12.4. Non-primitive Data Type Classes

The type of an attribute may be expressed as a non-primitive class in its own right in a domain model. For example, in the POS system there is an item identifier. It is typically viewed as just a number. So should it be represented as a non-primitive class? Apply this guideline:

Represent what may initially be considered a primitive data type (such as a number or string) as a non-primitive class if:

  • It is composed of separate sections.

    • phone number, name of person

  • There are operations usually associated with it, such as parsing or validation.

    • social security number

  • It has other attributes.

    • promotional price could have a start (effective) date and end date

  • It is a quantity with a unit.

    • payment amount has a unit ...

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