Dbpedia sparql gives empty result to my query, what is wrong?

Question

I'm doing sparql query in this site. It gives me an empty result, what is wrong with my query?

prefix foaf:    <http://xmlns.com/foaf/0.1/>
select * where {
?s rdf:type foaf:Person.

} LIMIT 100

This query is ok, but when I add the second pattern, I got empty result.

?s foaf:name 'Abraham_Robinson'.

prefix foaf:    <http://xmlns.com/foaf/0.1/>
select * where {
?s rdf:type foaf:Person.
?s foaf:name 'Abraham_Robinson'.
} LIMIT 100

How to correct my query so the result includes this record:

http://dbpedia.org/resource/Abraham_Robinson

Answer 1

I guess Kingsley misread this as a freetext search, rather than a simple string comparison.

The query Kingsley posted and linked earlier delivers no solution, for the same reasons as the original query failed, as identified in the comment by AKSW, i.e. --

• foaf:name values don't generally replaces spaces with underscores as in the original value; i.e., 'Abraham_Robinson' should have been 'Abraham Robinson'
• foaf:name strings are typically langtagged, and it is in this case, so that actually needs to be 'Abraham Robinson'@en

Incorporating AKSW's fixes with this line ?s foaf:name 'Abraham Robinson'@en., the query works.

All that said -- you may prefer an alternative query, which will deliver results whether or not the foaf:name value is langtagged and whether or not the spaces are replaced by underscores. This one is Virtuoso-specific, and produces results faster because the bif:contains function uses its free-text indexes, would be --

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>
SELECT * 
WHERE
  {
    ?s     rdf:type      foaf:Person ;
           foaf:name     ?name .
    ?name  bif:contains  "'Abraham Robinson'" . 
  } 
LIMIT 100

Generic SPARQL using a REGEX FILTER works against both Virtuoso and other RDF stores, but produces results more slowly because REGEX does not leverage the free-text indexes, as in --

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>
SELECT * 
WHERE
  {
    ?s     rdf:type      foaf:Person ;
           foaf:name     ?name .
    FILTER ( REGEX ( ?name, 'Abraham Robinson' ) ) . 
  } 
LIMIT 100