var graph = "{'A':['B','D'],'B':['C']}, 'E':[]";
var node_relations = "{
  'A':{'children':['B','D'],'parents':[]},
  'B':{'children':['C'],'parents':['A']},
  'C':{'children':[],'parents':['B']},
  'D':{'children':[],'parents':['A']},
  'E':{'children':[],'parents':[]}
}";