How to handle case-insensitive SPARQL data in MarkLogic

Question

I'm trying to understand how best to handle literals in Marklogic SPARQL data which may be in any case. I'd like to be able to do a case insensitive search but I believe that isn't possible with semantic queries. For a simplistic example I want:

SELECT *
WHERE { ?s ?p "Red"}

and

SELECT *
WHERE { ?s ?p "red"}

to return all values whether the object is "Red", "RED", "red" or "rED".

My data is from another source which has variable capitalisation rules. At the moment the only thing I can think of is to add an extra triple which always contains the text in lower case so I can always search on that value. Alternatively, would it make sense to create some new range query in MarkLogic with a case insensitive collation (if that's possible on triple data)?

Answer 1

You could use a filter that ignores case.

select * where {
  ?s ?p ?o
  FILTER (lcase(str(?o)) = "red")
}

Based on the answer to another question.

Edit: I asked Steve Buxton, MarkLogic's PM for semantics features, and he suggested this:

let $store := sem:store( (), cts:element-value-query(xs:QName("sem:object"), "red", "case-insensitive") )
return
  sem:sparql('
    SELECT ?o
    WHERE {
      ?s ?p ?o
      FILTER (lcase(str(?o)) = "red")
    }', (), (), $store
 )

sem:store is a MarkLogic 8 (now available through Early Access) function that selects a group of triples. The SPARQL query then runs on the reduced set, limiting the number of triples that need to be filtered.