FILTER regex prefix filter should ignore "

[niklas88]

In QLever regex prefix filtering needs an escaped " like so FILTER regex(?qlc_name, "^\"state") this isn't conforming to the spec however. The regex should only be applied withing the literal. Thus the regex filter that works in QLever doesn't in Blazegraph. In QLever however we can also use it to efficiently filter IRIs which should still be possible as it can be quite useful.

[niklas88]

I think for the IRI matching we want to support something like FILTER regex(str(?foo), "<bla") where for us str() is almost a no-op but signals we don't want to add the "

[niklas88]

Ok I have now verified that the following FILTER regex() examples work on Blazegraph with Wikidata and I think we should try to make QLever compatible with that syntax.

Standard SPARQL
For IRIs:

FILTER regex(str(?predicate), "^http://www.w3.org/2000/01/rdf-schema#la") .

For Literals

FILTER regex(?name, "^Ala") .

Instead QLever currently needs the following

For IRIs:

FILTER regex(?predicate, "^<http://www.w3.org/2000/01/rdf-schema#") .

For literals:

FILTER regex(?name, "^\"Ala") .

[hannahbast]

Done since #962