A sort-merge file description entry describes a sort or merge file's
  physical structure, identification, and record names.

  Format -

  SD file-name

    [RECORD { CONTAINS [shortest-rec TO] longest-rec CHARACTERS        }]
    [       { IS VARYING IN SIZE [FROM shortest-rec] [TO longest-rec]
                              CHARACTERS [DEPENDING ON depending-item] }]

    [DATA { RECORDS ARE } {rec-name} ... ]
    [     { RECORD IS   }                ] .