dot/trpl17-01.dot

digraph {
   dpi = 300.0;
   
   rankdir = "LR";
   
   // makes ordering between subgraphs work
   newrank = true;
   
   node [shape = diamond;];
   
   subgraph cluster_task_a {
      label = "Task A";
      
      A1;
      A2;
      A3;
      A4;
      
      A1 -> A2 -> A3 -> A4 -> A0 [style = invis;];
      
      // for vertical alignment purposes only
      A0 [style = invis;];
      
      // Makes the heights line up between the boxes.
      A4 -> A0 [style = invis;];
   }
   
   subgraph cluster_task_b {
      label = "Task B";
      
      B0 [style = invis;];
      
      B1;
      B2;
      B3;
      
      B0 -> B1 -> B2 -> B3 [style = invis;];
   }
   
   A1 -> B1 -> A2 -> B2 -> A3 -> A4 -> B3;
}