Harmonic Design synthesizes four frameworks into a unified whole. Each retains its full set of rules, role definitions, and validation approach — but HD governs how they connect, how they reinforce each other, and how structural decisions at one layer propagate through all others.
Volatility-Based Decomposition (VBD)
The backend structural model. Organize components around anticipated change, not current functionality.
VBD identifies four volatility axes — functional, orchestration, cross-cutting, and environmental — and assigns each to a dedicated component role. Managers coordinate workflow. Engines execute business rules. Resource Accessors isolate external dependencies. Utilities handle cross-cutting concerns. Communication rules enforce clean boundaries: state flows downward, results propagate upward, horizontal coordination is prohibited.
Experience-Based Decomposition (EBD)
The interface structural model. Structure interfaces around human intent, not screens or components.
EBD establishes three behavioral tiers — Experiences (complete user journeys), Flows (goal-directed sequences), and Interactions (atomic user actions) — plus shared Utilities. The same volatility axes apply: functional change is isolated in Interactions, structural change in Experiences, cross-cutting in Utilities, and environmental in API Accessors. The Experience is the exclusive communicator with the backend.
Boundary-Driven Testing (BDT)
The test strategy map. Testing difficulty is architectural evidence, not a testing problem.
BDT maps the test spiral to the structural models defined by VBD and EBD. Each tier has a natural test profile: Engines and Flows at unit scope, seams between tiers at integration scope, complete journeys at E2E scope. Mock placement follows from structural position — you mock at boundaries because boundaries are the architecturally significant seams.
Project Design (PD)
The project planning model. You cannot estimate what you have not designed.
Project Design derives the project plan from the architectural decomposition. Components become work packages. Dependencies become the project network. The critical path determines duration. Float analysis quantifies risk. The result is not one plan but a set of viable options with quantified trade-offs — enabling rational decision-making rather than guesswork.
How They Connect
The four frameworks are structurally isomorphic. The same volatility axes drive decomposition at every layer. The same communication rules apply. The same validation mechanism — trace a core scenario through the hierarchy — works in all four. A structural insight at one layer informs all layers simultaneously.
| Axis | Backend (VBD) | Interface (EBD) | Testing (BDT) | Planning (PD) |
|---|---|---|---|---|
| Functional | Engine | Interaction | Unit tests | Core Work Package |
| Orchestration | Manager | Experience | Integration tests | Integration Milestone |
| Cross-cutting | Utility | Utility | Unit tests | Shared Infrastructure |
| Environmental | Resource Accessor | API Accessor | Unit (translation) | Boundary Work Package |