Yesterday I talked about the differences in dimensions versus facts. Today I’d like to extend that discussion with the importance of Conformed Dimensions.
One of the major advantages of a data warehouse is the ability to combine data from various, and sometimes vastly different, systems. Let’s take a common problem: your company has three different systems, sales, production, and purchasing. You’ve bought these from three different vendors, so unfortunately the part numbers used throughout the systems are not consistent, but you need to generate some reports showing how part x went into product y and was sold to customer z.
Unfortunately the part numbers are not consistent across the three systems because, as I mentioned, they came from three different vendors. What’s a programmer to do?
This is where conformed dimensions come in handy. In the part dimension table you create a surrogate key. This is the new primary key for a part, which is simply a made up value. Maybe you chose to use a GUID, or perhaps it’s just an auto incrementing integer. Regardless, this is now your new “part number” for all 3 systems once you bring the data in the warehouse.
You would add three more fields to the part dimension table. In addition to the primary key you would have a field “saleskey”, a field “productionkey”, and finally a “purchasingkey”. Then, when bringing your sales data into the warehouse, you look up the saleskey in the dimension table, get the primary key for the part, and place it in the fact sales table.
Repeat with production and purchasing systems. By now you are beginning to get the idea. Because you have conformed the part key across the three fact tables, you can now draw reports using the new part key as a common thread to join the various fact tables together.
This process is known as a conformed dimension. ALL of your dimensions in your warehouse need to be conformed if you want to truly leverage the power of your warehouse. Employees, parts, customers, and locations are just a few examples of dimensions you’d want to conform.
As you can see, having conformed dimensions is key to the success of your warehouse. Failure to conform your dimensions means you loose one of the most powerful features of warehousing, the ability to produce reports across differing systems.