digraph G {
    a -> b;
    a -> c;
    a -> d;
}

graph {
    a -- b -- c;
    b -- d;
}

digraph G {
    a -> b -> c;
    b -> d;
}

digraph G {
    // label属性可以改变节点显示的名称
    a [label = "Foo"];
    // shape属性可以改变节点的形状
    b [shape = box];
    // color指定连接线的颜色
    a -> b -> c [color = blue];
    // style指定连接线的风格
    b -> d [style = dotted];
}

digraph {
    a -> b [dir = both];
    b -> c [dir = none];
    c -> d [dir = back];
    d -> a [dir = forward];
}

digraph {
    // 统一将下面的节点设置成矩形
    node [shape = box];
    // n/e/s/w分别表示north, east, south, west, 可组合使用
    c1:n  -> d1    [label=n];
    c2:ne -> d2:ne [label=ne];
    c3:e  -> d3:ne [label=e];
    c4:se -> d4:n  [label=se];
    c5:s  -> d5:n  [label=s];
    c6:sw -> d6:n  [label=sw];
    c7:w  -> d7:nw [label=w];
    c8:nw -> d8:nw [label=nw];
}