100 requirements and 60 core requirements in first phase.
20 in next phase
20 in next phase
20 in last phase
The incremental model combines elements of the linear sequential model with
the iterative philosophy of prototyping. The incremental model applies linear
sequences in a staggered fashion as calendar time progresses.
Each
linear sequence produces a deliverable “increment” of the software.
More realistic approach.
For example , word-processing software developed using the
incremental paradigm might deliver basic file management, editing, and document
production functions in the first increment; more sophisticated editing and
document production capabilities in the second increment; spelling and grammar
checking in the third increment; and advanced page layout capability in the
fourth increment.
When an incremental model is used, the
first increment is often a
core product.
That is, basic requirements are addressed, but many supplementary features
(some known, others unknown) remain undelivered.
Incremental development is the process of establishing requirements,
designing, building and testing a system done as a series of smaller
developments.
Advantages
- More realistic approach to development of large scale systems and software.
- Each increment is fully tested before beginning the next.
Drawbacks
- Total planned testing effort would be more than that for waterfall model.
Spiral Model
It came into existence for mission critical projects, where the risk factor
was to be evaluated. Used in Mission Critical System such as guided missile
systems.
Risk Analysis
Critical Software
Risk
Trigger Event
Monitor
Manage
Engineering
Design
Develop
Integration and Testing
While drawing the life cycle, draw it segment by segment.
The spiral model, originally proposed by Boehm is an evolutionary software
process model that couples the iterative nature of prototyping with the
controlled and systematic aspects of the linear sequential model.
It provides the potential for rapid development of incremental versions of
the software.
Using the spiral model, software is developed in a series
of incremental releases. During early iterations, the incremental release might
be a paper model or prototype. During later iterations, increasingly
more complete versions of the engineered system are produced.
The spiral model is intended for large, expensive, risky and
complicated projects. For larger, more critical projects, each task region
contains more work tasks that are defined to achieve a higher level of
formality.
Spiral model that contains six task regions:
•
Planning—tasks required to define resources, timelines,
and other project related information.
•
Risk analysis—tasks required to assess both technical and
management risks.
•
Engineering—tasks required to design, develop, integrate
and test.
•
Customer evaluation—tasks required to obtain customer
feedback based on evaluation of the software representations created during the
engineering stage and implemented during the installation stage.
Advantages:
1. Best for development of Critical applications.
2. Software build is robust in nature.
3. Can cope with the changes in the requirements.
Drawbacks:
1. Time increases.
2. Cost increases, as a new phase is added in the life cycle.
RAD Model
Rapid application development (RAD
), follows the water fall model
itself. Each of the phase of the waterfall model is mapped with
the automation tool. RAD is designed to take advantage of powerful
development software like CASE (Computer Aided Software Engineering) tools,
prototyping tools and code generators (MS Visual Studio, MS Front Page) it is
described as a process through which the development cycle of an application is
expedited. Rapid Application Development thus enables quality products to be
developed in a very short span.
Phase Tool
1. Project Management Project Console
2. Requirements Gathering Requisite Pro
3. Design and Development Rational Rose
4. Test Management QTP, QC, WR
Advantages.
1. Product is operational very soon.
2. Emphasizes on extremely short development life cycle.
3. Requirements are well understood.
4. Creates a fully functional system in a very short span.
5. Component based construction.
Disadvantages
1. High cost to buy the licenses of the RAD tools
Some of these tools costs 10 cr. Client is not going to buy these
expensive tools right.
V MODEL
What was the need of V model?
In earlier SDLC models defects were discovered very late in the life cycle.
Necessity is the mother of invention. Right!!!
What it is?
Implements the waterfall model. Testing is done very early in the Life cycle.
V model emphasis on early discovery of defects, and eventually brings down the
cost.
Requirements 1 <-------------------------------------------> 2 Acceptance Test cases
High Level Design 3 <------------------------------> 4 System Test cases
Low Level Design 5 <-----------------------> 6 Integration Test cases
Unit Level Design 7 <----------> 8 Unit Test cases
9 Code
The ‘V’ can also stand for the terms Verification and Validation.
Advantages:
1. The errors of the particular phases are identified in that particular
phase only. So stops the propagation of defect to another phase. Prevents defect
multiplication.
2. Optimization of the test resources i.e. the testers.
3. Relative reduction on cost compared to the other SDLC models.
4. Starting early means the duration of the life cycle is reduced.
5. Testing activities like test designing start at the beginning of the
project well before coding and therefore saves a huge amount of the project
time.
Verification and Validation model à
V and V model à V model
Some computer illiterates also call it as V shaped model
The waterfall model is a sequential software development model in which development is seen as flowing steadily downwards (like a waterfall). To follow the waterfall model, one proceeds from one phase to the next in a purely sequential manner.
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