ql:has-pattern should be used automatically if possible

[niklas88]

In SPARQL queries where there is a triple of the form

…
?subj ?predicate ?object .
…

and ?object appears nowhere else we should automatically replace it with

…
?subj ql:has-predicate ?predicate .
…

unless QLever was started with --no-patterns. This would allow completion queries to be standard SPARQL while automatically triggering our pattern trick and pattern scan techniques.

One remaining problem is that with --no-patterns unconstrained predicates would stop working instead of just being really slow.

[hannahbast]

It's a good idea, but note that you are changing the result set of the query. If you have one subject with one predicate and k objects and you "SELECT ?predicate" then: 1. The first query gives you a result with k rows, all containing the same predicate 2. The second query gives you a result with one row It would of course be desirable to extend the pattern trick to also include information about the number of objects per predicate, but if you think about it this goes directly against the idea that make the pattern trick efficient in the first place. The results would be the same though with a "SELECT DISTINCT ?predicate"

…

On 07.03.2019 15:44, Niklas Schnelle wrote: In SPARQL queries where there is a triple of the form |… ?subj ?predicate ?object . … | and |?object| appears nowhere else we should automatically replace it with |… ?subj ql:has-predicate ?predicate . … | unless QLever was started with |--no-patterns|. This would allow completion queries to be standard SPARQL while automatically triggering our pattern trick and pattern scan techniques. One remaining problem is that with |--no-patterns| unconstrained predicates would stop working instead of just being really slow. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#203>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ANUinILEdPfynggMLQobj1UTvuEx7mIGks5vUSXVgaJpZM4bjW2l>.

[niklas88]

This has been implemented with #245