Worked example — subclass chain

A two-hop rdfs:subClassOf example you can copy-paste into psql and watch run end-to-end.

Setup

sql

SELECT pgrdf.add_graph(100);

SELECT pgrdf.parse_turtle('
@prefix ex:   <http://example.com/> .
@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

ex:Engineer rdfs:subClassOf ex:Person .
ex:Person   rdfs:subClassOf ex:Agent .
ex:alice    rdf:type        ex:Engineer .
', 100);
--  → 3

We've stated three things explicitly. Without materialization, a query asking "what types does Alice have?" returns only the one that was asserted directly:

sql

SELECT * FROM pgrdf.sparql(
  'PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
   PREFIX ex:   <http://example.com/>
   SELECT ?c WHERE { ex:alice rdf:type ?c }');
--  → {"c": "http://example.com/Engineer"}

Materialize

sql

SELECT pgrdf.materialize(100);

json

{
  "base_triples":              3,
  "inferred_triples_written":  11,
  "total_after":               14,
  "elapsed_ms":                12.3
}

The reasoner emits 11 new triples. (The exact count varies with the OWL 2 RL closure — it includes RDFS-style class declarations like ex:Person rdf:type rdfs:Class, plus the transitive type assertions.)

Query again

sql

SELECT * FROM pgrdf.sparql(
  'PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
   PREFIX ex:   <http://example.com/>
   SELECT ?c WHERE { ex:alice rdf:type ?c }');
--  → {"c": "http://example.com/Engineer"}   ← base
--  → {"c": "http://example.com/Person"}     ← inferred
--  → {"c": "http://example.com/Agent"}      ← inferred

The transitive subclass chain is now queryable as flat rows. Your application can ask "is Alice an Agent?" and get yes, without implementing the closure itself.

Inspect the breakdown

sql

-- See which rows are inferred vs. base.
SELECT
    d_p.value AS predicate,
    d_o.value AS object,
    q.is_inferred
  FROM pgrdf._pgrdf_quads q
  JOIN pgrdf._pgrdf_dictionary d_s ON d_s.id = q.subject_id
  JOIN pgrdf._pgrdf_dictionary d_p ON d_p.id = q.predicate_id
  JOIN pgrdf._pgrdf_dictionary d_o ON d_o.id = q.object_id
  WHERE q.graph_id = 100
    AND d_s.value = 'http://example.com/alice'
  ORDER BY q.is_inferred;

Re-run is safe

sql

SELECT pgrdf.materialize(100);
-- Same result. is_inferred=TRUE rows are dropped + re-emitted.
-- base_triples and the inferred count stay stable.

See Idempotence + operator safety for the contract.

Worked example — subclass chain ​

Setup ​

Materialize ​

Query again ​

Inspect the breakdown ​

Re-run is safe ​

Tests ​