Good software developers often adopt one or several architectural patterns as strategies for system organization. But, although they use these patterns purposefully, they often use them informally and nearly unconsciously. This book organizes this substantial emerging "folklore" of system design -- with its rich language of system description -- and closes the gap between the useful abstractions (constructs and patterns) of system design and the current models, notations and tools. It identifies useful patterns clearly, gives examples, compares them, and evaluates their utility in various settings -- allowing readers to develop a repertoire of useful techniques that goes beyond the single-minded current fads. Examines the ways in which architectural issues can impact software design; shows how to design new systems in principled ways using well-understood architectural paradigms; emphasizes informal descriptions, touching lightly on formal notations and specifications, and the tools that support them; explains how to understand and evaluate the design of existing software systems from an architectural perspective; and presents concrete examples of actual system architectures that can serve as models for new designs. For professional software developers looking for new ideas about system organization.