Just Enough Structured Analysis Chapter 1: Introduction “The beginnings and endings of all human undertakings are untidy, the building of a house, the writing of a novel, the demolition of a bridge, and, eminently, the finish of a voyage.” — John Galsworthy Over the River, 1933 www.yourdon.com ©2006 Ed Yourdon - rev. 051406 In this chapter, you will learn: 1. Why systems analysis is interesting; 2. Why systems analysis is more difficult than programming; and 3. Why it is important to be familiar with systems analysis. Chances are that you groaned when you first picked up this book, seeing how heavy and thick it was. The prospect of reading such a long, technical book is enough to make anyone gloomy; fortunately, just as long journeys take place one day at a time, and ultimately one step at a time, so long books get read one chapter at a time, and ultimately one sentence at a time. 1.1 Why is systems analysis interesting? Long books are often dull; fortunately, the subject matter of this book — systems analysis — is interesting. In fact, systems analysis is more interesting than anything I know, with the possible exception of sex and some rare vintages of Australian wine. Without a doubt, it is more interesting than computer programming (not that programming is dull) because it involves studying the interactions of people, and disparate groups of people, and computers and organizations. As Tom DeMarco said in his delightful book, Structured Analysis and Systems Specification (DeMarco, 1978), [systems] analysis is frustrating, full of complex interpersonal relationships, indefinite, and difficult. In a word, it is fascinating. Once you’re hooked, the old easy pleasures of system building are never again enough to satisfy you. This may come as a surprise to you if you have any experience writing computer programs. [1] Programming is enormous fun, and it’s enormously satisfying to see a program execute successfully, especially after spending several hours debugging it. It’s hard to imagine that things could be even more rewarding and exciting when you begin to move away from the computer and the writing of computer programs to study the overall system in which the programs play a part. But by the end of this book, I hope to have convinced you that the real challenge, and the real joy, of working with computer systems is that of carrying out systems analysis. No matter what profession you decide to pursue, it will be important for you to understand what systems analysis is all about. If you work in the computer industry as something other than an electrical engineer or hardware designer, there is a good chance that your career will progress from programmer to systems designer to systems analyst before you finally move on to the ranks of management. [2] www.yourdon.com ©2006 Ed Yourdon - rev. 051406 1.2 Whom this book is intended for This book is intended for two audiences: first, the person who is new to the field of systems analysis, and, second, the experienced systems analyst who needs to acquaint himself with systems modeling tools and techniques that have evolved over the past decade. Many readers will be university computer science students who have completed earlier courses on computer programming; some may be students in a business training program. However, the book should be equally readable by people who have finished their university training and who are now working in industry. Many people in the computer industry spend their first several years working as a computer programmer, and then suddenly find themselves promoted to a position of systems analyst, without ever being told what systems analysis is all about or what a systems analyst does. If you are in such a position, this book is for you. You should also find the book useful if you began working as a systems analyst in the 1970s or 1980s and never had an opportunity to learn about classical analysis methods such as structured analysis, or the newer methods such as object-oriented analysis. More and more often today, people outside the computer profession are finding it necessary to become familiar with the field of systems analysis. If you are a business person or a manager, there is a good chance that you will be involved in a systems analysis activity. You will have systems analysts working for you, spending their time trying to understand what kind of automated system you want them to build. Similarly, if you are an administrator, a clerk, a scientist, a politician, an engineer, or an accountant — or virtually any other professional in today’s society — there is a good chance that you will spend a significant amount of time during your career interacting with systems analysts who will be designing and specifying sophisticated computer systems for you. The more you know about what these people do, and what they expect of you, the better off you will be. Even if you have no expectation of working in a white collar job — that is, even if you expect to be an artist, a writer, a musician, or an athlete — you should know what systems analysis is all about. Citizens in every walk of life are affected by computer systems of all sorts. Even if you never intend to build a computer system or have one built for you, it is inevitable that you will be using computer systems for your banking, for your education, for your interactions with the IRS and Social Security, and for virtually every aspect of your interactions with modern society. As John Gall says in Systemantics (Gall, 1977), No one, these days, can avoid contact with systems. Systems are everywhere: big systems, little systems, systems mechanical and electronic, and those special systems that consist of organized associations of people. In self- defense, we must learn to live with systems, to control them lest they control us. As Humpty Dumpty said to Alice (though in another context): “The question is: which is to be master — that’s all.” To emphasize this point even more, keep in mind that the computer industry represented approximately 8% of the United States GNP in 1985; by 1990, it was expected to represent as much as 15% of the GNP. [3] Almost every product built today by American business has one or more computers embedded within it, and almost every service provided to the marketplace by American business is based on or controlled by a computer system. www.yourdon.com ©2006 Ed Yourdon - rev. 051406 1.3 What this book will do for you A major purpose of this book is to teach you about systems analysis: what it is and how one goes about doing it. But there is more: my real purpose is to excite you, to make you so eager to begin practicing systems analysis that you will want to rush through the last pages of the book and begin working on your first project. Seymour Papert recalls in Mindstorms (Papert, 1980), I found particular pleasure in such systems as the differential gear, which does not follow a simple linear chain of causality since the motion in the transmission shaft can be distributed in many different ways to the two wheels depending on what resistance they encounter. I remember quite vividly my excitement at discovering that a system could be lawful and completely comprehensible without being rigidly deterministic. And as Sir Arthur Stanley Eddington said in Space, Time and Gravitation: An Outline of the General Theory (Eddington, 1987), We have found that where science has progressed the farthest, the mind has but regained from nature that which the mind put into nature. We have found a strange footprint on the shores of the unknown. We have devised profound theories, one after another, to account for its origin. At last we have succeeded in reconstructing the creature that made the footprint. And lo! it is our own. Another purpose of the book is to make you understand and appreciate that we live in a world of systems — and systems within systems, which are part of even larger systems. Thus, everything we do in our personal and professional lives has an impact on the various systems of which we are a part. This “systems thinking” approach is not only vital for professional systems analysts, but for all members of modern society. Alas, this book cannot make you an experienced systems analyst, any more than a book on music theory can make you an experienced pianist. By the end of the book, you will be armed with a tremendous amount of technical information that will help you develop accurate models of complex systems, and you will know the step-by-step techniques for carrying out a systems analysis effort. But you will still need a great deal of real-world work to learn the people skills: how to interview a variety of disparate users to understand the true essence of a system; how to present the results of your systems analysis work so that everyone can see a credible estimate of the costs and benefits of developing a new system; and how to distinguish problems from symptoms. As Barry Boehm pointed out in his classic work, Software Engineering Economics (Boehm, 1981): Each of us as individual software engineers has an opportunity to make a significant positive impact on society, simply by becoming more sensitive to the long-range human relations implications of our work, and by incorporating this sensitivity into our software designs and products. www.yourdon.com ©2006 Ed Yourdon - rev. 051406 It takes some practice to do this well, and to learn how to balance human relations concerns with programming and quantitative economic concerns.