changeAttributes(ident id, ident groupId, string day, string time, string location, integer maxSize) {
  assume exists //exercises/exercise[id]/groups/group[groupId]; # implicitly true in OO implementations
 
  update //exercises/exercise[id]/groups/group[groupId]/day day;
  update //exercises/exercise[id]/groups/group[groupId]/time time;
  update //exercises/exercise[id]/groups/group[groupId]/location location;
  update //exercises/exercise[id]/groups/group[groupId]/maxSize maxSize;
}