Term types — typed literals, language tags, blank nodes, RDF lists

Turtle ingest preserves the full RDF term-type space: IRIs, plain literals, datatyped literals, language-tagged literals, blank nodes, and RDF collections.

What it does

The Turtle parser round-trips every term species the standard defines:

Term type	Example in Turtle	Stored as
IRI	<http://example.org/alice>	term_type = 1
Plain literal	"hello"	term_type = 2, no datatype tag
Datatyped literal	"42"^^xsd:integer	term_type = 2, datatype IRI in lexical form
Language-tagged literal	"colour"@en-GB	term_type = 2, lang tag in lexical form
Blank node	_:b1 or [ … ]	term_type = 3
RDF collection	( a b c )	Expands to rdf:first / rdf:rest / rdf:nil chain

Why you'd use it

• Data scientists — numeric or language-conditional FILTERs on real data work because the type is preserved at ingest time, not stripped to plain strings.
• Ontologists — load OWL, SHACL, PROV-O and similar vocabularies with confidence that the datatype assertions round-trip.
• Project managers — the on-disk representation matches the W3C spec; no lossy normalisation surprises downstream.

Example

SELECT pgrdf.add_graph(10);

SELECT pgrdf.parse_turtle('
@prefix ex:   <http://example.com/> .
@prefix xsd:  <http://www.w3.org/2001/XMLSchema#> .
@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

ex:alice ex:name "Alice"@en ;
         ex:age  "30"^^xsd:integer ;
         ex:notes [ ex:source "manual" ] ;
         ex:tags  ( "engineer" "rust" "rdf" ) .
', 10);
--  → 8  (4 explicit + RDF list expansion)

Numeric FILTER over a typed literal then works as expected:

SELECT * FROM pgrdf.sparql(
  'PREFIX ex:  <http://example.com/>
   PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
   SELECT ?s ?a
     WHERE { ?s ex:age ?a FILTER(?a >= 18) }');
--  → {"s": "http://example.com/alice", "a": "\"30\"^^xsd:integer"}

Language tag FILTER:

SELECT * FROM pgrdf.sparql(
  'PREFIX ex: <http://example.com/>
   SELECT ?n WHERE { ?s ex:name ?n FILTER(LANG(?n) = "en") }');

Tests

• tests/regression/sql/21-typed-literals.sql
• tests/regression/sql/22-lang-tags.sql
• tests/regression/sql/23-blank-nodes.sql
• tests/regression/sql/24-rdf-list.sql
• tests/w3c-sparql/17-lang-tag/
• tests/w3c-sparql/21-numeric-filter/

See also

• Hexastore + dictionary.
• FILTER expressions.