Software Development Life Cycle (SDLC)

Software Development Life Cycle (SDLC)

• Software engineering is the systematic process for creating reliable, scalable, and maintainable software, applying engineering principles for functionality, efficiency, and user satisfaction.
• Key activities include:
  • Requirement Gathering: Identifying stakeholder needs and project goals. (Example: Airline ticketing system needs booking, payment, and seat selection).
  • Design: Architecting the system based on requirements. (Example: Layered architecture with presentation, business logic, and database layers).
  • Implementation (Coding): Translating designs into code. (Example: Writing a 'validatePayment()' function in Java or Python).
  • Testing: Verifying the system for bugs and defects. (Example: Testing login functionality with valid and invalid credentials).
  • Maintenance: Updating, enhancing, and fixing software post-deployment. (Example: Adding support for new payment methods like Apple Pay).

Requirements

• Requirements come from:
  • User Needs: Direct input from stakeholders/customers.
  • Industry Standards: Adherence to standards like ISO or GDPR.
  • Client Demands: Specific requests unique to a project.

Subsequent Steps After Requirements

• System Design: Creating diagrams and architecture to outline system structure.
• Implementation Strategy: Defining tools, programming languages, and frameworks.
• Planning for Testing: Determining test strategies (e.g., unit tests, system tests).
• Resource Allocation: Assigning roles to developers, testers, and stakeholders. (Example: E-commerce platform designs order processing workflows using UML diagrams, choosing Python with Django, implementing unit tests for the shopping cart module).

Software Design Concepts

• Experience is crucial in software design:
  • Technical Skills: Choosing best algorithms, tools, and technologies.
  • Problem-Solving Abilities: Finding solutions to constraints.
  • Trade-Off Knowledge: Balancing design considerations like performance vs. security. (Example: Experienced banking app developer prioritizes security over performance using a layered architecture).
• Learn from similar systems:
  • Google: Microservices for scalability.
  • Netflix: Content delivery with regional servers.
  • Spotify: Modular architecture for playlists and streaming.

Architectural Styles

• Layered Architecture: Organizes software into layers (e.g., Presentation, Business Logic, Data Access).
• Pipe-and-Filter Architecture: Data flows sequentially through components (e.g., Compiler System - Lexer, Parser, Evaluator).
• Microservices Architecture: Independent services forming a system (e.g., Netflix - User Service, Recommendation Service, Streaming Service).
• Client-Server Architecture: Divides tasks between clients and servers (e.g., Web browsers interacting with servers).

Software Architecture

• Definition: Software architecture blueprints system structure, components, interactions, and design rationale.
• Components: Subsystems/modules with defined interfaces.
• Connectors: Communication pathways between components (e.g., APIs).
• Configuration: Arrangement of components and connectors.
• Example (Pipes and Filters): Input data broken into tokens (Lexer), tokens into structure (Parser), execution (Evaluator), error handling.

Design Choices and Approaches

• Main-Program-Subroutine Architecture: Hierarchical structure (e.g., Calculator program).
• Object-Oriented Approach: Encapsulates data and methods into classes (e.g., File management system - FileManager,User,Logger).

UML Diagrams

• Unified Modeling Language (UML) diagrams visually represent system components, relationships, and workflows.
• Class Diagram: Describes classes, attributes, methods, and relationships. (Example: Product class with attributes like productID, name, price, methods like getProductDetails(), applyDiscount()).
• Sequence Diagram: Shows object interactions over time. (Example: User logging in).

Multiplicity in UML

• One-to-One: A User has one profile.
• One-to-Many: A Teacher manages many students.
• Many-to-Many: Students enroll in multiple courses, and courses have many students.

Testing

• Types of Testing:
  • Unit Testing: Tests individual modules.
  • Integration Testing: Verifies data flow between modules.
  • System Testing: Tests the complete system against requirements.
• Web Testing:
  • Functional Testing: Tests features (login, search).
  • Compatibility Testing: Ensures website works on different browsers.
  • Performance Testing: Simulates many users.
  • Security Testing: Prevents attacks (SQL Injection, XSS).

Deployment and Maintenance

• Deployment Example (Mobile Banking App): Development, testing, release to App Store, maintenance to fix bugs and enhance features.