Developer.com: PHP Pattern Principles

“Although design patterns simply describe solutions to problems,
they tend to emphasize solutions that promote reusability and
flexibility. To achieve this, they manifest some key
object-oriented design principles.

“This article will cover

• “Composition: How to use object aggregation to achieve greater
  flexibility than you could with inheritance alone
• “Decoupling: How to reduce dependency between elements in a
  system
• “The power of the interface: Patterns and polymorphism…”

Complete
Story