PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

ASK WHERE {
  <http://rdfa.info/test-suite/test-cases/rdfa1.1/html5/0284.html> rdf:value " 2012-03-18"^^xsd:dateTime .
}
