Graph-query conformance suite finds silent semantic splits across engines
A new executable GPML reference finds multiple engines can accept the same path pattern yet return different endpoint-pair multisets—without an error.
A new conformance suite for the graph pattern-matching language shared by GQL and SQL/PGQ finds that apparently valid path queries can produce different answers across shipping engines. The authors’ 17-construct test reports that five external engines differ from its executable reference on seven constructs; across all disagreements, 15 of 26 were silent, meaning the query returned a different multiset without raising an error. That puts the reported silence ratio at 0.58. The paper and artifact were released publicly.
This is a correctness benchmark, not a speed race
The suite covers path modes and restrictors, quantified segments, selectors, direction, parallel edges and self-loops. Each case is scored as conforming, diverging, rejected or inexpressible, based on an exact comparison of endpoint-pair multisets. Every cell was repeated three times to check determinism, according to the generated results.
The evaluated releases are Kùzu 0.11.3, DuckPGQ on DuckDB 1.4.1, Neo4j 5.26.30 and 2026.04.0, Memgraph 5.9.0, and Apache AGE 1.8.0. The project also reports Samyama-Graph 1.8.0 but excludes that engine from aggregates because the authors develop it and its release incorporated fixes prompted by the suite.
The reference implementation is not a majority vote among products. It encodes the standard’s GPML path semantics and must reproduce six worked answers from the standards committee’s reference exposition before engines are measured. That gate caught a bug in the authors’ first implementation, according to the repository documentation.
Not every difference is an implementation bug
The artifact’s second scoring pass compares each divergence with the path mode declared in that engine’s own documentation. Of 15 answer divergences in the aggregate map, nine are documented language differences; the remaining six are departures from the standard implemented by the relevant engine. Separately, oracle-free metamorphic checks report 39 self-consistency violations across six graph fixtures, attributed to Kùzu and DuckPGQ in the published results.
The practical signal is narrower—and more useful—than a conventional leaderboard rank: syntax compatibility does not guarantee answer compatibility. A workload moved between graph engines can keep running while changing its result, especially around path repetition and selection semantics.
There are important limits. This is a small semantic-conformance suite, not a broad workload benchmark. Its headline map compares endpoint-pair multisets rather than full path bindings, and it contains no latency or throughput measurements. Results are also tied to the named versions. Still, the repository includes the reference implementation, fixtures, adapters, expected outputs and minimal reproducers, making each reported mismatch inspectable rather than leaving it as a paper-only claim.
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