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.

Some of the SDLC Models are as follows

• Waterfall Model
• Incremental SDLC Model
• Spiral Model
• Evolutionary Prototyping Model
• Agile Model
• RAD Model

1) Waterfall Model 

• It is one of the oldest and most well-known SDLC models
• It follows a sequential step-by-step process from requirements analysis to maintenance.
• Systems that have well-defined and understood requirements are a good fit for the Waterfall Model

Waterfall Model Strong Points

• Easy to understand, easy to use
• Provides structure to inexperienced staff
• Milestones are well understood
• Sets requirements stability
• Good for management control (plan, staff, track)
• Works well when quality is more important than cost or schedule

Limitation of the Waterfall Model

• Not suitable for the project where requirements are changing.
• The high amount of risk and uncertainty
• Not good for the object-oriented project
• Poor model for long and ongoing project
• Can give a false impression of progress
• Integration is one big bang at the end
• Little opportunity for the customer to preview the system 

Suitable Situation to use Waterfall Model

• Work well for a small project
• When Requirements are very well known
• When Product definition is stable
• When Technology is understood
• When New version of an existing product
• When Porting a current product to a new platform. 

2) Incremental SDLC Model

• 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.
• The incremental model prioritizes the requirements of the system and then implements them in groups.
• Each subsequent release of the system adds function to the previous version until all designed functionality has been implemented.

Incremental Model Strong Points

• Develop high-risk or major functions first
• Each release delivers an operational product
• The customer can respond to each build
• Uses “divide and conquer” breakdown of tasks
• Lowers initial delivery cost
• Initial product delivery is faster
• Customers get important functionality early
• Risk of changing requirements is reduced

Incremental Model Limitations

• Requires good planning and design
• Needs an early definition of a complete and fully functional system to allow for the definition of increments
• Well-defined module interfaces are required (some will be developed long before others)
• The total cost of the complete system is higher than the waterfall model

Suitable Situation to use Incremental Model

• Risk, funding, schedule, program complexity, or need for early realization of benefits.
• Most of the requirements are known up-front but are expected to evolve over time
• A need to get basic functionality to the market early
• On projects which have lengthy development schedules
• On a project with new technology

3) Spiral SDLC Model

• It is a “risk-driven” iterative model
• It divides a project into iterations
• Each iteration deals with 1 or more risks
• Each iteration starts with a small set of requirements and goes through the development phase (except Installation and Maintenance) for those set of requirements.

Spiral Model Strong Points

• It provides an early indication of insurmountable risks, without much cost
• Development phases can be determined by the project manager, according to the complexity of the project.
• Users can be closely tied to all lifecycle steps and can see the system early because of rapid prototyping tools
• 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
• Estimates such as budget and schedule become more realistic as work progressed because important issues are discovered earlier.
• Manages risks and develops the system into phases.
• Changes can be introduced later in the life cycle as well.

Spiral Model Limitations

• Time spent on evaluating risks too substantial 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
• Maybe hard to define the objective, verifiable milestones that indicate readiness to proceed through the next iteration
• High cost and time to reach the final product.
• Needs special skills to evaluate the risks and assumptions.

Suitable Situation to use Spiral Model

• When the creation of a prototype is appropriate
• When costs and risk evaluation is important
• For medium to high-risk projects
• For Long-term project commitment unwise because of potential changes to economic priorities
• When users are unsure of their needs
• When requirements are complex
• For New product line
• When Significant changes are expected (research and exploration) 

4)Evolutionary Prototyping Model

• Developers build a prototype during the requirements phase
• The prototype is evaluated by end users
• Users give corrective feedback
• Developers further refine the prototype
• When the user is satisfied, the prototype code is brought up to the standards needed for a final product.

Steps in Prototyping SDLC Models

• A preliminary project plan is developed
• A partial high-level paper model is created
• The model is a source for a partial requirements specification
• A prototype is built with basic and critical attributes
• The designer builds the database, user interfaces, and algorithmic functions
• The designer demonstrates the prototype, the user evaluates for problems and suggests improvements.
• This loop continues until the user is satisfied

Evolutionary Prototyping SDLC Models Strong Points

• Requires user involvement
• Customers can “see” the system requirements as they are being gathered
• Developers learn from customers
• Reduce the development time
• Reduce the development cost
• Unexpected requirements accommodated
• Allows for flexible design and development
• Missing functionalities can be easily added
• Result in higher user satisfaction

Evolutionary Prototyping SDLC Models Limitations

• Too much involvement of the customer
• Insufficient analysis
• The design is of less quality
• The resulting system is harder to maintain. Overall maintainability may be overlooked
• A prototype is a quick-and-dirty” solution
• The customer may want the prototype delivered.
• The process may continue forever

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Suitable Situation to use Evolutionary Prototyping SDLC Models

• When requirements are unstable or must be clarified
• For developing user interfaces
• For Short-lived demonstrations
• For the new, original development
• With the analysis and design portions of object-oriented development.

5)Agile Model

• The biggest problem with software development is changing requirements
• Agile processes accept the reality of change versus the hunt for complete, rigid specifications
• Speed up or bypass one or more life cycle phases
• Usually less formal and reduced scope
• Used for time-critical applications
• Used in organizations that employ disciplined methods

Agile Model Strong Points

• It can adapt well with changing requirement
• Deliver a working product faster than a conventional linear development model
• Customer feedback at every stage ensures that the end deliverable satisfies their expectations
• No guesswork between the development team and the customer, as there is face to face communication and continuous inputs from the client
• Decrease the time required to avail some system features.
• A test can be conducted during the design cycle
• Fewer risks and has more flexibilities
• Modification in the system needs less time
• The result is high-quality software in the least possible time duration and satisfied customer.

Agile Model Limitations

• More Programmer centric than user-centric
• For larger projects, it is difficult to judge the efforts and the time required for the project in the SDLC.
• 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
• Scalability
• The ability and collaboration of the customer to express user needs.
• Documentation is done at later stages.
• Reduce the usability of components.
• Needs special skills for the team.

Rapid Application Development Model (RAD)

Phases in the RAD model are as follows,

• Requirements planning phase – a workshop utilizing structured discussion of business problems
• User description phase – automated tools capture information from users
• Construction phase – productivity tools, such as code generators and screen generators
• Cutover phase – installation of the system, user acceptance testing and user training 

RAD Model Strong Points

• Reduced cycle time and improved productivity with fewer people means lower costs
• Time-box approach mitigates cost and schedule risk
• It increases the reusability components
• Greater customer satisfaction
• Fast delivery time
• Reduce the development time
• The focus moves from documentation to code (WYSIWYG).
• Uses modeling concepts to capture information about business, data, and processes.

RAD Model Limitations

• Large manpower is required to create the number of RD teams.
• Risk of never achieving closure
• Hard to use with legacy systems
• Requires a system that can be modularized
• Require highly skilled developer and designer.
• Not useful when technical risks are high
• Developers and customers must be committed to rapid-fire activities in an abbreviated time frame.

Suitable Situation to use RAD Model

• Reasonably well-known requirements
• The user involved throughout the life cycle
• The project can be time-boxed
• Functionality delivered in increments
• High performance not required
• Low technical risks
• The system can be modularised

Software Development Life Cycle Phases