PREFIX att: <http://example.org/attendance/>
PREFIX ev: <http://example.org/events/>

SELECT ?name 

FROM <http://www.w3.org/TR/grddl-primer/events.rdf>
FROM <http://www.w3.org/TR/grddl-primer/attendance.rdf>

WHERE
{
  ?event ev:label "choose new meeting location" .
  ?event ev:date ?date .
  ?attendance att:date ?date .
  ?attendance att:name ?name .
  ?attendance att:present "y" .
}