digraph G {
  node [shape=plaintext]
  subgraph cluster_0 {
    label = "EMP"
    empno
    sal
    hiredate
    comm
  }
  subgraph cluster_1 {
    label = "JOB"
    job
    ename
  }
  subgraph cluster_2 {
    label = "DEPT"
    deptno
    loc
    dname
  }
  subgraph cluster_3 {
    label = "PROJ"
    projno
    pname
    budget
  }
  EMP -> JOB
  JOB -> DEPT
  DEPT -> PROJ
}