layers-conceptual-model

What this skill does

# /layers-conceptual-model

*Assumes `/layers-intro` has been loaded. This skill is a library of techniques, not a script — see "How to use these skills" there.*

The conceptual model is the most neglected load-bearing layer. It defines the objects the product recognises, how they relate, what states they can be in, and the vocabulary for all of it — a deliberate decision about how the product models its domain, independent of any interface.

It is **not** the users' messy mental model (that's the domain layer), and **not** a database schema, wireframe, or flow. But the gap between this model and what engineers build matters: a large, unexamined gap is both UX debt (users meet a product that contradicts the model) and technical debt (the system is hard to evolve).

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## The decisions this layer makes

- What objects the product recognises, and where each object's boundary is
- How those objects relate — cardinality, and named roles where an object plays several
- What a user can do to or with each object
- What states an object can be in, and which transitions matter
- The product's vocabulary — one name per concept, one concept per name

If none of these is genuinely open, you may not need this layer right now. Say so rather than working it for the sake of it.

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## Disciplines — what keeps the model honest

Apply these to whatever you produce, in any order. They are the high-value part of this layer.

- **Real objects only.** A true object is *instanceable* (you can have many), *structured* (has its own attributes), and *useful* (the user cares about it in its own right). This catches two errors: an attribute promoted to an object, and — more often — **instances mistaken for objects**: "CAC" and "ROAS" aren't objects, they're instances of one object, **Metric**. When several nouns are of-a-kind, model the type as the object; the specific names are instances or values.
- **Attributes that are really relationships.** If an attribute is just the name or ID of another object in the model, model it as a relationship — don't duplicate it.
- **Name the role when an object plays several.** "belongs to one User (as referrer)", not "belongs to one User."
- **No speculative additions.** Every object, attribute, action, and relationship should trace to a stated user need. Scope creep here propagates through every layer above. (Tracing to *strategy vocabulary* doesn't count — strategy words aren't yet objects.)
- **Can-be-an-object ≠ should-be-first-class.** The "real objects only" test tells you something *can* be an object — not that the product should commit to it as a first-class, persistent, stateful entity. That elevation is a design bet with a cost. Justify it by concrete use: *what flow or job forces this thing to persist, hold state, and be returned to?* If nothing does, it's transient, or it's premature. And when an object exists only because of an unvalidated strategy bet, mark it **provisional** — model it as a hypothesis, don't "lock" it, and don't build the layer above on it until the bet is tested.
- **Verb precision.** Does a generic verb (Edit, Delete, Update) hide operations with different real-world consequences? "Edit address" conflates correcting a typo (overwrite is fine) with recording a house move (which should preserve history). When a generic verb could mean genuinely different things, name the operations separately — "Correct address" vs "Register change of address" isn't verbose, it's precise.
- **Implementation is not design.** When talk drifts to how something is stored, generated, or computed, redirect to what the user can do and what happens to things that referenced it. Flag genuinely entangled questions for an engineering conversation rather than forcing a premature answer.

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## Techniques

Pick the one that fits the live decision — don't run them all.

| Technique | Use it to |
|---|---|
| **Noun foraging + OOUX** (Sophia Prater) | Extract objects from research or domain notes. The default when you have naturalistic language to mine. Sort nouns into objects / attributes / instances-or-values / set-aside (UI elements, vague abstractions, actions dressed as nouns), using the "real objects only" test above. |
| **Object definition** | Pin down one object: what it is (one sentence, the user's view), its attributes, its relationships (cardinality + role names), and its actions. |
| **Sketch the flow first** (push forward, pull back) | Objecthood is uncertain — whether something should be a persistent object depends on how it's used. Breadboard the flow (`/layers-interaction-flow`) to see what must persist, hold state, or be returned to, then come back and formalise only those. Often the fastest way to tell a real object from a transient one. |
| **Relational object map** (`erDiagram`) | See objects and relationships together and catch missing, reversed, or spurious connections. `\|\|`=exactly one, `o{`=zero-or-many, `\|{`=one-or-many; crow's foot on the many side; labels read first entity → second. |
| **State transition diagram** (`stateDiagram-v2`) | For an object whose status changes what users can do — name the states, the transitions, and what each state forbids. |
| **Action (CTA) inventory** | List every action a user can take, across all objects, in one place — the product's call-to-action vocabulary. Listing them together (not object by object) is what exposes inconsistency (Add vs Create vs New for one operation) and over-flattening (one verb hiding distinct operations). |
| **Ubiquitous language list** | Resolve naming. For each contested concept: the chosen term, rejected alternatives, and why. One name per concept, one concept per name — in UI, help text, API names, and internal talk alike. |
| **Semantic IxD / action grammar** (Rosenberg) | Audit verb consistency and precision across many actions and objects. |
| **Event storming — commands/policies** (Brandolini) | Process-heavy domain: start from what happens, work back to the objects involved. |
| **Card sorting** | Vocabulary is unclear or contested across users or teams. |
| **Walking the existing product** | Redesign: the current UI reveals the implicit model — compare it to how users actually think. |

Also probe the **temporal decisions** from `/layers-intro` — intermediate action states, read-model lag, relationship temporality, deletion semantics, history — for any object where they bite.

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## Working with the designer

Find which of the decisions above are live. Offer the technique that fits: noun foraging if there's material to mine, walking the product if redesigning, or straight to object definition if the objects are known and only their shape is open. Do the next useful thing, not the whole toolkit.

Capture only the residue — the object definitions that got settled (and which are still **provisional**, pending a bet or a flow), any diagram that encodes a real relationship or lifecycle, the vocabulary calls, and the open questions (objects that felt thin, decisions deferred to engineering). Don't write a report the designer won't reread.

If domain work hasn't been done, say plainly: this model is a hypothesis until there's evidence.

When the objects and actions are stable, the natural next move is to design how users move through them — `/layers-interaction-flow`.