def CoefficientOfNetworkComplexity_metric(bpmn_graph):
    """
    Returns the value of the Coefficient of Network Complexity metric
    ("Ratio of the total number of arcs in a process model to its total number of nodes.")
    for the BPMNDiagramGraph instance.

    :param bpmn_graph: an instance of BpmnDiagramGraph representing BPMN model.
    """

    return float(len(bpmn_graph.get_flows())) / float(len(bpmn_graph.get_nodes()))