Gianluca Sartori (5/8/2009)
Exactly: the transaction log backup is taken from the last backup, either full or tlog.
Log backups contain the log records since the previous log backup. Full and diff backups do not truncate the transaction log. The only time a log backup will contain log records since a full, is if that's the first log backup done after setting the DB into full/bulk logged recovery.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability