



Water fall / Linear Sequential /Classic Life Cycle Model

The "waterfall model", documented in 1970 by Royce was the first publicly documented
life cycle model. The model was developed to help with the increasing complexity of
aerospace products.
This is the most common and classic of life cycle models, also referred to as a linear-
sequential life cycle model. It is very simple to understand and use. In a waterfall
model, each phase must be completed in its entirety before the next phase can begin.
At the end of each phase, a review takes place to determine if the project is on the
right path and whether or not to continue or discard the project. Unlike what I
mentioned in the general model, phases do not overlap in a waterfall model.
The least flexible and most obsolete of the life cycle models. Well suited to projects
that has low risk in the areas of user interface and performance requirements, but high
risk in budget and schedule predictability and control.



Water fall model

Requirements
Specification

System
design

Coding

Testing

Delivery



Water fall model (contd.)
Advantages
 Simple and easy to use.
 Easy to manage due to the rigidity of the model – each phase has specific
deliverables and a review process.
 Phases are processed and completed one at a time.
 Works well for smaller projects where requirements are very well understood/stable.
Disadvantages
 It’s difficult to respond to changing customer requirements.
 Adjusting scope during the life cycle can kill a project
 No working software is produced until late during the life cycle.
 High amounts of risk and uncertainty.
 Poor model for complex and object-oriented projects.
 Poor model for long run and ongoing projects.



V - model

 Another variant of the waterfall model — the V-model — associates each development
activity with a test or validation at the same level of abstraction. Each development
activity builds a more detailed model of the system than the one before it, and each
validation tests a higher abstraction than its predecessor.

 The least flexible and most obsolete of the life cycle models. Well suited to projects that
has low risk in the areas of user interface and performance requirements, but high risk
in budget and schedule predictability and control.



V - model (contd.)

System System
Requirements
Test Plan Testing

High Level Integration Integration
Design Test Plan Testing
Ve
St

r if i
ati

ca

Low level Module Level Module Level

Te r)
cT

t io

g
(o

in
n(

Design Test Plan Testing
es

n

st
tio
or)
t in

Dy ida

ic
g

l

m
Va

na
Code &
Unit test



V - model (contd.)
Advantages
 Simple and easy to use.
 Each phase has specific deliverables.
 Higher chance of success over the waterfall model due to the development of test
plans early on during the life cycle.
 Works well for small projects where requirements are easily understood.
Disadvantages
 Very rigid, like the waterfall model.
 Little flexibility and adjusting scope is difficult and expensive.
 Software is developed during the implementation phase, so no early prototypes of the
software are produced.
 Model doesn’t provide a clear path for problems found during testing phases.



Incremental/Iterative model
This model does not attempt to start with full specification of requirements. Multiple
development cycles take place here, making the life cycle a “multi-waterfall” cycle.
Cycles are divided up into smaller, more easily managed iterations. Each iteration
passes through the requirements, design, implementation and testing phases.
A working version of software is produced during the first iteration, so you have working
software early on during the software life cycle. Subsequent iterations build on the
initial software produced during the first iteration.

Key Points
 Development and delivery is broken down into increments
 Each increment delivers part of the required functionality
 Requirements are prioritised and the highest priority requirements are included in early
increments
 Once the development of an increment is started, the requirements are frozen
 Requirements for later increments can continue to evolve



Incremental/Iterative model (contd.)
Increment 1

System Delivery of 1st
Analysis Coding Testing Increment
Design

System Delivery of 2nd
Increment 2 Analysis Coding Testing Increment
Design
No. of increments

System Delivery of 3rd
Increment 3 Analysis Coding Testing Increment
Design

Time



Incremental/Iterative model (contd.)
Advantages
 System functionality is available earlier and customer does not have to wait as long.
 Early increments act as a prototype to help elicit requirements for later increments.
 The highest priority functionalities tend to receive more testing.
 More flexible – less costly to change scope and requirements.
 Easier to test and debug during a smaller iteration.
 Easier to manage risk because risky pieces are identified and handled during its
iteration.
 Each iteration is an easily managed milestone.
Disadvantages
 Each phase of an iteration is rigid and do not overlap each other.
 Problems may arise pertaining to system architecture because not all requirements are
gathered up front for the entire software life cycle.



Prototype model

In this model, a prototype (an early approximation of a final system or product) is built,
tested, and then reworked as necessary until an acceptable prototype is finally achieved
from which the complete system or product can now be developed.
Prototype paradigm begins with requirements gathering. Developer and customer meet
and define the overall objectives for the software, identify whatever requirements are
known, and outline areas where further definition is mandatory.
A quick design occurs which leads to the construction of prototype.
The prototype is evaluated by the customer/user and used to refine the requirements for
the software to be developed.
Iteration occurs as the prototype is tuned to satisfy the user requirements, while at the
same time enabling developer to better understand what needs to be done.



Prototype model

Begin
Begin Listen to
Listen to Build
Build
Prototype
Prototype
Client/user
Client/user

Client
Client
evaluates the
evaluates the
prototype
prototype
Prototype used for
 Understanding the requirements for the user interface
 Examining feasibility of a proposed design approach
Disadvantages
 Users treat the prototype as the solution
 A prototype is only a partial solution



Spiral - model
 Presented by Boehm in 1985. The spiral model is focused on risk management.
 This model of development combines the features of the prototyping model and the
waterfall model. The spiral model is favored for large, expensive, and complicated
projects.
 The spiral model is similar to the incremental model, with more emphases placed on risk
analysis. The spiral model has four phases: Planning, Risk Analysis, Engineering and
Evaluation. A software project repeatedly passes through these phases in iterations
(called Spirals in this model). The baseline spiral, starting in the planning phase,
requirements is gathered and risk is assessed. Each subsequent spiral builds on the
baseline spiral.
 Requirements are gathered during the planning phase. In the risk analysis phase, a
process is undertaken to identify risk and alternate solutions. A prototype is produced at
the end of the risk analysis phase.
 Software is produced in the engineering phase, along with testing at the end of the
phase. The evaluation phase allows the customer to evaluate the output of the project to
date before the project continues to the next spiral.
 In the spiral model, the angular component represents progress, and the radius of the
spiral represents cost.



Spiral – model (contd.)

Planning
Planning Risk
Risk
Analysis
Analysis

Go/No-Go
Decision

Evaluation Development
Development
Evaluation



Spiral – model (contd.)
Advantages
 High amount of risk analysis.
 Risks are explicitly assessed and resolved throughout the process
 Focus on early error detection and design flaws.
 Good for large and mission-critical projects.
 Software is produced early in the software life cycle.
Disadvantages
 Can be a costly model to use.
 Risk analysis requires highly specific expertise.
 Project’s success is highly dependent on the risk analysis phase.
 Doesn’t work well for smaller projects.



Rapid Application Development (RAD) model

RAD model makes heavy use of reusable software components with an extremely short
development cycle.
The RAD is a linear sequential software development process that emphasizes an
extremely short development cycle. The RAD software model is a "high speed"
adaptation of the linear sequential model in which rapid development is achieved by
using a component-based construction approach. Used primarily for information systems
applications, the RAD approach encompasses the following phases
 Business modeling
 Data modeling
 Process modeling
 Application generation
 Testing
RAD process emphasizes reuse many of the program components have already been
tested, which minimizes the testing and development time.



Fourth Generation (4GT) Techniques

Software tool is used to generate the source code automatically for a software
system from a high level specification representation. This is latest technique.


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