Let's see . . . disadvantages . . . hmmm. scorn of anyone that understands
data warehousing? On your resume putting "created a completely normalized
DW" and wondering why everyone giggles when they read it.
Actually, a normalized schema will probably use less space than
denormalized.
The key point is your users. A typical normalized design means a lot of
tables. These tables must be joined in specific manners. Non-I.S. users find
this intimidating. So they don't use it. So you've spent a lot of time
creating a DW only to have nobody use it.
Normalized schemas are optimized for inserts and updates, not
generating reports. To generate a report from an OLTP normalized schema, you
usually start by interviewing the developers. And they usually have to do
some research. A DW is a "write mostly" schema. Our DW is only refreshed
weekly. Sunday is spent loading it and Monday the users charge in and run
reports all day.
Study star schema. Go to http://www.ralphkimball.com and read
articles he has written, starting with the oldest ones and working forward.
Read Ralph Kimball's book "The Data Warehouse Toolkit: Practical Techniques
for Building Dimensional Data Warehouses". Classic work, excellent starting
point.
A beginning star schema DW should have only a central fact table and
4-6 dimension tables. Non-computer-geeks actually have a hope of
understanding how to navigate that. How many tables did your 3nf schema
produce?
Or go ahead, build a normalized one, then study and build the second
version incorporating the hard-won lessons others have learned.
Dennis Williams
DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----Original Message-----
Sent: Friday, May 10, 2002 1:43 PM
To: Multiple recipients of list ORACLE-L
- that is the question
Hi.
We are designing a small database using a data
warehousing desing. We have created a 3rd normal form
and are now debating whether and how to denormalize
it. I see the pluses of denormalization - easier
queries creation and tuning. What are the
disadvantages that we should be aware of? Wasted space
is not an issue because the tables a pretty small.
What else should we consider as a potential issue?
thank you
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