I’ve been reading “Managing the Design Factory” by Donald Reinertsen.  There is an interesting observation he makes.  In manufacturing, you know all of your requirements up front.  Whereas, when you are doing design, you know very little up front with most of the requirements being known about a third of the way through.  Don’t get hung up on exactly when you know – as long as you agree that in designing a product, you don’t know it all up front.

Comparing Two Patterns: Adapter and Façade

(Note: if you are unfamiliar with these patterns, you can read about them at our pattern repository)

One reason people often struggle to understand how to get real value from patterns is that sometimes two or more of them can look, at first glance, extremely similar. When I'm teaching patterns, people will very often point out how similar the Strategy and Bridge patterns are, or the Decorator and Chain of Responsibility, or the Factory Method and Abstract Factory, etc…

Usually this is because people often confuse the example of the pattern that's being presented to them with the pattern itself. Patterns are neither UML diagrams nor code examples; they are a higher concept that captures best practices, domain and implementation forces, and the consequences (both benefits and costs) of certain decisions. Diagrams and code are simply representations of the patterns, and are always more specific and narrow than the patterns themselves are.

This misunderstanding is an opportunity, however, because when we compare two patterns that appear similar and determine how they are actually different, we can sometimes dramatically enrich our understanding of them.