Format

            [ BASED ON field-name                                ]
            [                                                    ]
            [             {BIT       }                           ]
            [             {BYTE      }                           ]
            [ ALIGNED  ON {WORD      } BOUNDARY                  ]
            [             {LONGWORD  }                           ]
      name  [             {QUADWORD  }                           ] .
            [             {OCTAWORD  }                           ]
            [                                                    ]
            [ CONSTRAINT constr-name NOT NULL [DEFERRABLE      ] ]
            [                                 [NOT DEFERRABLE  ] ]
            [                                                    ]