book--domain-driven-design-distilled--nano

OBEY Domain-Driven Design Distilled by Vaughn Vernon

When to use

Use as compact DDD guidance when business language, context ownership, invariants, or integration meaning can affect the code.

Primary bias to correct

DDD is selective modeling for real business complexity, not decorative layers, framework shape, or blanket tactical ceremony.

Decision rules

• Start from business capability, subdomain type, Bounded Context, and local Ubiquitous Language before tactical patterns.
• Invest most design effort in the Core Domain; keep Supporting, Generic, CRUD, and mainly technical areas simpler.
• Put every meaningful model inside one explicit Bounded Context that owns its language, rules, semantics, code, tests, and integration contracts.
• Translate between contexts when meanings differ; never share domain classes or terms whose meanings diverge.
• Choose context relationships and integration mechanisms deliberately, including Conformist or Anticorruption Layer when foreign meaning is involved.
• Keep integration contracts separate from internal models, and do not expose Aggregate internals through REST or transport payloads.
• Use Entities for identity, Value Objects for validated meaning, Aggregates for small invariant boundaries, and Domain Events for meaningful past-tense facts.
• Modify one Aggregate per transaction by default; reference other Aggregates by identity and use eventual consistency when the business allows it.
• Keep business decisions in the domain model; Application Services coordinate use cases.
• Keep frameworks, persistence, transport, and external schemas out of the domain model.
• Use scenarios, acceptance tests, Event Storming, spikes, and domain-expert walkthroughs to learn quickly without hiding modeling debt.

Trigger rules

• When language is fuzzy or overloaded, sharpen terms before coding.
• When one model absorbs unrelated concerns, redraw the subdomain or context boundary.
• When foreign models, schemas, APIs, or frameworks drive domain shape, add boundary translation.
• When a transaction wants many roots or a large graph, revisit Aggregate boundaries and consistency timing.
• When services, controllers, setters, flags, or primitives carry business decisions, expose the missing domain concept.
• When events are vague, command-like, or noisy field changes, redesign them as specific business facts.

Final checklist

• Clear subdomain?
• Clear context?
• Clear language?
• Clear translation?
• Clear invariant boundary?
• Clear modeling debt?