$hash={
  'MEX1J' => { 
    'desc' => 'Job 2' 
    'pred' => [TEX1J],
    'succ' => [MEX2J],
  },
  'MEX2J' => { 
    'desc' => 'Job end'
    'pred' => [TEX1J,MEX1J], 
    'succ' => [],
   },
  'TEX1J' => { 
    'desc' => 'Job start'
    'pred' => [], 
    'succ' => [MEX2J],
   }
}