Thorsten have point us that for his task it is not comfortable when command
LINK RECORD (1) OF T1 TO RECORDS(3, 7, 9) OF T2
throws error and stops, if link 1-7 already exists.
We have agree and improve these commands adding suffix
LINK … [IF NOT EXISTS]
UNLINK … [IF EXISTS]
This suffix is similar to CREATE/DROP commands. If it is specified, then error is not fired and command continue work for other pairs of links.