The ACCESS MODE clause specifies the order of access for a file's
  records.

  Format 2 - Relative File

                      {  SEQUENTIAL [ RELATIVE KEY IS rel-key ] }
   [ ACCESS MODE IS ] { { RANDOM  }   RELATIVE KEY IS rel-key   }
                      { { DYNAMIC }                             }

1  –  rel-key

  is the file's RELATIVE KEY data item.