A Practical Framework for LLD Domain Modeling in Interviews and System Design

Short summary

A condensed framework for Low-Level Design (LLD) domain modeling, covering the progression from business flow to invariants, entities, state machines, aggregates, bounded contexts, and services. The author argues that strong LLD is about preserving business correctness under constraints, not about syntax or design patterns. The key inversion is starting from behavior and rules rather than jumping to classes.

• •Domain modeling should flow from business flow → invariants → entities → state machines → aggregates → services
• •Interviewers test business correctness thinking, not syntax or UML
• •A good model makes invalid business states hard to create, not complex or deeply abstract

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