Software patterns have revolutionized the way practitioners and developers think about the way software is designed, built and documented. International authors explain what pattern languages are, what they are not, and how to use them effectively. POSA 4 addresses the question of what a pattern language is and compares various patterns paradigms. Practitioners, developers and programmers operating in an object-oriented environment will find this book to be an invaluable resource. The material covers some concepts, a story and the language.