EXT marks a free-format DCL-DS externally described - the free-form
equivalent of the E in position 22 of a fixed-format D-spec. Used on its own
it names no file, and the data structure's own name is taken as the external
file name:
DCL-DS empmast EXT QUALIFIED END-DS; // resolves the file EMPMAST
Adding EXTNAME names the file explicitly, and that name wins:
DCL-DS empRec EXT EXTNAME('EMPMAST') QUALIFIED END-DS;
EXTNAME may also be used without EXT - it implies the structure is
externally described. EXT combines with QUALIFIED, TEMPLATE, PREFIX,
ALIAS and INZ. The file is resolved from the --dds-path or the JDBC
catalog exactly as the fixed-format form resolves it; if neither is available at
compile time the compiler reports TRN1014.