SPARQL: Result Formats

purrdf-sparql-results is the results boundary of the SPARQL stack: the canonical authority for turning a SparqlResult (SELECT solutions, ASK boolean, or CONSTRUCT graph) into the four W3C SPARQL Results formats — JSON (SRJ), XML, CSV, and TSV — plus an additive, provenance-carrying PurRDF extension where the format can carry one. JSON and XML documents can also be read back (from_json, from_xml).

use purrdf::sparql::{serialize, ResultProvenance, SparqlResultsFormat};

// `result` is the SparqlResult produced by purrdf-sparql-eval (or any engine
// implementing the purrdf-core SparqlEngine seam).
let outcome = serialize(&result, SparqlResultsFormat::Json, &ResultProvenance::default())
    .expect("SELECT serializes to SRJ");

assert!(!outcome.provenance_dropped);
let json = String::from_utf8(outcome.bytes).unwrap();

Per-format writers (to_json, to_xml, to_csv, to_tsv) and readers (from_json, from_json_boolean, from_xml, from_xml_boolean) are also exported directly.

Behavior worth knowing before you pick a format

• Byte-deterministic output — the same result always serializes to the same bytes, like every other PurRDF output path (Codecs & Determinism).
• The support matrix is enforced, not fudged — XML rejects CONSTRUCT graphs, and CSV/TSV reject both ASK booleans and CONSTRUCT graphs, each as a typed Error::Format, rather than emitting something spec-shaped but wrong.
• Lossy projections are flagged — CSV/TSV have no extension point, so a populated provenance is trimmed at the exit gate and SerializeOutcome::provenance_dropped is set; the drop is never silent.

The provenance extension

The PurRDF extension is additive: a standard SPARQL results consumer can read the JSON/XML documents unchanged, while a PurRDF-aware consumer can recover per-result provenance carried alongside the bindings. Where the format has no extension point (CSV/TSV), the provenance is dropped loudly, per the loss discipline described in Slices, Mappings & Provenance.

One term-syntax authority

The crate depends only on purrdf-core and stays wasm-clean; term and N-Triples syntax come exclusively from the kernel’s emit primitives, so there is exactly one term-syntax authority in the workspace — results, codecs, and diagnostics can never disagree about how a term is written.

Related

• SPARQL: Querying — producing the SparqlResult in the first place.
• docs.rs/purrdf-sparql-results — the full API reference.