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About SDLC Models
Software Development Life Cycle ( also called SDLC Models ) is a workflow process
which defines the core stages and activities of development cycles or A framework
that describes the operations performed at each phase of a software development
project.
SDLC Models
The SDLC aims to produce high-quality software that meets or exceeds customer
expectations, reaches completion within times and cost estimates.
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Some of the SDLC Models are as follows
â˘Waterfall Model
â˘Incremental SDLC Model
â˘Spiral Model
â˘Evolutionary Prototyping Model
â˘Agile Model
â˘RAD Model
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1) Waterfall Model
â˘It is one of the oldest and most well-known SDLC models
â˘It follows a sequential step-by-step process from requirements analysis to
maintenance.
â˘Systems that have well-defined and understood requirements are a good fit for the
Waterfall Model
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Waterfall Model Strong Points
â˘Easy to understand, easy to use
â˘Provides structure to inexperienced staff
â˘Milestones are well understood
â˘Sets requirements stability
â˘Good for management control (plan, staff, track)
â˘Works well when quality is more important than cost or schedule
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Limitation of the Waterfall Model
â˘Not suitable for the project where requirements are changing.
â˘The high amount of risk and uncertainty
â˘Not good for the object-oriented project
â˘Poor model for long and ongoing project
â˘Can give a false impression of progress
â˘Integration is one big bang at the end
â˘Little opportunity for the customer to preview the system
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Suitable Situation to use Waterfall Model
â˘Work well for a small project
â˘When Requirements are very well known
â˘When Product definition is stable
â˘When Technology is understood
â˘When New version of an existing product
â˘When Porting a current product to a new platform.
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2) Incremental SDLC Model
â˘In this model, it constructs a partial implementation of a total system that is divide
project into builds then slowly add functionality in each build.
â˘The incremental model prioritizes the requirements of the system and then
implements them in groups.
â˘Each subsequent release of the system adds function to the previous version until
all designed functionality has been implemented.
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Incremental Model Strong Points
â˘Develop high-risk or major functions first
â˘Each release delivers an operational product
â˘The customer can respond to each build
â˘Uses âdivide and conquerâ breakdown of tasks
â˘Lowers initial delivery cost
â˘Initial product delivery is faster
â˘Customers get important functionality early
â˘Risk of changing requirements is reduced
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Incremental Model Limitations
â˘Requires good planning and design
â˘Needs an early definition of a complete and fully functional system to allow for the
definition of increments
â˘Well-defined module interfaces are required (some will be developed long before
others)
â˘The total cost of the complete system is higher than the waterfall model
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Suitable Situation to use Incremental Model
â˘Risk, funding, schedule, program complexity, or need for early realization of
benefits.
â˘Most of the requirements are known up-front but are expected to evolve over
time
â˘A need to get basic functionality to the market early
â˘On projects which have lengthy development schedules
â˘On a project with new technology
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3) Spiral SDLC Model
â˘It is a ârisk-drivenâ iterative model
â˘It divides a project into iterations
â˘Each iteration deals with 1 or more risks
â˘Each iteration starts with a small set of requirements and goes through the
development phase (except Installation and Maintenance) for those set of
requirements.
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Spiral Model Strong Points
â˘It provides an early indication of insurmountable risks, without much cost
â˘Development phases can be determined by the project manager, according to the
complexity of the project.
â˘Users can be closely tied to all lifecycle steps and can see the system early because
of rapid prototyping tools
â˘Project monitoring is very effective. Each phase requires a review from concerned
people (Early and frequent feedback from users). This makes the model more
transparent. The design does not have to be perfect
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â˘Estimates such as budget and schedule become more realistic as work progressed
because important issues are discovered earlier.
â˘Manages risks and develops the system into phases.
â˘Changes can be introduced later in the life cycle as well.
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Spiral Model Limitations
â˘Time spent on evaluating risks too substantial for small or low-risk projects
â˘Time spent planning, resetting objectives, doing risk analysis and prototyping may be
excessive
â˘The model is complex
â˘Risk assessment expertise is required
â˘Spiral may continue indefinitely
â˘Maybe hard to define the objective, verifiable milestones that indicate readiness to
proceed through the next iteration
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â˘High cost and time to reach the final product.
â˘Needs special skills to evaluate the risks and assumptions.
Suitable Situation to use Spiral Model
â˘When the creation of a prototype is appropriate
â˘When costs and risk evaluation is important
â˘For medium to high-risk projects
â˘For Long-term project commitment unwise because of potential changes to economic
priorities
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â˘When users are unsure of their needs
â˘When requirements are complex
â˘For New product line
â˘When Significant changes are expected (research and exploration)
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4)Evolutionary Prototyping Model
â˘Developers build a prototype during the requirements phase
â˘The prototype is evaluated by end users
â˘Users give corrective feedback
â˘Developers further refine the prototype
â˘When the user is satisfied, the prototype code is brought up to the standards needed
for a final product.
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Steps in Prototyping SDLC Models
â˘A preliminary project plan is developed
â˘A partial high-level paper model is created
â˘The model is a source for a partial requirements specification
â˘A prototype is built with basic and critical attributes
â˘The designer builds the database, user interfaces, and algorithmic functions
â˘The designer demonstrates the prototype, the user evaluates for problems and
suggests improvements.
â˘This loop continues until the user is satisfied
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Evolutionary Prototyping SDLC Models Strong Points
â˘Requires user involvement
â˘Customers can âseeâ the system requirements as they are being gathered.
â˘Developers learn from customers
â˘Reduce the development time
â˘Reduce the development cost
â˘Unexpected requirements accommodated
â˘Allows for flexible design and development
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â˘Missing functionalities can be easily added
â˘Result in higher user satisfaction
Evolutionary Prototyping SDLC Models Limitations
â˘Too much involvement of the customer
â˘Insufficient analysis
â˘The design is of less quality
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â˘The resulting system is harder to maintain. Overall maintainability may be
overlooked
â˘A prototype is a quick-and-dirtyâ solution
â˘The customer may want the prototype delivered.
â˘The process may continue forever
â Learn Business Analyst Training â
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Suitable Situation to use Evolutionary Prototyping SDLC
Models
â˘When requirements are unstable or must be clarified
â˘For developing user interfaces
â˘For Short-lived demonstrations
â˘For the new, original development
â˘With the analysis and design portions of object-oriented development.
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5)Agile Model
â˘The biggest problem with software development is changing requirements
â˘Agile processes accept the reality of change versus the hunt for complete, rigid
specifications
â˘Speed up or bypass one or more life cycle phases
â˘Usually less formal and reduced scope
â˘Used for time-critical applications
â˘Used in organizations that employ disciplined methods
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Agile Model Strong Points
â˘It can adapt well with changing requirement
â˘Deliver a working product faster than a conventional linear development model
â˘Customer feedback at every stage ensures that the end deliverable satisfies their
expectations
â˘No guesswork between the development team and the customer, as there is face
to face communication and continuous inputs from the client
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â˘Decrease the time required to avail some system features.
â˘A test can be conducted during the design cycle
â˘Fewer risks and has more flexibilities
â˘Modification in the system needs less time
â˘The result is high-quality software in the least possible time duration and
satisfied customer.
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Agile Model Limitations
â˘More Programmer centric than user-centric
â˘For larger projects, it is difficult to judge the efforts and the time required for the
project in the SDLC.
â˘Since the requirements are ever-changing, there is hardly any emphasis, which is
laid on designing and documentation. Therefore, chances of the project going off
the track easily are much more
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â˘Scalability
â˘The ability and collaboration of the customer to express user needs.
â˘Documentation is done at later stages.
â˘Reduce the usability of components.
â˘Needs special skills for the team.
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Rapid Application Development Model (RAD)
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Phases in the RAD model are as follows,
â˘Requirements planning phase â a workshop utilizing structured discussion of
business problems
â˘User description phase â automated tools capture information from users
â˘Construction phase â productivity tools, such as code generators and screen
generators
â˘Cutover phase â installation of the system, user acceptance testing and user
training
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RAD Model Strong Points
â˘Reduced cycle time and improved productivity with fewer people means lower costs
â˘Time-box approach mitigates cost and schedule risk
â˘It increases the reusability components
â˘Greater customer satisfaction
â˘Fast delivery time
â˘Reduce the development time
â˘The focus moves from documentation to code (WYSIWYG).
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â˘Uses modeling concepts to capture information about business, data, and processes.
RAD Model Limitations
â˘Large manpower is required to create the number of RD teams.
â˘Risk of never achieving closure
â˘Hard to use with legacy systems
â˘Requires a system that can be modularized
â˘Require highly skilled developer and designer.
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â˘Not useful when technical risks are high
â˘Developers and customers must be committed to rapid-fire activities in an
abbreviated time frame.
Suitable Situation to use RAD Model
â˘Reasonably well-known requirements
â˘The user involved throughout the life cycle
â˘The project can be time-boxed
â˘Functionality delivered in increments
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â˘High performance not required
â˘Low technical risks
â˘The system can be modularised
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