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The Graph Schema

One node table N, one relationship table E, and one derived-edge table D. The schema is fixed — it does not depend on which constructs an ontology uses.

Node table N

Column Type Meaning
uid STRING (PK) Synthetic id, assigned in document order (n0, n1, …)
kind STRING OWL/XML element name: Class, SubClassOf, ObjectSomeValuesFrom, Literal, …
iri STRING Entity IRI (also Prefix expansion and Datatype IRI); abbreviated IRIs are resolved to full form at parse
node_id STRING AnonymousIndividual blank-node id
datatype_iri STRING Literal datatype
lang STRING Literal language tag
facet STRING FacetRestriction facet IRI
prefix_name STRING Prefix name
ontology_iri, version_iri STRING On the Ontology node
text STRING Element text: Literal value, IRI element content, Import target
cardinality INT64 On cardinality restrictions

Unused columns are null. Named entities of the same kind and identifier are merged: <Class IRI="…#Dog"/> is one node no matter how many axioms mention it, so entity nodes are natural join points. Entities with different OWL kinds may use the same IRI.

Relationship table E

Column Type Meaning
position INT64 Child index in document order — this is what round-trips
role STRING Query-facing name; see Edge Roles

Every edge points from a parent element to a child element. An axiom node's children are its arguments; the Ontology root's children are prefixes, imports, annotations, and axioms.

Derived table D

Column Type Meaning
relation STRING Relation name: subclass_of, type, annotation_value, …
property STRING Property IRI, on relations that carry one (asserts, annotation, …)
quantifier STRING some / only, on restriction edges

D connects the entity (and literal) nodes that a binary axiom relates, collapsing the two-hop walk through the axiom node into one edge. It is a refreshable cache over N/E — graph() and serialization never read it, and derive_edges rebuilds it from current structure. See Derived Relations for the full relation vocabulary.

Reading the shape

A SubClassOf axiom with an annotation looks like:

(:N {kind:'SubClassOf'})
   -[:E {position:0, role:'annotation'}]-> (:N {kind:'Annotation'}) -> …
   -[:E {position:1, role:'sub'}]->        (:N {kind:'Class', iri:'…#Dog'})
   -[:E {position:2, role:'super'}]->      (:N {kind:'Class', iri:'…#Pet'})

Nested expressions nest as deeper trees: a qualified restriction is a node whose filler child is another expression node, and so on. Entity nodes at the leaves are shared across the whole graph.