Software Development Life Cycle Models

SDLC Models

• SDLC (Software Development Life Cycle) models are defined and designed to be followed during the software development process.
• Each process model follows a series of steps unique to its type to ensure success in the software development process.

Waterfall Model

• The earliest SDLC approach used for software development.
• A linear sequential life cycle model where each phase must be completed before the next phase can begin, with no overlapping phases.
• Phases:
  • Requirement gathering and analysis
  • System design
  • Implementation
  • Testing
  • Deployment
  • Maintenance
• Application:
  • Suitable for projects with well-defined, clear, and fixed requirements.
  • Technologies are well understood and not dynamic.
  • Ample resources with required expertise are available.
  • Short projects.
• Advantages:
  • Simple and easy to understand and use.
  • Easy to manage.
  • Well-defined stages.
  • Well-understood milestones.
  • Easy to arrange tasks.
  • Process and results are well-documented.
• Disadvantages:
  • No working software is produced until late in the life cycle.
  • High amounts of risk and uncertainty.
  • Not suitable for complex and object-oriented projects.
  • Poor model for long and ongoing projects.

Iterative Model

• Combines iterative development with the systematic controlled aspects of the waterfall model.
• Phases:
  • Requirements
  • Design
  • Implementation
  • Testing
• Iterative development process model that does not attempt to start with a full specification of requirements.
• Application:
  • Suitable for projects with clearly defined and understood requirements.
  • Major requirements must be defined, but some functionalities may evolve with time.
  • Time-to-market constraint.
  • New technology is being used and learned by the development team.
  • Resources with needed skill sets are not available.
• Advantages:
  • Working functionality can be developed quickly and early in the life cycle.
  • Results are obtained early and periodically.
  • Parallel development can be planned.
  • Progress can be measured.
  • Less costly to change scope and requirements.
  • Testing and debugging are easier.
• Disadvantages:
  • More resources may be required.
  • Not suitable for changing requirements.
  • More management attention is required.
  • System architecture or design issues may arise.
  • Defining increments may require definition of the complete system.

Spiral Model

• Combines the idea of iterative development with the systematic controlled aspects of the waterfall model.
• Phases:
  • Identification
  • Design
  • Construct or build
  • Evaluation and risk analysis
• Application:
  • Suitable for projects with medium to high risk.
  • Long-term project commitment.
  • Requirements are complex and need evaluation.
  • New product line released in phases.
  • Significant changes are expected during the development cycle.
• Advantages:
  • Changing requirements can be accommodated.
  • Allows extensive use of prototypes.
  • Requirements can be captured more accurately.
  • Users see the system early.
  • Development can be divided into smaller parts.
  • Risky parts can be developed earlier.
• Disadvantages:
  • Management is more complex.
  • End of the project may not be known early.
  • Not suitable for small or glorious projects.
  • Could be expensive for small projects.
  • Process is complex.
  • Spiral may go on indefinitely.

V Model

• An extension of the waterfall model.
• Execution of processes happens in a sequential manner in a V shape.
• Phases:
  • Verification
  • Validation
• Verification phases:
  • Business requirement analysis
  • System design
  • Architectural design
  • Module design
• Validation phases:
  • Unit testing
  • Integration testing
  • System testing
  • Acceptance testing
• Application:
  • Suitable for projects with well-defined and fixed requirements.
  • Medical development field.
  • Requirements are well understood and documented.
  • Technology is not dynamic.
  • Project is short.
• Advantages:
  • Highly disciplined model.
  • Simple and easy to understand and use.
  • Easy to manage.
  • Works well for smaller projects.
• Disadvantages:
  • High risk and uncertainty.
  • Not suitable for complex and object-oriented projects.
  • Poor model for long and ongoing projects.
  • Not suitable for projects where requirements are at a moderate to high risk of changing.

Big Bang Model

• An SDLC model where no specific process is followed.
• Phases:
  • Development and coding
• Application:
  • Suitable for small projects with one or two developers.
  • Ideal for academic or practice projects.
  • Requirements are not well understood.
  • No final release date is given.
• Advantages:
  • Simple model.
  • Little or no planning required.
  • Easy to manage.
  • Gives flexibility to developers.
• Disadvantages:
  • High risk and uncertainty.
  • Not suitable for complex and object-oriented projects.
  • Poor model for long and ongoing projects.
  • Can turn out to be very expensive if requirements are misconceived.### Agile Model
• Agile model is a combination of iterative and incremental process models, focusing on process adaptability and customer satisfaction through rapid delivery of working software products.
• Agile methods break the product into small incremental builds, with each iteration lasting from one to three weeks.
• Cross-functional teams work simultaneously on various areas like planning, requirement analysis, design, coding, unit testing, and acceptance testing.
• At the end of each iteration, a working product is displayed to the customer and important stakeholders.
• Agile believes that every project needs to be handled differently, and existing methods need to be tailored to suit the project requirements.
• Tasks are divided into time boxes or small time frames to deliver specific features for a release.
• Agile manifesto principles include individuals and interactions, self-organization and motivation, working software demo, customer collaboration, and responding to change.
• Agile is based on adaptive software development methods, unlike traditional SDLC models which are based on predictive approaches.

Advantages of Agile Model

• Realistic approach to software development
• Promotes teamwork and cross-training
• Functionality can be developed rapidly and demonstrated
• Resource requirements are minimum
• Suitable for fixed or changing requirements
• Delivers early partial working solutions
• Good model for environments that change steadily
• Minimal rules, documentation, and planning required
• Enables concurrent development and delivery within an overall planned context

Disadvantages of Agile Model

• Not suitable for handling complex dependencies
• More risks of sustainability, maintainability, and extensibility
• An overall plan, agile leader, and practice are required
• Strict delivery management dictates the scope and functionality to be delivered
• Depends heavily on customer interaction
• High individual dependency
• Transfer of technology to new team members may be challenging due to lack of documentation

RAD Model

• RAD (Rapid Application Development) model is based on prototyping and iterative development with no specific planning involved.
• It focuses on gathering customer requirements through workshops or focus groups.
• Early testing of prototypes by the customer using iterative concept.
• Reuse of existing prototypes or components and continuous integration and rapid delivery.
• RAD projects follow iterative and incremental models, with small teams comprising developers, domain experts, customer representatives, and other IT resources working progressively on their component or prototype.

RAD Model Design

• Business modeling: designing the business model for the product under development in terms of flow of information and distribution of information between various business channels.
• Data modeling: reviewing and analyzing the information gathered in the business modeling phase to form sets of data objects vital for the business.
• Process modeling: converting the data object sets defined in the data modeling phase to establish the business information flow needed to achieve specific business objectives.
• Application generation: building the actual system using automation tools to convert process and data models into actual prototypes.

Advantages of RAD Model

• Changing requirements can be accommodated
• Progress can be measured
• Iteration time can be short with the use of powerful RAD tools
• Productivity with fewer people in a short time
• Reduced development time
• Increases reusability of components
• Quick initial reviews occur
• Encourages customer feedback
• Integration from the very beginning solves a lot of integration issues

Disadvantages of RAD Model

• Dependency on technically strong team members for identifying business requirements
• Only systems that can be modularized can be built using RAD
• Requires highly skilled developers or designers
• High dependency on modeling skills
• Inapplicable to cheaper projects as costs of modeling and automated code generation is very high
• Management complexity is more
• Suitable for systems that are component-based and scalable
• Requires user involvement throughout the life cycle
• Suitable for a project requiring shorter development times

SDLC Models

• SDLC models are designed to ensure success in the software development process, with each process model following a series of unique steps.

Waterfall Model

• A linear sequential life cycle model with no overlapping phases.
• Phases include requirement gathering, system design, implementation, testing, deployment, and maintenance.
• Suitable for projects with well-defined, clear, and fixed requirements, well-understood technology, and ample resources.
• Advantages include simplicity, ease of management, and well-defined stages.
• Disadvantages include no working software produced until late in the life cycle, high risk, and unsuitability for complex and long projects.

Iterative Model

• Combines iterative development with the systematic controlled aspects of the waterfall model.
• Phases include requirements, design, implementation, and testing.
• Suitable for projects with clearly defined requirements, time-to-market constraints, and new technology.
• Advantages include quick development of working functionality, early and periodic results, and easier testing and debugging.
• Disadvantages include resource requirements, unsuitability for changing requirements, and potential system architecture issues.

Spiral Model

• Combines iterative development with the systematic controlled aspects of the waterfall model.
• Phases include identification, design, construct or build, and evaluation and risk analysis.
• Suitable for projects with medium to high risk, long-term commitments, and complex requirements.
• Advantages include accommodation of changing requirements, extensive use of prototypes, and accurate requirement capture.
• Disadvantages include complex management, unknown project end, and unsuitability for small projects.

V Model

• An extension of the waterfall model with a V-shaped execution of processes.
• Phases include verification and validation.
• Verification phases include business requirement analysis, system design, architectural design, and module design.
• Validation phases include unit testing, integration testing, system testing, and acceptance testing.
• Suitable for projects with well-defined and fixed requirements, well-understood technology, and short projects.
• Advantages include simplicity, ease of management, and well-defined stages.