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

Silverston c09.tex V2 - 11/21/2008 3:16am Page 528

528 Chapter 9 ■ Using the Patterns

obvious to the business or the application development team. The data model

patterns can help develop star schemas in the following ways:

Patterns may be used to develop an initial data model before the star

schema design in order to show how various types of common data

may be modeled. Allowing the data modeler to pick from various pat-

terns and incorporate the appropriate amount of flexibility in the data

model provides clues regarding an effective structure for the dimen-

sions. For example, if there is a strict hierarchy where a product is within

a product line, which is within a product family, it may be more suited

to put them in as levels (‘levels’ is used here as a star schema term)

within the same dimension. If products may be in multiple categories

and they don’t roll up neatly in a hierarchical fashion, it is still possi-

ble to put them in the same dimension; however, it may be more clear

to have separate dimensions for PRODUCT and PRODUCT

CATEGORY because there is a many-to-many relationship between

them.

We can get hints about how to structure dimensions from the patterns.

Dimensions tend to usually resemble level 1 patterns and sometimes

level 2 patterns (for example, when we showed the customer status

pattern). The complexity that resides in a logical data model is often

‘flattened out’ in order to ...