Design Patterns Elements of Reusable Object-Oriented Design

What is Good Design?  30 years ago, Christopher Alexander (an architect currently at UC Berkeley) asked: – Are beauty and quality objective? » Can we agree some things are beautiful and some are not? – What makes a good architectural design? – What makes bad architectural design? – Can we recognize good design? – Is there an objective basis for such a judgment? – Is there a basis for describing common consensus  Alexander believed that beauty can be described through an objective basis that can be measured  Examples: – Symmetry is good –Use half-round arches to support bridges and in doors  Equivalent ideas exist in software design CS@CSULB 3 Patterns  Alexander looked at different structures that solved the same problem  Found similarities between designs of high quality  Alexander called these similarities patterns  A pattern is a solution to a problem in a context