When we consider the Data Warehouse approaches, there are primarily two approaches- Top-Down and Bottom-Up
The selected approach will deeply affect the Data Warehouse lifecycle.
Top-down (Inmon’s Approach)
In this approach, first the Data Warehouse is built which is mostly a normalized Data Model and thereafter Data Marts are fed from the Enterprise Data Warehouse. The DMs are specific to subject area or departments.
Advantages of This Approach:
The Enterprise Data Warehouse has the data from most or all departments of the Enterprise.
We will have integrated Data Warehouse. We can generate analytics for across the Subject Areas or Departments.
Disadvantages of This Approach:
- High initial cost.
- Integrating Master Data from all the departments would be challenging. It may lead to implementation of Master Data Management which itself is substantial undertaking.
- It will take significant to time to come up with a even small prototype of reporting; and business users may lose interest and trust.
- Long term implementation plan may be discouraging.
Bottom-Up (Kimball’s Approach)
In this approach, the Data Marts are created first, each specific to a particular subject area or department of the organization.
And as and when required, the Data Marts can combine into a larger Data Warehouse.
Kimball’s Data Warehouse architecture is also known as Data Warehouse bus (BUS).
Takes lesser time, shorter time for initial setup.
Which approach to choose?
It depends on the business objective of the organization, nature of business, time and cost.
Inmon’s approach is more suitable for stable businesses where business changes are not very often. With changes, they do not change the design instead they accommodate the changes in existing data model.
However, if the focus is on quick win, the Kimball’s approach is more suitable.
