freetext search in dbpedia - sparql

Question

I want to use freetext search against the dbpedia and I'm trying the query I found on the W3C website: https://www.w3.org/2009/Talks/0615-qbe/
If I try the query WITHOUT the bif: prefix by commenting it out I get the error shown below the query:
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX type: <http://dbpedia.org/class/yago/>
PREFIX prop: <http://dbpedia.org/property/>
# PREFIX bif: <http://www.openlinksw.com/schemas/bif#>
SELECT ?lbl ?est
WHERE {
?country rdfs:label ?lbl .
FILTER(bif:contains(?lbl, "Republic")) .
?country a type:Country108544813 ;
prop:establishedDate ?est .
FILTER(?est < "1920-01-01"^^xsd:date) .
}
Error: Line 9, Parse error: namespace mapping for "bif" not defined
when expanding QName "bif:contains".
[condition type: sparql-lexer-error-namespace-mapping-not-defined]
well: that makes sense, you do need to define your namespace. So let me do the same query again using the bif: prefix that I found on the Virtuoso website (and various other places)
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX type: <http://dbpedia.org/class/yago/>
PREFIX prop: <http://dbpedia.org/property/>
PREFIX bif: <http://www.openlinksw.com/schemas/bif#>
SELECT ?lbl ?est
WHERE {
?country rdfs:label ?lbl .
FILTER(bif:contains(?lbl, "Republic")) .
?country a type:Country108544813 ;
prop:establishedDate ?est .
FILTER(?est < "1920-01-01"^^xsd:date) .
}
Now I get a different error: it seems that the bif: namespace is a protected name by Virtuoso
So it seems I cannot live with bif: or without :bif. Has anyone seen this error before? Thanks.
Btw: I really don't care that much about bif: What I really want is to do freetext queries against dbpedia. So any alternative is welcome. YES: there are earlier questions on SO about this but note that each of those answers contain bif: as well.
Added later: so just to be sure I changed bif: into bof: and now I get a new error that shows that contains no longer is a valid operator. See below. So anyway: I guess the only thing I care about from here on is: how do you do freetext queries against dbpedia :-)

Answer 1

bif: is a Virtuoso built-in, for "built-in function".
You're going through some sort of SPARQL pre-parser, not directly against the SPARQL endpoint, so you do need to define the prefix in your query. Most such pre-parsers will do the right thing if you just --
PREFIX bif: <bif:>
Alternatively, you can change your query from using the bif:contains function --
FILTER(bif:contains(?lbl, "Republic"))
-- to use SPARQL regex --
FILTER regex(?lbl, "Republic")