Querying Your Ontology

Feature Availability

DataHub Core (OSS)

DataHub Cloud

Private BetaInvite-only and evolving rapidly. Contact your DataHub Cloud representative to request access.

Private Beta

Ontology is currently in Private Beta. Features, UI, and configuration options are subject to change.

This page covers reading the relationship graph from code, and from an AI agent.

All the surfaces here run the same multi-hop relationship walk: start at an entity, follow a named set of relationship types, up to a maximum number of hops, and return everything reached.

Available in DataHub Cloud v2.2.1 and later; no feature flag is required.

Discovering what you can traverse

There is no "all relationship types" wildcard — you name the types you want to walk. To find out which types exist on your instance, export the relationship-graph schema. It returns every relationship type with the entity types it connects, its direction semantics, and whether it is built in (NATIVE) or user-defined (CUSTOM):

curl -H "Authorization: Bearer $DATAHUB_TOKEN" \
  "$DATAHUB_GMS_URL/openapi/v3/relationship/schema?entityType=glossaryTerm"

PREFIX dh:     <urn:li:ontology:>
PREFIX et:     <urn:li:entityType:datahub.>
PREFIX rel:    <urn:li:relationshipType:>
PREFIX schema: <https://schema.org/>

rel:governedBy  rdf:type       rdf:Property ;
        rdfs:label             "Governed By" ;
        rdfs:comment           "The regulation or policy term that governs this concept." ;
        schema:domainIncludes  et:glossaryTerm ;
        schema:rangeIncludes   et:glossaryTerm ;
        dh:origin              "CUSTOM" ;
        dh:reverseDisplayName  "Governs" .

The subjects it returns are exactly the values you pass as relationship types below. Add ?format=json-ld (or n-triples, rdf-xml) if Turtle is not what you want.

Traversing from the REST API

GET /openapi/v3/relationship/traverse walks the graph and returns the entities it reached:

curl -H "Authorization: Bearer $DATAHUB_TOKEN" \
  "$DATAHUB_GMS_URL/openapi/v3/relationship/traverse\
?urn=urn:li:glossaryTerm:customer\
&relationshipTypes=IsA\
&relationshipTypes=urn:li:relationshipType:governedBy\
&direction=UNDIRECTED\
&maxHops=2"

{
  "count": 2,
  "total": 2,
  "partial": false,
  "relationships": [
    {
      "relationshipType": "urn:li:relationshipType:governedBy",
      "entityType": "glossaryTerm",
      "urn": "urn:li:glossaryTerm:gdpr",
      "degree": 1,
      "degrees": [1],
      "directionMode": "DIRECTED",
      "transitive": false,
      "reverseDisplayName": "Governs"
    },
    {
      "relationshipType": "IsA",
      "entityType": "glossaryTerm",
      "urn": "urn:li:glossaryTerm:businessCustomer",
      "degree": 1,
      "degrees": [1],
      "directionMode": "DIRECTED",
      "transitive": false
    }
  ]
}

Parameters

Parameter	Meaning
urn	The entity to start from. Required.
relationshipTypes	Repeatable. Built-in names (IsA, HasA, DownstreamOf, …) and/or urn:li:relationshipType:* URNs, traversed uniformly. A urn:li:structuredProperty:* URN is accepted too and resolves to the relationship type it points at. Required unless includeLineage=true.
direction	OUTGOING (default), INCOMING, or UNDIRECTED. Edges point from the entity holding the metadata to the entity it references, so INCOMING from X returns entities whose edges point at X. Symmetric relationship types are walked both ways regardless.
maxHops	Traversal depth, 1–20. Defaults to 1.
entityTypes	Repeatable. Constrains the entity types visited at every hop, not just the final results.
includeLineage	Also walk the full native lineage edge set in the same call, without enumerating lineage relationship types.
lineageDirection	UPSTREAM, DOWNSTREAM, or BOTH (default). Only meaningful with includeLineage=true.
resolveEquivalents	Expand a requested standard-vocabulary predicate (e.g. skos:broader) to the relationship types that declare it as an equivalent.

degree is the hop distance from the start entity; degrees lists every depth at which the entity was reached. partial: true means the walk hit a traversal limit or timed out — narrow the query.

Traversing from GraphQL

The searchAcrossRelationships query is the same walk with hydrated entities, plus paging. This is what the ontology graph UI itself calls:

query {
  searchAcrossRelationships(
    input: {
      urn: "urn:li:glossaryTerm:customer"
      relationshipTypes: ["IsA", "HasA", "urn:li:relationshipType:governedBy"]
      direction: UNDIRECTED
      maxHops: 2
      count: 50
    }
  ) {
    total
    isPartial
    relationships {
      relationshipType
      degree
      directionMode
      transitive
      reverseDisplayName
      entity {
        urn
        ... on GlossaryTerm {
          properties {
            name
            description
          }
        }
      }
    }
  }
}

Page with start and count. isPartial carries the same meaning as partial above.

Lineage is a separate axis

relationshipTypes and direction apply only to the named-relationship walk. When includeLineage is true, the full native lineage edge set is traversed as well — controlled solely by lineageDirection — and the two walks are unioned. For pure data-flow questions ("what feeds this table?"), use the lineage APIs instead; they are built for it.

Querying from an AI agent

DataHub's MCP server exposes the same walk as the get_relationships tool, so an assistant can answer ontology questions directly. Paired with get_metadata_graph — the MCP equivalent of the schema export above — an agent can discover what relationship types exist and then traverse them, without any of them being hardcoded.

A useful pattern to give an agent:

Call get_metadata_graph first to see which relationship types connect which entity types on this instance, then call get_relationships with the ones relevant to the question.

get_relationships mirrors the REST parameters (urn, relationship_types, direction, max_hops, entity_types, include_lineage, lineage_direction), and adds a fields allowlist so the agent only pulls the entity fields it needs — keeping more results inside its token budget. Results are paged: pass the response's nextOffset back as offset and stop when hasMore is false.

See DataHub MCP Server for connecting an agent to your instance.

Practical notes

• Name your types. There is no wildcard. A walk over the wrong types returns nothing, and it looks identical to a walk over an entity with no relationships.
• Be careful with entityTypes on multi-hop walks. The filter applies at every hop, so a path that passes through an excluded entity type is cut short. Prefer omitting it when maxHops > 1.
• Watch for isPartial / partial. A capped walk is not an empty one. Narrow the relationship types or entity types, or reduce the hop count, rather than trusting a truncated answer.
• Authorization applies. A walk only returns entities the caller is allowed to view.

If you need to express the query itself in a standard graph query language rather than as walk parameters, see Advanced Querying with SPARQL.