Tactical Model

Defines what a Tactical Model contains. Does not decide the boundaries — those were fixed at Stage 2; this is the per-Slice detailed design within an already-approved Context, just-in-time (07-stages.md Stage 5).

Schema

schemas/tactical-model.schema.json. A single JSON object per Slice — slices/<id>/tactical-model.json is not an array.

Required fields

slice, aggregates (≥1, each with name, root, invariants).

Content obligations — Vernon's rules, applied (knowledge/ddd-reference.md §2.1)

• Every aggregate declares at least one invariant. An aggregate with no invariant is a data bag, not a domain model — the Stage 5 gate rejects this (trace-lint.py --stage 5). The test: can you state the rule that must hold at the end of every transaction? If not, it isn't an aggregate.
• Reference other aggregates by identity only — never embed one aggregate inside another's structure.
• No invariant should require a synchronous call to a sibling aggregate. This is the specific judgment criterion the Stage 5 architecture-review approval must cover explicitly.
• Domain events are named in the past tense (OrderPlaced, not OrderTableUpdated); commands are named in the imperative (PlaceOrder). A domain expert should recognize the event name.

Behavior-ID citation

Every invariant's behaviors[] must be non-empty — this is both "every aggregate declares ≥1 invariant" and "every design clause cites a Behavior ID" from the Stage 5 gate, in one field. A Behavior assigned to this Slice (per its slice.json.behaviors[]) that is cited by no invariant here is an orphan Behavior in the Slice — also a gate failure.

Unknowns

If an invariant is suspected but its exact statement isn't settled, do not add a placeholder invariant just to satisfy the "≥1 invariant" check — an invariant that doesn't actually hold is worse than an aggregate flagged as needing more design work.

Minimal worked example

{
  "slice": "SLC-0004",
  "aggregates": [
    {
      "name": "Order", "root": "Order",
      "entities": ["OrderLine"], "value_objects": ["Quantity", "Money"],
      "invariants": [
        { "statement": "An Order must contain at least one OrderLine with quantity > 0", "behaviors": ["BHV-0042"] }
      ]
    }
  ],
  "domain_events": [ { "name": "OrderPlaced", "aggregate": "Order" } ],
  "commands": [ { "name": "PlaceOrder", "aggregate": "Order" } ],
  "policies": [ "When OrderPlaced, notify billing-svc" ]
}