The DELETE statement has the form
DELETE device:index
and removes a record from an ISAM type file only. No attempt is to remove records from associated files, as they may be referenced from other files as well. (Changing data with INSERT and STORE works differently, as in all your dealings with Mr. Smith you will want his latest address.)
Thus, it may be used with indexed non-database files.
Records cannot be deleted within sequential files; use STORE to blank a record within a direct-access file.