Abstract :
Early in the history of programming, brilliant people realized that every good software system has some desirable properties: It should be extensible; parts of it should be modifiable without major impact on other parts; and so on. Because of the Feigenbaum Bottleneck, it is very hard to describe precise, step-by-step instructions to build systems with such properties. It is easier to articulate the desirable properties in the form of design principles. Over the years, the wealth of knowledge accumulated as design principles has reached a critical mass. Entire books are now dedicated to the subject. Still, despite this body of knowledge, design remains difficult. A major problem is that principles are ambiguous and not very constructive. In more recent times, design patterns have emerged as a valid alternative to the principles-driven approach. If principles represent the “say-what” approach to design, patterns are the “show-how” way
