function graph_properties(graph::DAG)
   # make sure the graph is fully generated
   apply_all!(graph)

   d = 0
   ce = 0
   ed = 0
   for node in graph.nodes
      d += data(node.task) * length(node.parents)
      ce += compute_effort(node.task)
      ed += length(node.parents)
   end

   ci = ce / d

   result = (data = d,
             compute_effort = ce,
             compute_intensity = ci,
             nodes = length(graph.nodes),
             edges = ed)
   return result
end

function get_exit_node(graph::DAG)
   for node in graph.nodes
      if (is_exit_node(node))
         return node
      end
   end
   @assert false "The given graph has no exit node! It is either empty or not acyclic!"
end