When running FASTA, or other database-search programs, @MYTEST.FIL is given in place of a database name. This makes it very easy to manage a database. You need only keep a directory containing your personal sequences, and a list pointing to those sequences.
This is not sufficient for the STRINGSEARCH program, as any text in your personal data will not have been indexed. To do this, you must run DATASET which builds a whole database.