Layered System Architecture

Principle 02 · LSA

Layered System Architecture

AI Agents working on complex long-horizon projects need a stable source of truth. They operate by reading Specifications, code, and Designs, then proposing or making changes. When essential purpose and critical Constraints are entangled with volatile implementation details, AI Agents must continually re-infer what must remain true. This increases inconsistency and error.

Stable, high-value parts of the System must not depend on volatile implementation details.

The essential purpose, Invariants (conditions or properties that must always remain true for the System, regardless of its state), and critical behaviors are treated as high-stability elements. These define what the System is and what it must guarantee.

The particular ways those guarantees are achieved (choice of technologies, materials, vendors, control systems, construction methods, interfaces, delivery mechanisms, configuration values, operating parameters, etc.) are treated as lower-stability elements.

Configuration values and parameters that belong to lower-stability elements should be kept explicit and external rather than buried inside high-stability design or logic.

Dependencies must flow from lower-stability elements toward higher-stability elements. High-stability elements must never depend on lower-stability elements.

Consequences:

  • AI Agents and humans can reason about, verify, and evolve the essential purpose and Invariants without being entangled in particular implementation choices.
  • Changes to materials, vendors, software frameworks, sensors, or construction techniques do not force redesign of what the System must guarantee.
  • The Blast Radius of AI Agent actions is limited: AI Agents may freely modify lower-stability elements without silently breaking the high-stability core.
  • High-stability elements can carry strong, relatively unchanging Acceptance Criteria that AI Agents or verification processes can check independently of current Realization details.
  • Multiple AI Agents can work on different lower-stability parts in parallel while sharing a common, stable Contract.
  • Over long-horizon projects, the core remains authoritative even as implementation technologies and methods are replaced repeatedly.

This principle applies equally to software Systems and to physical Systems like floating cities.

In software, high-stability elements include core domain rules, business Invariants, and critical System behaviors. Lower-stability elements include particular databases, web frameworks, UI libraries, cloud providers, or third-party services.

In a floating city, high-stability elements include structural integrity under marine conditions, life-support balance, safety Invariants, and long-term habitability. Lower-stability elements include specific hull materials, power-generation hardware, sensor models, or construction sequences.

Applied in the Specification #

These clauses of the Normative Structural Specification name Layered System Architecture among their grounds.