Indent
Provide an Interface for creating families or related or dependent objects without specifying their concrete classes.

Applicability
• a system should be independent of how its products are created, composed, and represented.
• a system should be configured with one of multiple families of products.
• a family of related product objects is designed to be used together, and you need to enforce this constraint.
• you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations.
Structure