Databases Reference
In-Depth Information
areas in data warehousing. A data warehouse is not merely a collection of
subject areas. The subject areas must be able to work as a cohesive whole
within the data warehouse. But what are the symptoms that occur when a
data warehouse is not quite a victim of its own success, a data warehouse
that lacks focus and direction, that lacks a purpose? Three key indicators
of a data warehouse provide a good clue as to the success or failure of a
data warehouse. Those three key indicators are performance, relational
integrity, and data quality.
Performance
The first clue that a data warehouse is not quite a success is the inability to
return a result set. This may seem obvious. It should be obvious. Maybe
that is why it is the first clue…because it is so obvious. When users run
a report or a query and…and…and…and…they eventually go home for
the night, performance is definitely an issue. My first data warehouse was
described as “a rock” for its ability to remain motionless and yield abso-
lutely nothing, including data. Performance was an issue.
When a data warehouse is unable to yield data the root cause can be
many things. But the first root cause is a lack of purpose. A data ware-
house that is built to look like a data warehouse will do exactly that: it will
look like a data warehouse. But a data warehouse that is built to render a
Sales report will do exactly that: it will render a Sales report. Why is that?
If from the first planning meeting everyone understood that, regardless of
what may or may not be in the data warehouse, it must be able to generate
a Prior Day Sales report, then everyone will begin thinking of the data
in terms of the Prior Day Sales report. First, the Sales subject area will be
included. Second, Sales will be grained by the day, and maybe by other
time grains. Third, the dimensional properties and attributes necessary
to describe, quantify, and qualify data in the Prior Day Sales report will
be included. In short, everything necessary to make the Prior Day Sales
report a success will be included and optimized so that when the manag-
ers who decided to fund the data warehouse because they want their Prior
Day Sales report ask for this report, that's exactly what they will get.
What was the purpose of the first subject area of that data warehouse?
The purpose was the Prior Day Sales report. Now comes the fun part.
When you hit the bull's-eye right in the center, what is within three inches
in every direction? The answer is…more bull's-eye. By virtue of having a
purpose (deliver the Prior Day Sales report) the data warehouse is able to
