Externally-described data structure

Specify either the EXT keyword or the EXTNAME keyword as the first keyword.

DCL-DS myfile EXT END-DS;
DCL-DS extds1 EXTNAME('MYFILE') END-DS;

If you specify the EXT keyword, you can also specify the EXTNAME keyword as a later keyword.

DCL-DS extds2 EXT INZ(*EXTDFT) EXTNAME('MYFILE') END-DS;