# Exact Mapping Predicate/Class Distinction Rule

🚨 **CRITICAL**: The `exact_mappings` property implies semantic equivalence. Equivalence can only exist between elements of the same ontological category.

## The Rule

1.  **Slots (Predicates)** MUST ONLY have `exact_mappings` to ontology **predicates** (properties).
    *   ❌ INVALID: Slot `analyze` maps to `schema:object` (a Class).
    *   ✅ VALID: Slot `analyze` maps to `crm:P129_is_about` (a Property).

2.  **Classes (Entities)** MUST ONLY have `exact_mappings` to ontology **classes** (entities).
    *   ❌ INVALID: Class `Person` maps to `foaf:name` (a Property).
    *   ✅ VALID: Class `Person` maps to `foaf:Person` (a Class).

3.  **When true equivalence exists and is verified, exact mapping is preferred.**
    *   ✅ VALID: Class `Acquisition` maps to `crm:E8_Acquisition`.
    *   ✅ VALID: Slot mapped to an actually equivalent ontology property.
    *   ❗ Do not avoid `exact_mappings` by default; avoid only when scope is broader/narrower/similar-but-not-equal.

## Rationale

Mapping a slot (which defines a relationship or attribute) to a class (which defines a type of entity) is a category error. `schema:object` represents the *class* of objects, not the *relationship* of "having an object" or "analyzing an object".

## Verification Checklist

When adding or reviewing `exact_mappings`:
- [ ] Is the LinkML element a Class or a Slot?
- [ ] Did you verify the target term type in the ontology definition files (do not rely on naming heuristics)?
- [ ] Do they match? (Class↔Class, Slot↔Property)
- [ ] If the target ontology uses opaque IDs (like CIDOC-CRM `E55_Type`), verify the type definition in the ontology file.
- [ ] If semantic scope is truly equivalent, use `exact_mappings` (not `close`/`broad` as a conservative fallback).

## Common Pitfalls to Fix

- Mapping slots to `schema:Object` or `schema:Thing`.
- Mapping slots to `skos:Concept`.
- Mapping classes to `schema:name` or `dc:title`.