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Purpose and Scope

by Derek Hatley, Peter Hruschka, and Imtiaz Pirbhai

Adapted from Process for System Architecture and Requirements Engineering. Reprinted by permission. All rights reserved. See below for copyright notice.

The overall purpose of Process for System Architecture and Requirements Engineering is to present a broad approach to the effective development of systems, especially those involving multiple disciplines—as most systems do. We use a variety of practical, real-world case studies to illustrate the nature of systems and the system development process, and we include system models that can be used in the process.

Updated Methods

The book builds on the methods and techniques originally described in Strategies for Real-Time System Specification [Dorset House, ISBN: 0-932633-11-0, 1988]. It is based on more than a decade of experience, our own and many others', in the practical application and teaching of the methods and techniques. When Strategies was written, we were working in the avionics engineering field, but since then, we have helped to introduce the methods, and have taught and facilitated their use, on a wide variety of projects, ranging from communications systems to biomedical systems, and from three-person projects to those of a hundred people and more.

The wide acceptance of the methods—which became known as the Hatley/Pirbhai methods—has been gratifying, but not all practitioners have used them correctly or effectively. There have been several changes over the years in the methods and their use, and several CASE (computer-aided system/software engineering) tool developers have sought to automate the methods. Besides a few notable exceptions, most of these tools have fallen far short of doing the job adequately. Our goal, then, is to share the benefit of our experiences, good and bad, in the hope of improving the overall state of system development and the methods and tools that support it.

System Development Process

An important feature of our approach is that it applies equally well to all technologies, and thereby provides a common language for developers in widely differing disciplines. Another important feature is the coexistence of the requirements and architecture methods, and of the corresponding models they produce. Our approach keeps these two models separate, yet it fully records their ongoing and changing interrelationships. This feature is missing from virtually all other system and software development methods, and from most CASE tools, because most of them automate only the requirements model. We are not alone in our focus on the system development process: It is also the focus of a great deal of work throughout the industry.

What's in a Name?

When we wrote Strategies, we did not formally introduce a name for the methods it describes. Practitioners eventually referred to them as the "Hatley/Pirbhai methods," or simply the "H/P methods." This presents us with a dilemma: First, many more people than the two original authors have now contributed to the methods, and at the very least the name should include that of the third author, Peter Hruschka; second, the methods themselves do not represent the entirety of Strategies, and they represent even less the entirety of this book. What we describe in both books is a process for which the methods provide support. Our solution to this dilemma is to formally adopt separate names for the methods and for the process. Accepting the reality that the industry has de facto adopted a name for the methods, we propose changing that name to the "Hatley/Hruschka/Pirbhai" or "H/H/P" methods. For the process, the title of this book is about as good a description as we can think of: Process for System Architecture and Requirements Engineering. Its one flaw is its length, so we propose to use its acronym: PSARE, pronounced sari, as in the traditional southern Asian garment.

Audience and Structure

The intended audience for this book includes system managers, system architects, system engineers, and managers and engineers in all of the diverse engineering technologies, such as mechanical, electrical, electronic, hydraulic, chemical, manufacturing, computer hardware, and computer software. This book may also be used as a text for graduate courses in system engineering. It is intentional that no exercises are included: Practical examples from the students' own experiences are much better than "canned" exercises in a book. However, the case studies in Parts I and II can serve as exercises for students to study, critique, extend, and modify.

There are two main parts in this book, and an important appendix:

  • Part I: Concepts: An introduction to the system approach, to system models, to the system development process, and to the application of the models to the process. A hospital monitoring system is used as an illustrative case study.

  • Part II: Case Study-Groundwater Analysis System: An in-depth look at the development of a highly multidisciplinary system.

  • Appendix: Summarizes changes, improvements, and misconceptions regarding the methods and their use since Strategies for Real-Time System Specification was written. This appendix should be particularly helpful to those who have already used the methods, and need a quick update on what is different about them in this book.

A Participative Case Study on the Web

While we were writing this book, software development went through some radical changes. In response, we decided to move the book's third case study to the Web. This case study is of an automated airline quick-ticketing system (QTS) that is user-interface driven and very software-intensive. We consider the Web to be the right medium for this case study because the UML and other software notations are still changing, with new versions almost every year. The Website is www.psare.com, and it will include a forum where those interested can discuss issues, the methods, the QTS, and other systems and models as we develop them.

A Caveat

Our commitment should be to developing quality systems that will satisfy the customers' needs. Very often, that end goal is missed. Methods and automated tools are only vehicles to reach that goal. Automated tools automate methods; the methods precede their automation. Our commitment should be first to the process of satisfying customer needs, then to the methods that facilitate that process, and finally to the tools that automate the selected methods. Even though we use automated tools to present our case studies, please remember

Methods and automated tools are of no use without properly qualified people who are using a well-defined development process, and who are dedicated to satisfying customer needs.

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COPYRIGHT NOTICE: This excerpt from Process for System Architecture and Requirements Engineering [ISBN:0-932633-41-2] appears by permission of Dorset House Publishing. Copyright © 2000 by Derek J. Hatley, Peter Hruschka, and Shams Pirbhai. All rights reserved. See http://www.dorsethouse.com/books/psare.html. The material contained in this file may be shared for noncommercial purposes only, nonexclusively, provided that this Copyright Notice always appears with it. This material may not be combined with advertisements, online or in print, without explicit permission from Dorset House Publishing. For copies of the printed book or for permissions, contact Dorset House Publishing, 1-800-342-6657, 212-620-4053, http://www.dorsethouse.com, info@dorsethouse.com, New: 3143 Broadway, Suite 2B, New York, NY 10027 USA. Additional rights limitations apply, as presented in the Legal Disclaimer posted at http://www.dorsethouse.com/legal.html.



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