# CustodianAppellation Relationship Refactoring - Phase 2

**Date**: 2025-11-22  
**Session**: OpenCode AI Agent (Phase 2)  
**Status**: ✅ COMPLETE

---

## Executive Summary

Refactored the Heritage Custodian Ontology to correctly model the relationship between `CustodianAppellation` and `CustodianName`, aligning with W3C SKOS best practices and ensuring `CustodianIdentifier` is the only class that directly identifies the `Custodian` hub.

**This is Phase 2** of the Appellation/Identifier refactoring:
- **Phase 1** (Nov 22, morning): Connected orphaned classes to Custodian hub ✅
- **Phase 2** (Nov 22, afternoon): Moved appellations from Custodian to CustodianName ✅

---

## Problem Statement

### Phase 1 Architecture (Correct but Improvable)

After Phase 1 refactoring:
```
Custodian --[crm:P1_is_identified_by]--> CustodianAppellation
Custodian --[crm:P48_has_preferred_identifier]--> CustodianIdentifier
```

**Issues Discovered**:
1. **Semantic confusion**: `crm:P1_is_identified_by` suggests appellations *identify* the Custodian hub
2. **Inconsistent hub design**: Both Identifier and Appellation claimed to identify the hub
3. **Missing name aspect**: Appellations should be variants of the canonical name, not hub identifiers
4. **Ontology misalignment**: W3C Org Ontology uses `skos:altLabel` for alternative names, not `crm:P1`

---

## Solution

### Phase 2 Architecture (Correct and Aligned with SKOS)

```
Custodian (hub)
  └─ skos:prefLabel ──> CustodianName (canonical emic name)
       └─ skos:altLabel ──> CustodianAppellation (name variants)

Custodian (hub)
  └─ crm:P48_has_preferred_identifier ──> CustodianIdentifier (external IDs)
```

**Key Changes from Phase 1**:
1. **CustodianAppellation connects to CustodianName** (not Custodian)
2. **Uses `skos:altLabel`** (standard property for alternative lexical labels)
3. **Only CustodianIdentifier identifies the hub** (maintains clean hub architecture)
4. **Inverse relationship**: `CustodianAppellation.variant_of_name` → `CustodianName` (using `skos:broader`)

---

## Files Modified

### 1. Schema Module Files

#### `/schemas/20251121/linkml/modules/classes/Appellation.yaml` ✅
**Changes**:
- Updated description: "alternative name variants for CustodianName" (was "custodian")
- Changed slot from `identifies_custodian` → `variant_of_name`
- Changed slot_uri from `crm:P1i_identifies` → `skos:broader`
- Range changed from `Custodian` → `CustodianName`
- Added import for `CustodianName` class
- Updated documentation with SKOS altLabel rationale

#### `/schemas/20251121/linkml/modules/classes/Custodian.yaml` ✅
**Changes**:
- **Removed** `appellations` slot from slots list (line 99)
- **Removed** `appellations` slot_usage block (lines 169-178)
- Updated documentation: "Alternative names (in CustodianName.alternative_names list)"

#### `/schemas/20251121/linkml/modules/classes/CustodianName.yaml` ✅
**Changes**:
- **Added** `alternative_names` slot to slots list
- **Added** `alternative_names` slot_usage:
  - `slot_uri: skos:altLabel`
  - `range: CustodianAppellation`
  - `multivalued: true`
  - Examples: "BnF", "Rijks", translations, historical variants
- Added related mappings: `foaf:nick`, `gleif:hasOtherName`

### 2. New Slot Files Created

#### `/schemas/20251121/linkml/modules/slots/alternative_names.yaml` ✅
**Purpose**: CustodianName → CustodianAppellation relationship
- `slot_uri: skos:altLabel`
- `range: CustodianAppellation`
- `multivalued: true`
- Domain: CustodianName (SKOS Concept)

#### `/schemas/20251121/linkml/modules/slots/variant_of_name.yaml` ✅
**Purpose**: CustodianAppellation → CustodianName inverse relationship
- `slot_uri: skos:broader`
- `range: CustodianName`
- Domain: E41_Appellation
- Inverse of `skos:altLabel`

### 3. Main Schema File

#### `/schemas/20251121/linkml/01_custodian_name_modular.yaml` ✅
**Changes**:
- **Removed import**: `modules/slots/appellations`
- **Added imports**: 
  - `modules/slots/alternative_names`
  - `modules/slots/variant_of_name`
- Updated change log:
  - "New slots (3): alternative_names (CustodianName → CustodianAppellation), variant_of_name (inverse), identifies_custodian (Identifier → Custodian)"
  - "Architecture change: CustodianAppellation now connects to CustodianName (not Custodian) using skos:altLabel"

### 4. Deprecated Files

#### `/schemas/20251121/linkml/modules/slots/appellations.yaml` ⚠️ DEPRECATED
**Status**: Marked as deprecated with clear migration path
- Added deprecation notice explaining why it was replaced
- Documents old architecture vs. new architecture
- Points to replacement files (`alternative_names.yaml`, `variant_of_name.yaml`)
- Kept for historical reference only

---

## Ontology Alignment

### SKOS (Simple Knowledge Organization System)

**Primary Property**: `skos:altLabel`
- **Definition**: "An alternative lexical label for a resource"
- **Use case**: "Trading names, colloquial names, abbreviations, acronyms"
- **Source**: W3C Org Ontology (org:alternativeName → skos:altLabel)

**Inverse Property**: `skos:broader`
- Links alternative label back to its preferred concept
- Standard SKOS hierarchical relationship

### Related Ontology Properties

- **W3C Org Ontology**: `org:alternativeName` (subproperty of `skos:altLabel`)
- **GLEIF**: `gleif:hasOtherName` (subproperty of `skos:altLabel`)
- **FOAF**: `foaf:nick` (for nicknames)
- **Schema.org**: `schema:alternateName` (close match)

---

## Generated Outputs

### RDF Formats (Timestamp: `20251122_181217` - `20251122_181224`)

```bash
schemas/20251121/rdf/
├── 01_custodian_name_modular_20251122_181217.owl.ttl  (160 KB - OWL/Turtle)
├── 01_custodian_name_modular_20251122_181224.nt       (458 KB - N-Triples)
├── 01_custodian_name_modular_20251122_181224.jsonld   (382 KB - JSON-LD)
└── 01_custodian_name_modular_20251122_181224.rdf      (330 KB - RDF/XML)
```

**Validation**: ✅ All files generated successfully with `gen-owl` and `rdfpipe`

### UML Diagrams (Timestamp: `20251122_181237`)

```bash
schemas/20251121/uml/mermaid/
└── 01_custodian_name_modular_20251122_181237_er.mmd  (176 lines - ER diagram)
```

**Key Relationships Verified**:
```mermaid
CustodianName ||--}o CustodianAppellation : "alternative_names"
CustodianAppellation ||--|o CustodianName : "variant_of_name"
```

---

## Architecture Evolution

### Phase 1 → Phase 2 Comparison

| Aspect | Phase 1 | Phase 2 |
|--------|---------|---------|
| **Appellation connects to** | Custodian (hub) | CustodianName (aspect) |
| **Property used** | `crm:P1_is_identified_by` | `skos:altLabel` |
| **Inverse property** | `crm:P1i_identifies` | `skos:broader` |
| **Semantic meaning** | "Appellation identifies hub" | "Appellation is variant of name" |
| **Ontology alignment** | CIDOC-CRM | W3C SKOS + CIDOC-CRM |
| **Slot name** | `appellations` | `alternative_names` |

---

## Examples

### Phase 1 (Before Phase 2)

```yaml
# Phase 1 architecture - Connected but semantically confused
Custodian:
  id: https://nde.nl/ontology/hc/cust/bnf
  appellations:  # ⚠️ Direct connection to hub (problematic)
    - appellation_value: "BnF"
      appellation_type: ABBREVIATION
      identifies_custodian: https://nde.nl/ontology/hc/cust/bnf  # Suggests it identifies hub
```

### Phase 2 (After Phase 2)

```yaml
# Phase 2 architecture - CORRECT!
Custodian:
  id: https://nde.nl/ontology/hc/cust/bnf
  preferred_label:
    refers_to_custodian: https://nde.nl/ontology/hc/cust/bnf
    emic_name: "Bibliothèque nationale de France"
    alternative_names:  # ✅ Connection through CustodianName
      - appellation_value: "BnF"
        appellation_type: ABBREVIATION
        variant_of_name: <link back to CustodianName>
      - appellation_value: "National Library of France"
        appellation_language: "en"
        appellation_type: TRANSLATION
```

---

## RDF Serialization

### Turtle (TTL) - Phase 2

```turtle
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix crm: <http://www.cidoc-crm.org/cidoc-crm/> .

<https://nde.nl/ontology/hc/cust/bnf> 
    skos:prefLabel <https://nde.nl/ontology/hc/name/bnf-001> .

<https://nde.nl/ontology/hc/name/bnf-001>
    a crm:E33_Linguistic_Object ;
    rdf:value "Bibliothèque nationale de France" ;
    skos:altLabel <https://nde.nl/ontology/hc/appellation/bnf-abbrev> .

<https://nde.nl/ontology/hc/appellation/bnf-abbrev>
    a crm:E41_Appellation ;
    rdf:value "BnF" ;
    skos:broader <https://nde.nl/ontology/hc/name/bnf-001> .
```

---

## Validation Results

### LinkML Schema Validation ✅

```bash
$ gen-owl -f ttl 01_custodian_name_modular.yaml
# Output: 160 KB OWL/Turtle file with no errors
```

**Warnings** (non-critical):
- ⚠️ Multiple owl types for `language` (rdfs:Literal vs owl:Thing) - expected for ambiguous ranges
- ⚠️ Schema namespace override (schema.org vs schema:) - cosmetic, doesn't affect semantics

### ER Diagram Validation ✅

**Relationships Confirmed**:
1. ✅ `Custodian ||--|o CustodianName : "preferred_label"` (hub → name)
2. ✅ `CustodianName ||--}o CustodianAppellation : "alternative_names"` (name → variants, one-to-many)
3. ✅ `CustodianAppellation ||--|o CustodianName : "variant_of_name"` (variant → name, inverse)
4. ✅ `Custodian ||--}o CustodianIdentifier : "identifiers"` (hub → external IDs)
5. ✅ `CustodianIdentifier ||--|o Custodian : "identifies_custodian"` (ID → hub, identifies)

**Key Observation**: ❌ No direct Custodian ↔ Appellation relationship exists (by design!)

---

## Impact Analysis

### Benefits

1. **Semantic clarity**: Appellations are now clearly name variants, not hub identifiers
2. **Ontology alignment**: Uses standard `skos:altLabel` (W3C recommended practice)
3. **Clean hub architecture**: Only `CustodianIdentifier` identifies the hub
4. **Multi-aspect modeling**: Names can have independent alternative labels
5. **Bidirectional relationships**: Both forward (`alternative_names`) and inverse (`variant_of_name`)

### Breaking Changes from Phase 1

⚠️ **Data Migration Required**:

**Phase 1 data structure**:
```yaml
Custodian:
  appellations: [list of CustodianAppellation]
```

**Phase 2 data structure**:
```yaml
Custodian:
  preferred_label:  # CustodianName
    alternative_names: [list of CustodianAppellation]
```

**Migration Script**: TODO - Create conversion script for existing data

---

## Design Rationale

### Why `skos:altLabel` Instead of `crm:P1_is_identified_by`?

**CIDOC-CRM `crm:P1_is_identified_by`**:
- ✅ Purpose: "Names and labels used to **identify** this custodian"
- ❌ Problem: Suggests appellations identify the **hub entity**
- ❌ Conflicts with: `CustodianIdentifier` being the only hub identifier

**SKOS `skos:altLabel`**:
- ✅ Purpose: "Alternative lexical label for a resource"
- ✅ Standard for: Trading names, colloquial names, abbreviations
- ✅ Aligns with: W3C Org Ontology best practices
- ✅ Clear semantics: Alternative labels for a **name aspect**, not hub identifiers

### Why CustodianName, Not Custodian?

**Aspect-Based Architecture**:
- `CustodianName` = One aspect of the custodian (the emic designation)
- `CustodianIdentifier` = Different aspect (external identifiers)
- `CustodianLegalStatus` = Different aspect (legal entity)

**Each aspect has independent lifecycle**:
- Names can have alternative variants (appellations)
- Identifiers can reference external systems (ISIL, Wikidata)
- Legal statuses can have registration numbers (KvK, company ID)

**Mixing aspects breaks the model**:
- ❌ Custodian.appellations → Implies hub has name variants (wrong level of abstraction)
- ✅ CustodianName.alternative_names → Correct level (names have variants)

---

## Testing Checklist

- [x] LinkML schema validation passes
- [x] OWL/Turtle generation succeeds
- [x] RDF format conversions (N-Triples, JSON-LD, RDF/XML)
- [x] Mermaid ER diagram generation
- [x] Relationships verified in ER diagram
- [x] Deprecated file marked with migration path
- [x] Main schema imports updated
- [ ] Unit tests for data instances (TODO)
- [ ] Migration script for existing data (TODO)

---

## Related Documentation

### Files to Update

1. **README.md** - Update architecture diagrams showing new relationships
2. **SCHEMA_MODULES.md** - Document `alternative_names` and `variant_of_name` slots
3. **ONTOLOGY_EXTENSIONS.md** - Add section on SKOS altLabel usage
4. **Data migration guide** - Create step-by-step conversion instructions

### Reference Documents

- **W3C Org Ontology**: https://www.w3.org/TR/vocab-org/#org:alternativeName
- **SKOS Reference**: https://www.w3.org/TR/skos-reference/#altLabel
- **CIDOC-CRM E41_Appellation**: http://www.cidoc-crm.org/Entity/e41-appellation/version-7.1.1
- **GLEIF Ontology**: https://www.gleif.org/ontology/Base/hasOtherName

---

## Phase Comparison Summary

| Phase | Date | Focus | Status |
|-------|------|-------|--------|
| **Phase 1** | 2025-11-22 AM | Connect orphaned Appellation/Identifier to Custodian hub | ✅ Complete |
| **Phase 2** | 2025-11-22 PM | Move Appellation from Custodian to CustodianName (SKOS alignment) | ✅ Complete |

**See Also**:
- `APPELLATION_IDENTIFIER_REFACTORING_20251122.md` - Phase 1 documentation
- `LEGAL_ENTITY_REFACTORING.md` - Legal entity model (context for Phase 1)

---

## Next Steps

### Immediate (Required Before v0.2.0 Release)

1. **Create data migration script** (`scripts/migrate_appellations_phase2_20251122.py`)
   - Convert Phase 1 `Custodian.appellations` to Phase 2 `CustodianName.alternative_names`
   - Validate all existing YAML instance files
   - Generate migration report

2. **Update documentation**:
   - README.md architecture diagrams
   - SCHEMA_MODULES.md slot documentation
   - Examples in LinkML schema comments

3. **Add unit tests**:
   - Test CustodianName with alternative_names
   - Test CustodianAppellation.variant_of_name inverse
   - Validate SKOS altLabel RDF serialization

### Future Enhancements

1. **Add language-tagged appellations**:
   - Support multilingual variants with proper `@lang` tags
   - RDF example: `skos:altLabel "BnF"@fr, "National Library of France"@en`

2. **Appellation provenance**:
   - Track source of alternative names
   - Add temporal validity (when name was used)

3. **Authority control integration**:
   - Link appellations to name authority records (VIAF, ISNI)
   - Validate variant forms against authority files

---

## Conclusion

Phase 2 successfully aligns the Heritage Custodian Ontology with W3C SKOS best practices, maintains clean hub architecture, and provides clear semantic distinction between:

- **CustodianIdentifier**: External identifiers that reference the hub
- **CustodianAppellation**: Alternative name variants for the canonical emic name

This change improves ontology interoperability, semantic clarity, and prepares the schema for future extensions (multilingual support, authority control, provenance tracking).

---

**Version**: v0.1.0 → v0.2.0 (Phase 2)  
**Schema Status**: ✅ Validated  
**RDF Generation**: ✅ Complete (4 formats)  
**Diagrams**: ✅ Generated (Mermaid ER)  
**Data Migration**: ⏳ Pending (Phase 2 → Phase 1 conversion script needed)

---

*End of Phase 2 Report*