Software Design, DFDs & Testing Techniques

This unit explains how the Requirement Model is translated into a Design Model, covering Architectural Design, Interface Design, Component-Level Design, and Data Design with practical examples like turning a login requirement into a User Management module. Key design concepts of Abstraction and Information Hiding are compared in detail, highlighting their differing focus on "what the system does" versus "how it works internally." A major portion covers Data Flow Diagrams (DFDs) — their symbols (Entity, Process, Data Flow, Data Store) and multi-level examples for real systems like a College Management System, Hospital Management System, Book Publishing House, and Railway Reservation System. The notes also introduce Structured Charts, explaining module types (control, sub, library modules) and symbols like condition calls, loops, and data/control flow. Decision Tables are covered as a tabular method for representing complex rules and conditions, with a worked example on customer discounts. The unit closes with comparison tables distinguishing Black Box vs White Box Testing, Static vs Dynamic Testing, and Alpha vs Beta Testing — core testing concepts essential for understanding software verification and validation strategies.