prjtree.dot

digraph G {
	compound = true;
        size = "3.5,3.0";
        margin = "0.1";
	node [ shape = box, style=filled,
          color = lightblue, fontcolor = black, fontsize=12 ];

	{
		root [ label = "Root project", width = 2.0 ];
	}
	{ rank = same ; root };

	{
		ss_a [ label = "Subsystem A", width = 2.0 ];
		ss_b [ label = "Subsystem B", width = 2.0 ];
	}
	{ rank = same ; ss_a; ss_b }
	root -> ss_a;
	root -> ss_b;

	{
		sa1 [ label = "A1" ];
		sa2 [ label = "A2" ];
		sa3 [ label = "A3" ];

		sb1 [ label = "B1" ];
		sb2 [ label = "B2" ];
		sb3 [ label = "B3" ];
	}
	{ rank = same ; sa1; sa2; sa3; sb1; sb2; sb3 };
	ss_a -> sa1;
	ss_a -> sa2;
	ss_a -> sa3;

	ss_b -> sb1;
	ss_b -> sb2;
	ss_b -> sb3;

	{
		common [ label = "Common", width = 2.0 ];
	}

	sa1 -> common;
	sb3 -> common;
}