CONSTRUCT 
  { ?x ?p1 ?o1 .
    ?x ?p2 ?y .
    ?y ?p3 ?o2 .}
WHERE
  { ?x  <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>  <thing> ;
        ?p1                   ?o1 .
    OPTIONAL
      { ?x  ?p2  ?y .
        ?y  ?p3  ?o2 .
      }
  }