PREFIX dc:   <http://purl.org/dc/elements/1.1/>
PREFIX :     <http://example.org/book/>
PREFIX ns:   <http://example.org/ns#>

SELECT ?book ?title ?price
{
    ?book dc:title ?title ;
          ns:price ?price .
    VALUES (?book ?title)
    {
        (UNDEF "SPARQL Tutorial")
        (:book2 UNDEF)
    }
}