SPARQL: Filter

PREFIX rss:   <http://purl.org/rss/1.0/>
PREFIX xsd:   <http://www.w3.org/2001/XMLSchema#>
PREFIX  dc:   <http://purl.org/dc/elements/1.1/>
SELECT ?item_title ?pub_date
WHERE {
      ?item rss:title ?item_title .
      ?item dc:date ?pub_date .
      FILTER xsd:dateTime(?pub_date) >= "2005-04-01T00:00:00Z"^^xsd:dateTime &&
             xsd:dateTime(?pub_date) < "2005-05-01T00:00:00Z"^^xsd:dateTime
      }