The Data Model Resource Book, Volume 3: Universal Patterns for Data Modeling

Silverston c09.tex V2 - 11/21/2008 3:16am Page 482

482 Chapter 9 ■ Using the Patterns

What Are the Weaknesses of Using Patterns

for the Solution?

The weaknesses of applying patterns for requirements gathering and proto-

typing are as follows:

Using level 1 patterns does not generally provide a good basis for

implementations. Granted, in some very specific circumstances where

a set of data is very static and the values are not generally reused, you

may use a level 1 pattern solution for an implementation, but these situ-

ations are very rare indeed. Also, if level 1 patterns are implemented in

a database design, they would often cause redundant data. The level 1

patterns often include many attributes that are not normalized (that is,

they don’t follow 1

st

,2

nd

,or3

rd

normal form). For example, if you used

the Level 1 Classification Pattern to implement a customer size field

where the values are ‘‘Large,’’ ’’Medium,’’ and ‘‘Small,’’ this would lead

to many instances that redundantly had the value ‘‘Large,’’ as opposed

to having a foreign key that pointed to a CUSTOMER SIZE table, which

is how it would be modeled using the Level 2 Classification Pattern.

When level 2 patterns are used instead of Level 1 Patterns, you lose

some specific understanding. For example, we created STATUS TYPE

and CUSTOMER STATUS in Figure 9-2 to replace active from date and

active thru date that were attributes of CUSTOMER in Figure ...