Invariant

Kind: constraint

Layer: Contracts Core

Record: architecture:invariant

Severity: mandatory

Scope: entity, aggregate, module, system

Canonical: Ontology

A rule or precondition that holds for an entity or aggregate in every state it can reach.

Listed in Architecture principles, after Postconditions and before Backward Compatibility.

Requires

• Encapsulation
• Validation

Reinforces

• Correctness
• Consistency

Enables

• Safe Refactoring

Conflicts with

• External State Mutation

In tension with

• Flexibility

Tensions

• Invariant / Flexibility

Violated by

• Reachable Invalid State

Refactored by

• Encapsulate State
• Factory Pattern
• Validate at the Boundary

Severity

• mandatory

Category

• Contracts / Interfaces / Compatibility

Concept

• Invariant

Enforced by

• rules/eslint/factory-owned-value.eslint.rule.ts
• rules/eslint/validated-construction.eslint.rule.ts

Required by

• Domain Model
• Design by Contract
• Postconditions
• Liskov Substitution Principle

Reinforced by

• Aggregate

Linked from

• Domain Architecture
• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• Core Modular Design
• SOLID / Object-Oriented Design
• Transactions / State / Concurrency
• Contracts / Interfaces / Compatibility
• Core Modular Design
• Core Vocabulary
• Correctness / Determinism / Verification
• Domain Architecture
• SOLID / Object-Oriented Design
• Severity levels
• The resolutions