SPARQL & RDF interface¶

epistemic-graph is an RDF triple-store: you load RDF (OWL/RDFS or plain triples), the engine maps it onto the property graph, and SPARQL SELECT runs over it. RDF and the property graph are the same data — a triple is a node, an edge, or a property depending on its object.

Status snapshot: SPARQL SELECT/ASK/CONSTRUCT/DESCRIBE, UPDATE, true named graphs, and the W3C /sparql HTTP endpoint (feature sparql-http) are all supported. Content negotiation, rich FILTER, sub-SELECT, SERVICE federation, MINUS, negated property sets (!p), ORDER BY/VALUES/EXISTS, FROM/FROM NAMED, and an SPO/POS index with selectivity join-ordering are shipped (EG-050..057, EG-KG.ontology.order-by-values-exists/135). GeoSPARQL + RCC8/Egenhofer (EG-KG.ontology.concept-10/155), the full RDF serialization matrix (JSON-LD/TriG/N-Quads/RDF-XML, EG-KG.ontology.eg-concrete-syntax-matrix/137), SHACL/ShEx/ICV validation (EG-KG.ontology.concept-6/133/146), and OBDA/R2RML virtual graphs (EG-101) are also in. See the capability matrix.

RDF ↔ property-graph mapping¶

RDF construct	Maps to
IRI / blank-node subject or object	a graph node (id = canonical term string)
triple with a resource object `(s, p, o)`	a typed edge `s --p--> o`
triple with a literal object	a property on `s` (value + datatype + lang preserved)
`rdf:type`	folded into the node `type` property and kept as an explicit typing edge
named graph	a `GraphCore` in the registry with a `:NamedGraph` marker

Multi-valued literals for the same predicate are stored under the reserved __rdf_multivalue_literals typed property in the authoritative node image. LoadReport.multivalue counts the additional values, and export round-trips them to N-Triples by set equality without a secondary store.

SPARQL SELECT¶

SELECT ?s ?o WHERE {
  ?s rdfs:subClassOf ?o .
  FILTER (?s != ?o)
}
ORDER BY ?s
LIMIT 100

Implemented algebra (compiled to scans over the property graph, not an embedded triple evaluator):

Patterns: BGP, property paths (^p, p/q, p|q, p+, p*, p?, negated !p — EG-KG.ontology.negated-property-set), OPTIONAL, UNION, MINUS (EG-KG.ontology.minus), sub-SELECT (EG-KG.ontology.sub-select), SERVICE federation (EG-KG.query.sparql-service-federation-client), VALUES inline data.
Solution modifiers: Project, Distinct, Reduced, Slice (LIMIT/OFFSET), ORDER BY (multi-key ASC/DESC with SPARQL term ordering, incl. top-k ORDER BY … LIMIT — EG-KG.ontology.order-by-values-exists/135), Group + aggregates (COUNT/SUM/AVG/MIN/MAX/GROUP_CONCAT/SAMPLE), BIND, FROM/FROM NAMED dataset scoping (EG-KG.ontology.from-from-named).
FILTER (rich — EG-KG.ontology.rich-filter/127): arithmetic, REGEX, IN, EXISTS/NOT EXISTS, STR/LANG/LANGMATCHES/ DATATYPE/BOUND, isIRI/isLiteral/isBlank/isNumeric, string funcs (CONTAINS/STRSTARTS/STRENDS/STRLEN/SUBSTR/UCASE/LCASE/CONCAT/STRBEFORE/STRAFTER/REPLACE), hashes (MD5/SHA*), date-time (NOW/YEAR…/TZ), numeric (RAND/ABS/ROUND/CEIL/FLOOR), term constructors (IRI/BNODE/STRDT/STRLANG/UUID), COALESCE, IF, with datatype-aware comparison.

Query execution uses hashed SPO/POS/PSO indexes over the snapshot with cardinality-based BGP reordering (EG-KG.ontology.capability-catalog) — no longer a full scan per triple pattern.

ASK returns a boolean; CONSTRUCT instantiates its template; DESCRIBE returns a concise bounded description. UPDATE (INSERT/DELETE DATA, DELETE/INSERT WHERE, CLEAR, CREATE/DROP GRAPH, and the graph-management COPY/MOVE/ADD — EG-134) mutates the graph through a GraphStore; LOAD is intentionally unsupported (the write path does no HTTP fetch).

Content negotiation & serialization matrix (EG-KG.ontology.content-negotiation-serializers/136/137)¶

/sparql is Accept-aware, with a per-form default and an output=/format= override:

SELECT/ASK → SPARQL-results JSON / XML / CSV / TSV.
CONSTRUCT/DESCRIBE → Turtle, N-Triples, and — completing RDF 1.1 — JSON-LD 1.1 (expansion/ compaction, @id/@type/@graph), TriG + N-Quads (named-graph-aware), and RDF/XML.

The same matrix is available on ingest (parse) and via the W3C SPARQL 1.1 Graph Store Protocol (GET/PUT/POST/DELETE on /rdf-graphs/…?graph=, EG-134) for direct RDF-tooling read/write.

SPARQL UPDATE and Graph Store PUT/POST/DELETE require an exact current request envelope: Authorization: Bearer eg2.<envelope> and X-Epistemic-Request-Id. The adapter dispatches that signed request into the native multi-graph coordinator. It checks every addressed graph before detached planning and creates missing graphs only with graph:admin. Before changing graph or lifecycle state, it durably prepares an authenticated, encrypted recovery plan that contains complete before/after graph images. Cross-shard spans commit through retained-decision 2PC; local and single-group spans use deterministic child MutationBatch records. A failure durably selects compensation, replays the complete preimages, and removes graphs created by the update. Restart always resumes the recorded direction before an acknowledgement is returned. The HTTP adapter has no direct live-core write path.

GeoSPARQL — spatial SPARQL (EG-KG.ontology.concept-10/155, feature `geosparql`)¶

The geo:/geof: vocabulary, WKT/GML geometry literals, and topological FILTER functions lower onto the eg-geo spatial predicates (see gis):

Baseline (EG-KG.ontology.concept-10): geof:sfWithin/sfIntersects/distance.
RCC8 (EG-KG.ontology.concept-7): geof:rcc8eq/dc/ec/po/tpp/ntpp/tppi/ntppi.
Egenhofer (EG-KG.ontology.concept-7): geof:ehEquals/disjoint/meet/overlap/covers/coveredBy/inside/contains.

SELECT ?site WHERE {
  ?site geo:hasGeometry/geo:asWKT ?g .
  FILTER (geof:sfWithin(?g, "POLYGON((…))"^^geo:wktLiteral))
}

Validation — SHACL / ShEx / ICV¶

SHACL (EG-KG.ontology.concept-6, crate eg-shacl): node/property shapes, sh:targetClass/targetNode, cardinality/datatype/pattern/sh:in/logical + SPARQL-based constraints → an sh:ValidationReport via Method::ShaclValidate.
ShEx (EG-KG.compute.concept-2): shape-expression schema validation (shape refs, triple constraints, cardinality, node constraints, AND/OR/NOT) via Method::ShexValidate.
ICV (EG-KG.ontology.wired-into-commit-write): Stardog-style Integrity Constraint Validation — interpret SHACL shapes under the closed-world / unique-name assumption as database integrity constraints, report violations with a focus-node + failing-constraint + a SPARQL "explain" witness, with an optional guard mode that rejects a write/transaction that would violate a constraint (and also runs in the OWL-reasoned view).

OBDA / virtual graphs — R2RML (EG-101)¶

R2RML-style :TriplesMap mappings (logicalSource → subject/predicate/object templates) expose a foreign/relational source (via the EG-073 ForeignSource registry) as a virtual RDF graph: SPARQL over the virtual graph rewrites to an Op::ForeignScan against the backing source — no materialization.

How it's reached¶

SPARQL is served two ways: the W3C /sparql HTTP endpoint (src/server/sparql_http.rs, feature sparql-http — GET ?query=, POST application/sparql-query/application/sparql-update, content-negotiated output), and the binary RPC method (Method::Sparql) with result-cache + RLS row-filtering. Companion RDF methods: AddTriples (durable, replicated), GetRdf (serialization-matrix export), and the validation methods above. SERVICE fan-out obeys the EPISTEMIC_GRAPH_SPARQL_SERVICE_ALLOW SSRF allowlist (fail-closed by default).

Reasoning¶

Loaded ontologies are reasoned over by the OWL 2 EL⁺/RL engine — see the ontology lifecycle guide.