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UML Deep Dive: Class Diagrams and Sequence Diagrams Who this is for: Anyone who has been designing classes and systems (perhaps through OOP, SOLID, and design patterns) and now wants a standardized visual language to communicate those designs to teammates, interviewers, and their own future self. Table of Contents Why UML Exists The 14 UML Diagram Types: A Complete Map Class Diagrams: Anatomy of a Class Box Abstract Classes vs. Interfaces: Are They the Same Thing? Class Diagrams: Relationships Between Classes Class Diagrams: Advanced Concepts Sequence Diagrams: Why We Need a Second Diagram Sequence Diagrams: Anatomy and Core Concepts Sequence Diagrams: Control Flow (alt, opt, loop, par) 9.5 More Sequence Diagram Examples Putting It All Together: A Simple E-Commerce System 10.1 The Complete Class Diagram 10.2 The Complete Sequence Diagram Summary and Key Takeaways Practice Questions with Solutions 1. Why UML Exists When a design exists only in someone’s head, or scattered across a codebase, it is expensive to communicate. Explaining a system in prose forces the listener to reconstruct a graph of classes and relationships from a linear sequence of sentences, and details get lost or misinterpreted along the way. Two people reading the same paragraph of design prose regularly walk away with two different mental models of the same system, particularly around exactly how strong a relationship between two entities is. ...