SPARQL 1.1 query service wrapping pub/sub triples interface
Add a backend-agnostic SPARQL query service that parses SPARQL
queries using rdflib, decomposes them into triple pattern lookups
via the existing TriplesClient pub/sub interface, and performs
in-memory joins, filters, and projections.
Includes:
- SPARQL parser, algebra evaluator, expression evaluator, solution
sequence operations (BGP, JOIN, OPTIONAL, UNION, FILTER, BIND,
VALUES, GROUP BY, ORDER BY, LIMIT/OFFSET, DISTINCT, aggregates)
- FlowProcessor service with TriplesClientSpec
- Gateway dispatcher, request/response translators, API spec
- Python SDK method (FlowInstance.sparql_query)
- CLI command (tg-invoke-sparql-query)
- Tech spec (docs/tech-specs/sparql-query.md)
New unit tests for SPARQL query
