docs: add sparql-quirks.md with the GRAPH/OPTIONAL gotcha#107
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Captures the RDF4J semantics for `GRAPH ?x { OPTIONAL { ... } }` —
it returns zero solutions when the inner pattern is unmatched, so the
surrounding row is filtered out even though the inner pattern is
optional. Workaround: `OPTIONAL { GRAPH ?x { ... } }`.
Bit a nanodash spaces-repo consumer twice
(see knowledgepixels/nanodash#468). Putting the note here so the next
person doesn't lose an afternoon to the same trap.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
For complex consumer queries (multiple cross-graph joins + a UNION inside GRAPH ?g), resolving the npa:hasCurrentSpaceState pointer with a variable ?g can trigger an RDF4J planner blow-up that 504s — where the same query with a hardcoded state-graph IRI runs in under a second. The materialiser doesn't hit this because it formats the IRI as a Java string, not a SPARQL variable; the trap is specific to consumers that follow the documented pointer-resolution pattern verbatim. Documents the workaround (resolve once, inline the constant) without proposing a server-side fix — the planner behaviour is what it is, and the recommended pattern still works for the simple cases that dominate. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Adds
doc/sparql-quirks.mdwith two RDF4J/SPARQL traps encountered while building consumer queries against/repo/spacesfor nanodash (knowledgepixels/nanodash#468):GRAPH ?x { OPTIONAL { ... } }drops the row when the inner pattern is unmatched — pull the OPTIONAL outside. Bit nanodash twice.npa:hasCurrentSpaceStatepointer pattern can blow up the planner when the pattern underGRAPH ?ghas multiple cross-graph joins + a UNION — same query with a hardcoded state-graph IRI runs in well under a second; the variable-?g form 504s after 60s. Materialiser code isn't affected (it formats the IRI as a Java string), but consumers that follow the documented pattern verbatim can hit it.Happy to move the file or restructure if there's a better spot —
CONTRIBUTING.md? A "Consumer notes" section indesign-space-repositories.md?Test plan
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