DATA WAREHOUSING FUNDAMENTALS: A Comprehensive Guide for IT Professionals

2.3. DATA WAREHOUSES AND DATA MARTS

If you have been following the literature on data warehouses for the past few years, you would, no doubt, have come across the terms "data warehouse" and "data mart." Many who are new to this paradigm are confused about these terms. Some authors and vendors use the two terms synonymously. Some make distinctions that are not clear enough. At this point, it would be worthwhile for us to examine these two terms and take our position.

Writing in a leading trade magazine in 1998, Bill Inmon stated, "The single most important issue facing the IT manager this year is whether to build the data warehouse first or the data mart first." This statement is true even today. Let us examine this statement and take a stand.

Figure 2-4. Data granularity.

Before deciding to build a data warehouse for your organization, you need to ask the following basic and fundamental questions and address the relevant issues:

• Top-down or bottom-up approach?

• Enterprise-wide or departmental?

• Which first—data warehouse or data mart?

• Build pilot or go with a full-fledged implementation?

• Dependent or independent data marts?

These are critical issues requiring careful examination and planning.

Should you look at the big picture of your organization, take a top-down approach, and build a mammoth data warehouse? Or, should you adopt a bottom-up approach, look at the individual local and ...