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Re: Normalization

From: david wendelken <davewendelken_at_earthlink.net>
Date: Thu, 29 Jul 2004 09:32:10 -0700 (PDT)
Message-ID: <1550338.1091118730671.JavaMail.root@misspiggy.psp.pas.earthlink.net>

"Q: What are the basic guidelines one should keep in mind while
designing a database? Is denormalization always good?

  1. I used to teach database design in graduate school, and your question is excellent! The main purpose of high normalization was the reduction of disk space, back when it mattered in the 1970s."

I'm not so sure about that.

To me, the main reason for normalization is to properly think through PRECI= SELY and ACCURATELY what I need to model. The secondary reason was to prev= ent discrepancies between "duplicated" data items. Tertiary to all of that was disk space. But then I started in the '80s, wh= en disk space was becoming much cheaper.

"Today, I always introduce redundancy into the model whenever it can
eliminate an SQL join, but not always. I make my decision based on two criteria:

1 =96 The size of the redundant item

2 =96 The volatility of the item (e.g. how often do I need to duplicate updates)"

I introduce redundancy when it can eliminate lots of joins lots of times, o= r dramatically speed up a critical process. And, yes, I balance that against the cost of making sure that the redundant=  data stays synchronized and the database sizing implications.

But doing it to just to avoid an occasional join? No way!



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Received on Thu Jul 29 2004 - 11:28:47 CDT

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