The OPEN statement creates an access stream to the file, makes the file
  available to the program, begins the processing of a file, and
  specifies file sharing.

  Format 1 - Sequential, Relative, Indexed

      {        {                         [WITH LOCK              ]}   }
      {        {                         [         {NO OTHERS   }]}   }
      {        {                         [         {{|READERS |}}]}   }
      {{INPUT }{file-name[WITH NO REWIND][ALLOWING {{|WRITERS |}}]}...}
      {{OUTPUT}{                         [         {{|UPDATERS|}}]}   }
      {        {                         [         {ALL         }]}   }
  OPEN{                                                               }...
      {        {                    [WITH LOCK                  ]}    }
      {        {                    [         { NO OTHERS     } ]}    }
      {        {                    [         { {| READERS  |}} ]}    }
      {{EXTEND}{ file-name          [ALLOWING { {| WRITERS  |}} ]}... }
      {{I-O   }{                    [         { {| UPDATERS |}} ]}    }
      {        {                    [         { ALL           } ]}    }

1  –  file-name

  is the name of a file described in the Data Division.  It cannot be
  the name of a sort or merge file.