The Lucene connector documentation for GraphDB (https://graphdb.ontotext.com/documentation/enterprise/lucene-graphdb-connector.html#usage) mentions at some point "The minimum required ruleset level in GraphDB is RDFS."
Why is this a mandatory prerequisite for using Lucene? For performance reasons, I have projects that would need "No inference" in the repository ruleset option, but still would like to benefit from the Lucene search engine - how exactly is Lucene dependant on RDF?
The RDFS ruleset is required for the specific example and dataset. You could absolutely use it with empty ruleset if needed.