Linked Data Export (JSON-LD & RDF)

Katalon has a semantic RDF and JSON-LD serializer that automatically maps collection data to the international ontologies CIDOC-CRM (ISO 21127) and LRMoo (Library Reference Model - object-oriented).

The export is available via the REST API, through content negotiation, via the OAI-PMH interface, and via the built-in SPARQL endpoint (Oxigraph).

Semantic modeling

By default, Katalon’s primary types and relations are mapped to CIDOC-CRM and LRMoo as follows:

Primary types

Katalon type / subtype	RDF classes
`object`	`crm:E22_Human-Made_Object`, `lrmoo:F5_Item`
`occurrence` (subtype `work`)	`lrmoo:F1_Work`
`occurrence` (subtype `expression`)	`lrmoo:F2_Expression`
`occurrence` (subtype `manifestation`)	`lrmoo:F3_Manifestation`
`occurrence` (subtype `event` or other)	`crm:E5_Event`
`entity` (person)	`crm:E21_Person`
`entity` (corporate body / organization)	`crm:E74_Group`
`place`	`crm:E53_Place`

Relations

Relationships between records are automatically translated into matching semantic predicates:

lrmoo:R3_is_realised_in (Work → Expression)
lrmoo:R4_is_embodied_in (Expression → Manifestation)
lrmoo:R7_exemplifies (Item/Object → Manifestation)
crm:P14_carried_out_by (actors / participants)
crm:P138_represents (depicted entities / subjects)
crm:P7_took_place_at (event places)
crm:P67_refers_to (general references)

Incoming relationships are automatically mapped with the corresponding inverse predicates.

Custom RDF properties for relation types

In the Admin UI under Configuration → Vocabularies, on the relation_types system vocabulary, you can set an individual RDF property URI for each relation type. The serializer then prefers this URI on export.

Vocabularies as `skos:Concept`

Classifying fields and vocabularies are not exported as plain text literals only. If a term has a canonical URI or exactMatch references, it is serialized in the JSON-LD as a full skos:Concept node under crm:P2_has_type.

Retrieval via the REST API

Explicit export endpoint

Each primary type has its own export endpoint:

# JSON-LD export for an object
curl "https://katalon.example.org/api/v1/objects/{id}/export?format=jsonld"

# Turtle (TTL) export for a place
curl "https://katalon.example.org/api/v1/places/{id}/export?format=turtle"

Supported formats (?format=):

jsonld or json-ld (MIME type: application/ld+json)
turtle or ttl (MIME type: text/turtle)

Content negotiation

Katalon supports content negotiation directly on the standard record endpoints. Clients can request the desired semantic format via the Accept HTTP header:

# Requests JSON-LD from the standard object endpoint
curl -H "Accept: application/ld+json" \
  "https://katalon.example.org/api/v1/objects/{id}"

# Requests Turtle from the standard entity endpoint
curl -H "Accept: text/turtle" \
  "https://katalon.example.org/api/v1/entities/{id}"

Without a matching RDF Accept header, the endpoint returns the usual application JSON.

Retrieval via OAI-PMH

The semantic export is fully integrated into the OAI-PMH interface.

Via metadataPrefix=json_ld (or short jsonld), harvesters can query collection data in JSON-LD format:

https://katalon.example.org/oai?verb=GetRecord&identifier=oai:katalon:object:{id}&metadataPrefix=json_ld

Or for mass retrieval of entire sets:

https://katalon.example.org/oai?verb=ListRecords&metadataPrefix=json_ld

The format is registered in the OAI-PMH ListMetadataFormats response and references the CIDOC-CRM/LRMoo JSON-LD schema.

SPARQL endpoint

For complex research queries and cross-type graph analysis, the built-in triple store is available:

👉 See SPARQL endpoint (Oxigraph) for documentation of the W3C SPARQL 1.1 interface, authentication, query examples, and named graphs.