SPARQL regex for literal returns nothing even with "match any character"

Support
1

I'm playing with the music dataset and trying to get REGEX to work in SPARQL queries.

I can do a simple query like:

prefix : <http://stardog.com/tutorial/>
SELECT ?soloartist
WHERE {
   <http://stardog.com/tutorial/ABBA> :member ?soloartist .
}

And predictably get results like this: Screenshot by Lightshot

But any kind of regex search, including "give me any character whatsoever" gives me 0 triples in return.

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

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

This is also true when the regex is a perfect match:

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

or just has one letter that is expected to be in the returned triple

FILTER(REGEX(?band, "A", "i"))

I've double checked my quotation marks. Is there something Stardog specific I'm not understanding?

2

Hi Susanne,

REGEXs don't work on URIs, only strings. That's why your second code block is returning no results. If you change it to this, it'll work:

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

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

You might think this means your third code block should become this:

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

(I say this because this is what I tested initially.) However, when ?band gets converted to a string, the angle brackets are not included in the result. In other words, str(<http://stardog.com/tutorial/ABBA>) gives "http://stardog.com/tutorial/ABBA". Therefore, your third code block should be:

FILTER(REGEX(?band, "http://stardog.com/tutorial/ABBA", "i"))

Best,
Steve

3

Thank you Steve, that makes a lot of sense!