Working with backup sets : Microsoft SQL Server database backup sets (Windows)
 
Microsoft SQL Server database backup sets (Windows)
About Microsoft SQL Server database backup sets
The following sections provide information about Microsoft SQL Server database backup sets.
The Microsoft SQL Server backup set type always performs a full database dump of the Microsoft SQL Server. After the initial backup of a SQL database, the subsequent backups send incremental forever.
DS-Client does not support a separate backup of a database’s transaction log. If you want to back up the transaction log, you must back up the corresponding database with the Backup Transaction Log backup item option selected.
The value of separate transaction logs is that they can be restored as separate dump files (to alternate location). This method is better than restoring from a full backup only if there is a specific transaction point you want to restore to (between two full backup sessions).