Why isn't the regex in my query returning any results?

Created by Steve Place, Modified on Fri, 06 Oct 2023 at 09:36 AM by Steve Place

When using regexes in SPARQL, a common cause of error is to search for URIs rather than strings. Using a regex over a URI is not possible in SPARQL, so you would convert a query like this:

prefix : <http://stardog.com/tutorial/>

SELECT *
WHERE {
   ?band :member ?soloartist 
    FILTER ( REGEX(?band, ".*" ) )
}

to this:

prefix : <http://stardog.com/tutorial/>

SELECT ?soloartist ?band
WHERE {
   ?band :member ?soloartist 
    FILTER ( REGEX(str(?band), ".*" ) )
}

Once this issue is solved, a common pitfall is to include angle brackets in the regex pattern, like this:

FILTER(REGEX(str(?band), "<http://stardog.com/tutorial/The_Beatles>"))

The problem with this is that the angle brackets are not included in the string representation of a URI. Instead, you would filter for The Beatles like so:

FILTER(REGEX(str(?band), "http://stardog.com/tutorial/The_Beatles"))