Mark Whitehorn explains about ETL: Extract, Transform, and Load. He also explains how important is ETL to you and how important is ETL to all the companies? It's really important, because as you extract, transform, and load data into your data warehouse, it's then going to be used for a variety of other things. You are going to use it for data mining. You are going to use it for LAN. You can use it for reporting. If your ETL isn't efficient, then all of those processes suffer.