You have learned that you can keep an audit trail to track observation updates made to an individual data set in place. However, if you replace the data set, the audit trail is lost. Generation data sets enable you to maintain multiple versions or generations of a SAS data set. A new generation is created each time the file is replaced.

By default, generation data sets are not in effect. As the SAS data set A is replaced, there are two copies of A in the SAS library. When the DATA step completes execution, SAS removes the original copy of the data set A from the library.

When generation data sets are in effect and the SAS data set A is replaced, there are two copies of A in the SAS library. When the DATA step completes execution, SAS keeps the original copy of the SAS data set A in the library and renames it.

Each generation of a generation data set is stored as part of a generation group. Each generation data set in a generation group has the same root member name, but each has a different version number. The most recent version is called the base version. When generations are in effect, SAS filenames are limited to 28 characters. The last four characters are reserved for the version numbers.