SDLC Models¶

An SDLC model is a systematic approach to the software development process that defines the stages and tasks involved in building software. It serves as a guide for planning, structuring, and controlling the process of developing information systems.

(i) Waterfall Model¶

• The Waterfall model follows a linear and sequential approach to software development. Each phase in the development process must be completed before moving on to the next one, resembling the downward flow of a waterfall.

flowchart TD
    A[Requirements] --> B[Design]
    B --> C[Implementation/Development]
    C --> D[Verification/Testing]
    D --> E[Deployment]
    E --> F[Maintenance]

Advantages

• Easy to understand and manage
• Suitable for small projects with well-defined requirements at the beginning

Disadvantages

• Inflexible to changes
• Testing happens late
• Limited client feedback
• No early prototypes

(ii) Iterative Model¶

The Iterative model develops a system through repeated cycles (iterations) and in smaller portions at a time.

flowchart TD
    A[Initial Planning/Initialization] --> B[Planning]
    B --> C[Requirements]
    C --> D[Analysis & Design]
    D --> E[Implementation]
    E --> F[Testing]
    F --> G[Evaluation]
    G -->|Next Iteration| B

Advantages

• Early working version
• Flexible to changes
• Risks identified early
• Regular customer feedback
• Better risk management

Disadvantages

• More management complexity
• Needs active customer involvement
• May extend project timeline
• Documentation challenges

(iii) V-Model (Verification and Validation Model)¶

The V-Model extends the waterfall model by emphasizing testing for each corresponding development stage. Each development stage has a directly associated testing phase.

• By integrating verification and validation activities in parallel, this model aims to deliver high-quality software while mitigating the risk of defects.

graph TD
    A[Requirements] --> F[Acceptance Testing]
    B[System Design] --> G[System Testing]
    C[Architecture Design] --> H[Integration Testing]
    D[Module Design] --> I[Module Testing]
    E[Coding]

    A --> B
    B --> C
    C --> D
    D --> E
    F --> G
    G --> H
    H --> I
    I --> E

    style A fill:#f9f,stroke:#333,stroke-width:2px
    style F fill:#f9f,stroke:#333,stroke-width:2px
    style E fill:#444,stroke:#444,stroke-width:2px

Advantages

• Systematic testing
• Clear deliverables
• Easy to manage
• Strong documentation

Disadvantages

• Rigid structure
• No early prototypes
• High cost of testing
• Long development cycle

(iv) Evolutionary Models¶

• Evolutionary Models are iterative.

1. Prototyping Model¶

A software development model where a prototype is built, tested, and refined until it meets client requirements.

flowchart TD
    A[Initial Requirements] --> B[Build Prototype]
    B --> C[Review]
    C --> D[Refine Requirements]
    D -->|Not Satisfied| B
    D -->|Satisfied| E[Development]
    E --> F[Testing]
    F --> G[Maintenance]

Best Used For

• User interface designs
• Online systems
• Web applications
• Mobile apps

Advantages

• Early user feedback
• Clear requirements
• Reduced risk
• Better user satisfaction

Disadvantages

• Time-consuming
• Increased cost
• Client confusion
• Incomplete documentation

2. Spiral Model¶

The Spiral Model combines aspects of both waterfall and prototyping models, emphasizing risk analysis throughout each iteration.

flowchart LR
    subgraph "Iteration 1"
        A1[Planning] --> B1[Risk Analysis]
        B1 --> C1[Engineering]
        C1 --> D1[Evaluation]
        D1 --> A2
    end

    subgraph "Iteration 2"
        A2[Planning] --> B2[Risk Analysis]
        B2 --> C2[Engineering]
        C2 --> D2[Evaluation]
        D2 --> A3
    end

    subgraph "Iteration 3"
        A3[Planning] --> B3[Risk Analysis]
        B3 --> C3[Engineering]
        C3 --> D3[Evaluation]
    end

graph TD
    A[Planning] --> B[Risk Analysis]
    B --> C[Engineering]
    C --> D[Evaluation]
    D --> A

• continuous iteration of the above step....

Four Phases per Spiral

• Planning : Objectives, Alternatives, Constraints, Risk Analysis

• Identify risks: Risk mitigation, Prototyping, Engineering

• Development: Testing, Verification,

• Evaluation: Review results, Plan next iteration, Decision to continue

Best Used For:

• Large, high-risk projects
• Projects needing early user feedback
• Complex systems with unclear requirements Example: New Operating System Development

Advantages

• High risk management
• Early prototypes
• Flexible to changes
• Regular customer feedback

Disadvantages

• Complex management
• High documentation
• Expensive for small projects
• Needs risk assessment expertise

(v) Incremental Model¶

Develops software in increments, with each increment adding new functionality to the previous version.

Development Cycle¶

flowchart TD
        A[Requirements] -->|Build 1| B1[Design]
    subgraph "Increment 1"

        B1 --> C1[Code]
        C1 --> D1[Test]
        D1 --> E1[Release v1]
    end

    subgraph "Increment 2"
        B2[Design] --> C2[Code]
        C2 --> D2[Test]
        D2 --> E2[Release v2]
    end

    A -->|Build 2| B2

Key Features

• Multiple Development Cycles
• Partial Systems
• Prioritized Development
• Parallel Development

Advantages

• Early functional software
• Flexible scheduling
• Easy to test
• Risk management

Disadvantages

• Interface challenges
• Need good planning
• System architecture issues
• Documentation overhead

(vi) Agile Model¶

Agile is an iterative approach that focuses on collaboration, customer feedback, and rapid releases.

Sprint Cycle¶

flowchart TD
    A[Sprint Planning] --> B[Daily Standups]
    B --> C[Development]
    C --> D[Testing]
    D --> E[Sprint Review]
    E --> F[Sprint Retrospective]
    F -->|Next Sprint| A

    style A fill:#f9f,stroke:#333
    style E fill:#f9f,stroke:#333
    style F fill:#f9f,stroke:#333