digraph compart{

  edge [fontname="FreeSans",fontsize=10,labelfontname="FreeSans",labelfontsize=10];
  node [fontname="FreeSans",fontsize=10,shape=record];

rankdir=LR;

 U [label="u",height=0.2,width=0.4,color="white", fillcolor="white", style="filled" fontcolor="black"];
 AR1 [label="a,b,r",height=0.2,width=0.4,color="black", fillcolor="white", style="filled" fontcolor="black"]
 U -> AR1 [color="midnightblue",style="solid"]; 
 AR2 [label="a,c,r",height=0.2,width=0.4,color="black", fillcolor="white", style="filled" fontcolor="black"]
 AR1 -> AR2 [color="midnightblue",style="solid",label="y"]; 
 Z [label="z",height=0.2,width=0.4,color="white", fillcolor="white", style="filled" fontcolor="black"];
 AR2 -> Z [color="midnightblue",style="solid"]; 

 
}