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model.md

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+# Abstract Model
+
+## Hierarchy Model
+
+The ABC Pattern defines a strict three‑layer hierarchy of constructs (ABC‑C0):
+
+* Application Stack (ABC‑C1) — the root deployment boundary.
+* Logical Units (ABC‑C2) — first‑level domains within the application.
+* Resource Groups (ABC‑C3) — fine‑grained functional clusters inside each
+  Logical Unit.
+
+This hierarchy is **strictly vertical**.
+
+Every construct belongs to exactly one parent, and no construct may exist
+outside this tree.
+
+The hierarchy expresses **encapsulation**:
+
+* ABC‑C1 encapsulates the entire application.
+* ABC‑C2 encapsulates domain‑level concerns.
+* ABC‑C3 encapsulates resource‑level concerns.
+
+Each layer exposes its behavior exclusively through its Instantiation Interface
+(ABC‑C6) and its Input/Output Contracts (ABC‑C4, ABC‑C5).
+
+## Relationship Semantics
+
+The ABC Pattern enforces a parent–child‑only relationship model.
+
+### Allowed relationships
+
+A parent construct MAY instantiate children using the child’s Instantiation
+Interface (ABC‑C6).
+
+A child MAY expose outputs upward via its Output Contract (ABC‑C5).
+
+A parent MAY route outputs from one child to another via Capturing Down
+(ABC‑C7).
+
+### Forbidden relationships
+
+* **No lateral references:**
+  - Resource Groups (ABC‑C3) may not reference each other directly.
+  - Logical Units (ABC‑C2) may not reference each other directly.
+* **No implicit dependencies:**
+  - A construct may not read global state, shared variables, or parent
+    internals.
+* **No hidden communication channels:**
+  - All data must flow through Input/Output Contracts.
+
+These constraints ensure loose coupling, testability, and predictable
+composition.
+
+## Interface Semantics
+
+Every construct (ABC‑C0) defines two explicit interfaces:
+
+### Input Contract (ABC‑C4)
+
+The complete set of parameters required for instantiation.
+A construct MUST NOT depend on any value not present in its Input Contract.
+
+### Output Contract (ABC‑C5)
+
+The complete set of values the construct exposes upward.
+A construct MUST NOT leak internal state except through this contract.
+
+### Interface Binding
+
+When a parent instantiates a child:
+
+1. The parent supplies the child’s Input Contract.
+2. The child returns its Output Contract.
+3. The parent may:
+
+> * consume the outputs,
+> * aggregate them,
+> * or pass them down to other children.
+
+This creates a **closed, explicit dependency graph** with no hidden edges.
+
+## Instantiation Semantics
+
+The Instantiation Interface (ABC‑C6) is the single mechanism through which a
+construct is created.
+
+It has three properties:
+
+* **Stability** - The interface remains stable even if internal implementation
+  changes.
+* **Minimality** - Only the Input Contract is accepted; no additional
+  parameters.
+* **Purity** - Instantiation has no side effects beyond constructing the child.
+
+Instantiation is always **top‑down**:
+
+* ABC‑C1 instantiates ABC‑C2 constructs.
+* ABC‑C2 instantiates ABC‑C3 constructs.
+* No construct may instantiate its parent or siblings.
+
+This ensures deterministic composition and predictable dependency flow.
+
+## Data Flow Semantics
+
+Data flows vertically through two complementary mechanisms:
+
+### ABC‑F1 — Capturing Down (maps to ABC‑C7)
+
+A parent passes scoped inputs to its children.
+
+This mechanism ensures:
+
+* Children receive only what they need.
+* No child can access parent state implicitly.
+* Parents mediate all cross‑domain dependencies.
+
+### ABC‑F2 — Bubbling Up (maps to ABC‑C8)
+
+A child exposes outputs upward to its parent.
+
+This mechanism ensures:
+
+* All produced values are explicit.
+* Parents can aggregate or route outputs.
+* No child communicates directly with siblings.
+
+### Routing Semantics
+
+Parents MAY:
+
+* **Consume** outputs (e.g., store them).
+* **Transform** outputs (e.g., wrap them in a composite object).
+* **Re‑expose** outputs upward.
+* **Pass** outputs downward to other children.
+
+Children MAY not route data themselves.
+
+## Conceptual Diagram
+
+```default
+Application Stack (ABC‑C1)
+│
+├── Logical Unit: Data (ABC‑C2)
+│     ├── Resource Group: Storage (ABC‑C3)
+│     └── Resource Group: Database (ABC‑C3)
+│
+├── Logical Unit: Logic (ABC‑C2)
+│     ├── Resource Group: Compute (ABC‑C3)
+│     └── Resource Group: Messaging (ABC‑C3)
+│
+└── Logical Unit: Presentation (ABC‑C2)
+      ├── Resource Group: CDN (ABC‑C3)
+      └── Resource Group: WebApp (ABC‑C3)
+```
+
+**Downward arrows** represent Capturing Down (ABC‑F1).
+
+**Upward arrows** represent Bubbling Up (ABC‑F2).
+
+No horizontal arrows exist.
+
+## Rationale & Design Intent
+
+The ABC Pattern enforces a strict, explicit, and testable structure for cloud
+infrastructure code.
+
+* **Encapsulation** ensures each construct hides its internal details.
+* **Explicit interfaces** eliminate hidden dependencies.
+* **Loose coupling** prevents cross‑domain entanglement.
+* **Reusability** emerges from stable Instantiation Interfaces.
+* **Testability** is guaranteed because each construct can be instantiated with
+  mock inputs.
+* **Scalability** follows naturally from the ability to evolve constructs
+  independently.
+
+This model is intentionally tool‑agnostic so it can be mapped cleanly to CDK,
+Terraform, Pulumi, or any imperative, as well as declarative IaC framework.