Beginning Database Design Solutions by Rod Stephens

Author:Rod Stephens
Language: eng
Format: epub, pdf
Publisher: John Wiley & Sons
Published: 2010-12-27T16:00:00+00:00

Again, you don't need to use psychic powers to build all of the features that the customer will need in the next 15 years, but keep your eyes open during requirements gathering and try not to close off opportunities for later change.

Too Much Normalization

Taken to extremes, too much normalization can lead to a database that scatters related data all over the place for little additional benefit. It can make the design confusing and can slow performance.

When you normalize, think about what a change will cost and what benefits it will provide. Think about how the data will be accessed. If data is only read and written through stored procedures or middle-tier code, that code can help play a role in keeping the data consistent and may allow you to get away with slightly less normalization in the database's tables. Putting every table in Fifth Normal Form or Domain/Key Normal Form isn't always necessary to keep the data safe.

I once worked on a project where a certain database developer (who coincidentally had just taken a class in database normalization) wanted to split every data value out into a separate table. For example, a customer record would contain little more than a CustomerId. Then a Values table would hold the actual data in its three fields Id, ValueName, and ValueData. To look up a customer's name, you would search the Values table for a record with Id equal to the customer's ID and ValueName equal to “Name.” In some bizarre otherworldly sense, this table is very normalized and it lets you do some amazing things. For example, you could decide to add a new EarSize field to the customer data without changing the tables at all. However, that design doesn't reflect the structure of the data so it would be next to impossible to use.

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