changeAttributes(ident id, string title, string date, string time, string location) {
  assume exists //exams/exam[id]; # implicitly true in OO implementations
 
  update //exams/exam[id]/title title;
  update //exams/exam[id]/date date;
  update //exams/exam[id]/time time;
  update //exams/exam[id]/location location;
} # roles: admin, examiner[id]