The V model is a variant of the waterfall approach to software development. It consists of four phases: descending, base, ascending, and across the gap. In the descending phase, requirements are specified and designs are developed. In the base, code modules are produced. The ascending phase involves testing at various levels from module to integration to system. Finally, the "across the gap" phase uses the descending artifacts to develop test plans and criteria to test the software and ensure it meets requirements.

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V model of development
A VARIANT OF THE WATERFALL APPROACH
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Overview The V model has 4 areas
 Descending
Specify requirements and specifications
 Base
Develop code modules
 Ascending
Testing
 Across the gap
Use descending topics to build test criteria & plans
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Requirements
definition
Requirements
specification
Customer
requirements
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Initial Client requirements will have been analysed, reviewed against
existing systems and proposed systems given to the client for
consideration.
The Requirements Definition and Requirements Specification are
created by the team on their understanding of the client requirements.
If correct the client acceptance will be the commencement of the project
development otherwise a refinement process will need to take place

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High level
design
Requirements
definition
Requirements
specification
Customer
requirements
Acceptance
criteria
Develop/ Agree
acceptance
criteria
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The clients agreement of the Requirements Specification
means the DELIVERABLES have been identified. These
are used to produce the ACCEPTANCE Criteria
Possibly at the same time, if the team has sufficient staff,
the high level design is being produced. By knowing
what the Acceptance Criteria are, the design is built
towards that.

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Low Level
design
High level
design
Requirements
definition
Technical
specification
Requirements
specification
Customer
requirements
Acceptance
criteria
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
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System testing
Integration testing
Tech spec may affect system test
plan

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
Vmodelofdevelopment
73We now have the descending part of the V. From this the
links across to the ascending side provide much of the evidence
needed to show the completion of the project,

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Module testing
Developed
modules
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
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The base of the V is the development,
or coding, of the Modules, followed
by Testing, developed from the
Descending side
Tested
modules

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Integrate and
test
Module testing
Tested
modules
Integrated
system
Developed
modules
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
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Using the integration plan
from the left side,
integration testing and
reports are produced

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Integrate and
test
Module testing
System testing
Tested
modules
Integrated
system
Tested system
Developed
modules
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
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103Systems Testing is
from the CLIENT and
covers functionality,
interdependency and
communication.
functional and non-
functional
requirements

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Integrate and
test
Module testing
System testing
Tested
modules
Integrated
system
Tested system
Developed
modules
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
Vmodelofdevelopment
113Ascending side of the V
model is now completed.

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Low Level
design
Module
production
High level
design
Requirements
definition
Module
specification
Technical
specification
Requirements
specification
Customer
requirements
Integrate and
test
Module testing
System testing
Customer
acceptance
Tested
modules
Integrated
system
Tested system
Accepted System
Developed
modules
Acceptance
criteria
Module test
plan
Integration
test plan
test plan
Develop/ Agree
acceptance
criteria
Generate
system test
plan
Produce
integration test
plan
Produce
module test
plan
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Customer completes final acceptance steps
and accepts delivery of the system

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Issues & Problems
 A variant of the Waterfall model.
 Tests developed from analysis elements.
 Not “responsive” as Agile or Scrum.
 Provides good evidence for compliance requirements.
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