1 sdlc model

Soft Skills
And
Personality Development

Software
Development Life
Cycle (SDLC)

A framework that describes the activities
performed at each stage of a software
development project.

There are 3 types of SDLC
models
•Waterfall Model
•Iterative Model
•Spiral Model

1.Waterfall Model
• Requirements – defines needed information, function, behavior,
performance and interfaces.
• Design – data structures, software architecture, interface
representations, algorithmic details.
• Implementation – source code, database, user documentation,
testing.
• Test- testing the application for errors so that application
becomes error free
• Maintenance- maintaining the software for additional features

Analysis
Design
Code
Testing
Maintenance

Waterfall Merits and Demerits
Easy to understand, easy to use
Provides structure to
inexperienced staff
Sets requirements stability
Good for management control
(plan, staff, track)
Works well when quality is more
important than cost or schedule
 Inhibits flexibility-Deliverables
created for each phase are
considered frozen, i.e. Customer
has to wait up to last stage for any
modifications.
Can give a false impression of
progress
Little opportunity for customer
to preview the system (until it
may be too late).

When to use the Waterfall
Model
 Requirements are very well known
 Product definition is stable
 Technology is understood
 New version of an existing product
 Porting an existing product to a new platform.
 High risk for new systems because of specification and
design problems.
 Low risk for well-understood developments using familiar
technology.

2. Iterative Enhancement
Model
• It helps to remove the short comings of the
waterfall model
• The phase of the software development remains
the same, but the construction and delivery is
made in repetitive mode
• In the first iteration, a less capable product are
developed and delivered for use and so on

Iteration
1
Iteration
2…
Iteration
n
Release
to client
fig. Iterative Enhancement
Model
Waterfall
model
Basic Model
Product 1
Waterfall
model
Enhanced
Changes
Product 2
Waterfall
model
Enhanced
Changes
Product 3
Finally
Release to
client

Iterative Merits and Demerits
Very Useful when less man
power is required and release
deadlines are tight.
It is best suited for in house
product development.
It is ensured that the user has
something to start with
 Iteration may never end
User may have to endlessly
wait for the final product
The cost estimated is also
high because it is difficult to
relate the software
development cost with the
number of requirements

3.Spiral Model
• In 1988 Boehm developed the spiral model as an iterative model
which includes risk analysis and risk management.
• Here each loop in the spiral represents a phase of the software
process
• Each cycle involves the same sequence of steps as the waterfall
process model
Key idea: on each iteration identify and solve
the sub-problems with the highest risk.

Risk
analysis
Risk
analysis
Risk
analysis
Risk
analysis Proto-
type 1
Prototype 2
Prototype 3
Opera-
tional
protoype
Concept of
Operation
Simulations, models, benchmarks
S/W
requirements
Requirement
validation
Design
V&V
Product
design Detailed
design
Code
Unit test
Integration
testAcceptance
testService Develop, verify
next-level product
Evaluate alternatives
identify, resolve risks
Determine objectives
alternatives and
constraints
Plan next phase
Integration
and test plan
Development
plan
Requirements plan
Life-cycle plan
REVIEW

Spiral Quadrant: Determine
objectives, alternatives and
constraints
• Objectives: functionality,
performance,
hardware/software
interface, critical success
factors, etc.
• Alternatives: build, reuse,
buy, sub-contract, etc.
• Constraints: cost,
schedule, interface, etc.
Spiral Quadrant: Evaluate
alternatives, identify and
resolve risks
• Study alternatives relative to
objectives and constraints
• Identify risks (lack of
experience, new technology,
tight schedules, poor process,
etc.
• Resolve risks (evaluate if
money could be lost by
continuing system
development

• Typical activities:
• Create a design
• Review design
• Develop code
• Inspect code
• Test product
Spiral Quadrant:
Develop next-level
product
Spiral Quadrant:
Plan next phase
• Typical activities
• Develop project plan
• Develop configuration
management plan
• Develop a test plan
• Develop an installation
plan

Spiral Model Strengths
Provides early indication of insurmountable
risks, without much cost
Critical high-risk functions are developed first
The design does not have to be perfect
Users can be closely tied to all lifecycle steps
Early and frequent feedback from users
Cumulative costs assessed frequently

Spiral Model Weaknesses
Time spent for evaluating risks too large for small or low-
risk projects
Time spent planning, resetting objectives, doing risk
analysis and prototyping may be excessive
The model is complex
Risk assessment expertise is required
Spiral may continue indefinitely

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