numeric classyscale, classxscale ;

classyscale := 2cm ;
classxscale := 3.5cm ;

vardef class ( expr name, x, y ) =
  save p, q ;
  path p, q, pd, qd ;

  pickup pencircle scaled 0.8pt ;
  pd := fullcircle xscaled classxscale yscaled classyscale ;
  qd := pd shifted (x + 5pt, y);
  fill qd withcolor black ;
  draw qd ;  
  p := fullcircle xscaled 3.5cm yscaled 2cm ;
  q := p shifted (x, y) ;
  fill q withcolor 0.7white ;
  label(name, center q) withcolor blue ;
  draw q;
  q
enddef ;

def inheritfrom ( expr child, parent, n ) =
  save p ;
  pair a, b ;
  path p ;
  pickup pencircle scaled 3pt ;
  a := point n of parent shifted (0, -5pt) ;
  b := point 2 of child shifted (0, 5pt) ;
  p := b -- unitvector (a) ;
  draw p ;
enddef ;