Managing Software Requirements: A Unified Approach (The Addison-Wesley Object Technology Series)
Context and AcknowledgmentsThe knowledge delivered in this book represents the cumulative experience of a number of individuals who have spent their careers defining, developing, and delivering world-class software systems. This book is not an academic treatment of requirements management. During the 1980s, Don Widrig and I were executives in a small company producing software solutions for customers. When we developed many of the requirements management practices described in this book, our perspective was of those accountable for both the outcomes of the software systems we developed and the results that had to be delivered to shareholders. As the performance of the delivered software was critical to the success of the business venture itself, we tended to discourage petty biases, personal preferences, and experimentation with unproven techniques.Over the past decade, the techniques have evolved and have been enhanced by new experiences, extended with the help of additional expertise, in different companies and in different circumstances. But all of the techniques presented are "real-world" proven and have withstood the test of time. Perhaps even more important, they have withstood the technological change that has occurred in the industry during this period. Indeed, most of the principles in this book are independent of changing trends in software technology. We can therefore at least hope that the knowledge expressed herein can deliver some lasting value.Requirements Lessons from Building Software for OthersAt first, I just hated computers. ("What? I stayed here all night and I have to submit this batch job again because I left out a 'space'? Are you crazy? Let me in that room....") My first "real computer" was a minicomputer, which, although incredibly limited in performance by today's standards, was unique in that I could touch it, program it, and make it do what I wanted. It was mine.My early research applied the computer to analyze physiological signals from the human body, primarily EKGs, and the dedicated computer was a wonderful tool for this job. Out of this experience, I began to apply my programming skills and experience with real time software systems to the needs of the industry.Eventually, I incorporated RELA, Inc., and began a long, and perhaps unusually difficult, career as CEO of a contract software development business. My coauthor, Don Widrig, joined me at RELA in the early years as Vice President of Research and Development. He had the primary accountability for the success of the many systems that we developed.Over the years, the company grew rapidly. Today, the company employs many hundreds of people and has diversified beyond providing just software to providing complete medical devices and systems that encompass software, as well as mechanical, electronic, optical, and fluidics-handling subsystems. However, at the heart of each and every machine, including the latest DNA fingerprinting in vitro diagnostic clinical laboratory, lies one or more computers, reliably and routinely delivering its steady heartbeat through the rhythm of a real-time multitasking system.Initially, we would program anything for anybody, from antenna positioning software to such games as laser tag, automated guided vehicles for amusement parks, educational products, welding robots, and automated machine controls. We even developed a large distributed computer system that auto-matically detected and counted the presence of commercials on television. (Our motto then was "We make computers to watch commercials so you don't have to!") Perhaps the only thing the software we developed was that we developed it for others--we were not domain experts in the field, and we couldn't cover our own paychecks if we had to. We were completely dependent on the cus-tomer's satisfaction as the final determination of outcome. In many ways, such an environment was very conducive to effective requirements management. Here's why:We knew little about the domain, so we were dependent on customers for the requirements. There was little temptation to simply make them up; we had to ask, and we had to learn how to ask the right questions the right way, at the right time.   Our customers often knew little about computers, so they were dependent on us to translate their needs and wishes into technical requirements.   The fact that money changed hands created a rigorous interface between the developer and the customer.   Quality was easy to measure: We either got paid or didn't.It was in this environment that we discovered the first of two fundamental questions that face software developers on each and every project. This question dominated our behavior for many years and remains today as perhaps the toughest question to answer in any software project. And the Big Question is:Big Question 1: "Exactly what is this software supposed to do?"The principles and techniques presented in Team Skill 1, Analyzing, the Problem; Team Skill 2, Understanding User Needs; and Team Skill 3, Defining the System, were developed over more than a decade as a means to discover the answer to this question. Each of these techniques has proved its worth and has demonstrated its effectiveness in many real-world projects. It was also during this period that I first became aware of the work of Donald Gause, and Jerry Weinberg especially their book Exploring Requirements: Quality Before Design, (1989). Because their book heavily influenced our work, we have borrowed a few key concepts from it for this book, both because the concepts work and because we thought it only fair that you share the Gause and Weinberg experience.Lessons from Building High Assurance SystemsOver time, RELA began to specialize in the development of various types of computer-based medical devices and systems: portable ventilators (breathing machines), infusion pumps, pacemaker programmers, clinical diagnostic systems, blood pumps, patient-monitoring equipment, and a plethora of other diagnostic and therapeutic devices.It was early during the ventilator development project that the ultimate accountability for what we were doing really hit us: Whoa, if we screw this up, somebody could die! Our primary concern was for the patient and for the family of the patient who was tethered to the device, a device on which we were executing some of the earliest, most time-critical, resource-limited software the world had yet seen. (Imagine the challenge of alpha and beta testing. You go first!)Clearly, this high-stakes endeavor caused us to take software very seriously at a fairly early time in the evolution of the embedded-systems industry. It became clear very quickly that sustainable success would require a combination ofA pragmatic process for defining and managing the requirements for the software   A solid methodology for the design and development of software   The application of various proven, innovative, techniques for verifying and validating that the software was safe and effective, and   Extraordinary skills and commitment on the part of both the software development and software quality assurance teams.I strongly believed at that time, and I am even more convinced today, that all of those elements are required to deliver any reasonably reliable software system of any significant scope. At RELA, Inc., this was to be the only way we could possibly ensure each patient's safety, the very survival of our company, and the economic futures of the employees and their families who depended on the company.Given our earlier success in the development and application of the various techniques we used to answer Big Question 1, we now moved on to the second fundamental question facing software development teams worldwide. Big Question 2 isBig Question 2: "How, exactly, will we know when the software does exactly that and nothing else?"The techniques we used to answer this question form the basis of Team Skill 5, Refining the System Definition, and Team Skill 6, Building the Right System.So, you can be confident that the techniques presented in this book are road hardened and well proven. Also, even if you are not in the business of developing safety-critical systems, you can rest assured that what follows is useful, practical, and cost-effective advice that you can use to develop software systems of the highest quality.   Although the techniques that we borrowed, modified, developed and applied at RELA, Inc., to address the two big questions were highly effective, I must also admit to one nagging uncertainty that kept me awake during the most serious crunch times on these projects:   "Given the highly manual nature of the requirements process, how long would it be before we made a single, but potentially dangerous, mistake?"   And there was also the matter of cost, as manual verification and validation were expensive and error prone. During this period, the discipline of mechanical engineering had advanced from a mechanical drawing arm to 3-D computer-aided design systems. In the same period, our software advances were limited, for all practical purposes, to having increased the level of abstraction in our programming languages: a good thing, for certain, but defect rates, lines-of-code productivity factors, and quality measures were relatively constant. Our experiments with the CASE tools of that period were met with mixed results. Frankly, as a software engineer and entrepreneur, I found the state of the art in "software engineering" to be embarrassing.   Although it was obvious that automation would never eliminate the critical- thinking skills required in software development, I did become convinced that automating some of the manual, record-keeping, and change management aspects of the process would free scarce resources to focus on higher, value-added activities. And, of course, we anticipated that development costs would be lower while reliability would be increased!   Lessons from the Requirements Management BusinessSo, in 1993, REQUISITE, Inc., was born, and a number of us committed to a course of action to develop and to market an innovative requirements management tool: RequisitePro. As we were continuously helping customers address their requirements management challenges during this time, much additional material for this book was born. We owe much of this work to those customers, and the customers at RELA, who essentially taught us everything we know on the subject.This portion of my career was heavily influenced by Dr. Alan Davis, who was Editor in Chief of IEEE Software magazine and held the El Pomar Endowed Chair of Software Engineering at the University of Colorado in Colorado Springs. Al joined the company as a director and advisor early on and was instrumental in influencing our technology and the business direction. He is well known for his leadership in the field of requirements engineering. Al was also active in consulting activities and had developed a number of techniques for helping companies improve their requirements process. These techniques were merged with some of the RELA-derived techniques and became the basis of a professional training offering called Requirements College, the basis for parts of this book.In addition, operating under the insufficiently popular business theory of "you can never have too much professional help," we recruited renowned software author and expert Ed Yourdon to join the board of the company. Ed was also highly influential in guiding the course of the technology and busi-ness direction. Both Ed and Al were earlier contributors to this work, and many of the words that appear in this book are theirs. Indeed, we had intended to release the book jointly a few years ago. But times change, and Ed and Al have graciously donated all of their earlier work to us. However, you will often hear them speaking through these words.Experiences at Rational SoftwareRational Software Corporation purchased Requisite, Inc., in 1997. At Rational, we have gained significant additional experience in requirements management as it applies to developing and releasing a full family of application development tools, as well as continuing to help customers address their requirements problems. Don continues to work with us and help refine the techniques. In addition, at Rational, I have had the pleasure of working with software experts and authors Grady Booch, Ivar Jacobson, James Rumbaugh, Walker Royce, and Philippe Kruchten. Each of them contributed to my view of the requirements management challenge, and Walker and Philippe were early reviewers of this work.We also became exposed to the use case technique for requirements capture. The application of notion of using use cases within the design model pro-vides a common thread to drive architecture, implementation, and testing.I am also a fan of Rational's promulgation of the iterative approach for software development, of which I like to think that we were early practitioners at RELA, as well as the Rational Unified Process, a full life cycle software development process.   Rational helped me complete this work, and for that I am grateful. Also, Rational graciously provided permission to use certain ideas, text, and diagrams.   Finally, we would also like to thank the reviewers and many others who contributed to this work, including Al Davis, Ed Yourdon, Grady Booch, Philippe Kruchten, Leslee Probasco, Ian Spence, Jean Bell, Walker Royce, JoeSummaryIn a sense, few, if any, ideas in this book are original. Instead, it represents harvesting the shared software development experiences of two decades, with a focused, consistent, and measured emphasis on the requirements challenge. In so doing, the work, we hope, assimilates the experiences and opinions of some of the best minds in the industry on this unique and difficult software challenge. We firmly believe that the result--these six requisite team skills for effective requirements management, will help you deliver quality software systems on time and on budget.0201615932P04062001