What's New in the Second Edition

Our goals for this second edition are the same as they were for the first, but the passage of time since the writing of the first edition has brought new developments in the field and new understanding of the important underpinnings of software architecture. We reflect the new developments with new case studies and our new understanding both through new chapters and through strengthening the existing chapters. Also, the writing of this second edition has been strongly influenced by several other books that we have collectively authored since the publication of the first edition-Documenting Software Architectures, Evaluating Software Architectures: Methods and Case Studies, and Software Product Lines: Principles and Practice. The creation of these books, along with other technical and research activities, has greatly influnced us in developing this book. This second edition reflects the fact that architecture analysis, design, reconstruction, and documentation have all had major developments since the first edition.

Architecture analysis has developed into a mature field with industrial-strength methods-reflected here by a new chapter in Part Three about the Architecture Tradeoff Analysis Method (ATAM^SM). Many industrial organizations have adopted the ATAM as a technique for evaluating software architectures.

Architecture design has also had major developments since the first edition. The capturing of quality requirements, their achievement through small-scale and large-scale architectural approaches (tactics and patterns, respectively), and a design method that reflects knowledge of how to achieve them are all discussed in various chapters. Three new chapters treat understanding quality requirements, achieving qualities, and the Attribute Driven Design Method (ADD).

Architecture reconstruction, or reverse engineering, is an essential activity for capturing undocumented architectures. It can be used as a portion of a design project or as an analysis project, or as input into a decision regarding what to use as a basis for reconstructing a system. In the first edition, we briefly mentioned a tool set (Dali) and its uses in the re-engineering context, but in this edition the topic merits its own chapter.

Documenting software architectures is another topic that has matured considerably in the recent past. When the first edition was published, the Unified Modeling Language (UML) was just arriving on the scene. Now it is firmly entrenched, a reality reflected here with all-new diagrams. More important, an understanding of the kind of information to capture about an architecture, beyond which notation to use, has emerged. A new chapter covers architecture documentation.

The application of software architecture to enable organizations to efficiently produce a variety of systems based on a single architecture is summarized in a totally rewritten chapter on software product lines. This chapter reinforces the link between architecture and an organization's business goals, in view of the fact that product lines (based around a software architecture) can enable order-of-magnitude improvements in cost, quality, and time-to-market.

In addition to the architectural developments, the technology for constructing distributed and Web-based systems has become prominent in today's economy. We reflect this trend in our updated chapter on the World Wide Web by using Web-based examples in the chapter on the ATAM and the chapter on building systems from components, by replacing the case study on Common Object Request Broker Architecture (CORBA) with one on Enterprise JavaBeans (EJBs), and by introducing a case study on a wireless EJB system designed to support wearable computers for maintenance technicians.

Finally, we have added a chapter that looks more closely at the financial aspects of architectures. In this chapter, we introduce a method-the Cost Benefit Analysis Method (CBAM)-for basing architectural decisions on economic criteria, in addition to the technical criteria that we discussed previously.

As in the first edition, we use the Architecture Business Cycle (ABC) as a unifying motif. All of the case studies are described in terms of the quality goals that motivated the system's design and how the system's architecture achieves those goals.

In writing the second edition, as with the first, we were very aware that our primary audience is practitioners, and so we have focused on material that has been found useful in many industrial applications as well as what we expect practice to be in the near future.

We hope that you enjoy reading this second edition at least as much as we enjoyed writing it.