What This Book Is About

Simply put, this book is about building model-driven Web applications. It is not a book on how to use a particular tool, a step-by-step recipe, or new methodology. It is simply a guide for the project manager, architect, analyst/designer, and implementer of Web applicationsanyone who wants to build robust, scalable, and feature-rich Web applications using the proven object-oriented techniques that traditional client/server applications have been built with for years now. This book builds on the techniques of object-oriented application development rather than defining its own. I say model-driven because the models are the fundamental driving factor in the evolution of the system's development artifacts.

Most of the ideas expressed in this book are not original, and for good reason. Many of the concepts and methods described in this book have developed and evolved over years of practice in multiple domains. These object-oriented practices have enabled projects to be delivered on time and on budget and, most important, have made them predictable. For the most part, the object-oriented principles described in this book are based on the collective works of Grady Booch, Jim Rumbaugh, and Ivar Jacobson, who are also known as the "three amigos."

The amigos are the principal creators of the Unified Modeling Language (UML), a notation for visually expressing the models of software-intensive systems. For many, UML also represents a method, although technically this is incorrect. UML is just a language but like any language expresses things with certain biases. In particular, UML expresses system models and designs in an object-oriented fashion, even though it is being used to express system types as varied as generic business organizational structures and processes to real-time embedded system designs.

The term UML is included in this book's title because it is at the heart of all the discussions of building Web applications in this book. Most of the original work in this text is in the Web Application Extension for UML (WAE). In it, the UML notation is extended with additional semantics and constraints to permit the modeling of Web-specific architectural elements as a part of the system's model. A major theme in this book is that it is critical to model all of a system's business logic, regardless of where or how it is being implemented in the system. For Web applications, this means that in our UML models, we need to capture the execution of business logic in Web pages, in client-side scripts, and in Web components. By having a single central model of all the business logic in a system, we are better able to understand it and eventually to elaborate on it in future releases of the system.

The first edition of this book was for the most part written before I joined Rational Software Corporation. At the time, I was an independent consultant specializing in Web applications. The ideas expressed in the first edition of the book were not, of course, supported by any vendor's tool. Rational Rose was and is my modeling tool of choice; with its extensibility interface, I managed to get some specialized icons in the tool and even create some scripts that would forward engineer ASP components from class diagrams. I am proud to say that since then, the Rose development team has included round-trip engineering of both ASP and JSP components.

Full support of the WAE specification is not, however, in the current version of the product; nor will it ever be. Some things simply are not appropriate for round-trip engineering. They may not be suitable for automation, but they are still important to model since the real goal of modeling is understanding and comprehension, not automation. This book lays out the entire specification with some recommendations on what is important and what is not. But in the end, it will be up to you and your team to decide how much detail you'll need in your models.

Because this is a book about building model-driven Web applications, it focuses on three key topics. Modeling, process, and Web architectures are discussed in the remainder of this chapter.