Ideally, you must start the design of your ETL system with one of the toughest challenges: surrounding the requirements. By this we mean gathering in one place all the known requirements, realities, and constraints affecting the ETL system. We'll refer to this list as the requirements, for brevity.
The requirements are mostly things you must live with and adapt your system to. Within the framework of your requirements, you will have many places where you can make your own decisions, exercise your judgment, and leverage your creativity, but the requirements are just what they are named. They are required. The first section of this chapter is intended to remind you of the relevant categories of requirements and give you a sense of how important the requirements will be as you develop your ETL system.
Following the requirements, we identify a number of architectural decisions you need to make at the beginning of ... read full excerpt from The Data WarehouseETL Toolkit: Practical Techniques for Extracting, Cleaning, Conforming, and Delivering Data ebook
