# Rule: Slot Nouns Must Be Singular

🚨 **CRITICAL**: LinkML slot names MUST use singular nouns, even for multivalued slots. The `multivalued: true` property indicates cardinality, not the slot name.

## Rationale

1. **Predicate semantics**: Slots represent predicates/relationships. In RDF, `hasCollection` can have multiple objects without changing the predicate name.
2. **Consistency**: Singular names work for both single-valued and multivalued slots.
3. **Ontology alignment**: Standard ontologies use singular predicates (`skos:broader`, `org:hasMember`, `rico:hasOrHadHolder`).
4. **Readability**: `custodian.has_or_had_custodian_type` reads naturally as "custodian has (or had) custodian type".

## Correct Pattern

```yaml
slots:
  has_or_had_custodian_type:        # ✅ CORRECT - singular noun
    slot_uri: org:classification
    range: CustodianType
    multivalued: true               # Cardinality expressed here, not in name

  has_or_had_collection:            # ✅ CORRECT - singular noun
    slot_uri: rico:hasOrHadPart
    range: CustodianCollection
    multivalued: true
    
  has_or_had_member:                # ✅ CORRECT - singular noun
    slot_uri: org:hasMember
    range: Custodian
    multivalued: true
```

## Incorrect Pattern

```yaml
slots:
  has_or_had_custodian_types:       # ❌ WRONG - plural noun
    multivalued: true
    
  collections:                       # ❌ WRONG - plural noun
    multivalued: true
    
  members:                           # ❌ WRONG - plural noun
    multivalued: true
```

## Migration Examples

| Old (Plural) | New (Singular) |
|--------------|----------------|
| `custodian_types` | `has_or_had_custodian_type` |
| `collections` | `has_or_had_collection` |
| `identifiers` | `identifier` |
| `alternative_names` | `alternative_name` |
| `staff_members` | `staff_member` |

## Exceptions

**Compound concepts** where the plural is part of the concept name itself:

- `archives_regionales` - French administrative term (proper noun)
- `united_states` - Geographic proper noun

**NOT exceptions** (still use singular):

- `has_or_had_identifier` not `has_or_had_identifiers` (even if institution has multiple)
- `broader_type` not `broader_types` (even if multiple broader types)

## Implementation

When creating or renaming slots:

1. Extract the noun from the slot name
2. Convert to singular form
3. Combine with relationship prefix (`has_or_had_`, `is_or_was_`, etc.)
4. Set `multivalued: true` if multiple values are expected

## See Also

- `.opencode/rules/slot-naming-convention-current-style.md` - Current slot naming patterns
- `.opencode/rules/slot-centralization-and-semantic-uri-rule.md` - Slot centralization requirements