Log file that stores a record of changes to a 4D database (.4DD) file; saved along with the database file and uses a similar filename; designed to keep track the updates made to the database.

Multiple 4DL files are often saved along with a 4DD file. For example, a database named "db1.4dd" may generate an initial log file named "db1[0001-0000].4dl." If the database has bee saved 5 times, the program will generate a log file named "db1[0005-0000]." If the log file itself is then saved 3 times, it will be named "db1[0005-0003].4dl."