1、PART ONE The Product and the Process,Chapter 1 The Product, The Evolving Role of Software,In the early days: User ComputerSoftware = “Place a sequence of instructions together to get the computer to do something useful”.,In late 1950s:Computer became cheaper and more commonHigh level languages were
2、invented,Programmer,In early 1960s:Very few large software projects were done by some experts.,Hacker Cracker,PART ONE The Product,In middle to late 1960s:Truly large software systems were attempted.,Case 1. 美国IBM公司在1963年至1966年开发的IBM360机的操作系统。这一项目花了5000人一年的工作量，最多时有1000人投入开发工作，写出了近100万行源程序。据统计，这个操作系统
3、每次发行的新版本都是从前一版本中找出1000个程序错误而修正的结果。这个项目的负责人F. P. Brooks事后总结了他在组织开发过程中的沉痛教训时说：“正像一只逃亡的野兽落到泥沼中做垂死的挣扎，越是挣扎，陷得越深，最后无法逃脱灭顶的灾难。程序设计工作正像这样一个泥潭，一批批程序员被迫在泥沼中拼命挣扎，谁也没有料到问题竟会陷入这样的困境”。IBM360操作系统的历史教训成为软件开发项目的典型事例为人们所记取。而Brooks博士随后写出了软件工程领域的经典著作人月神话(The Mythical Man-Month)，至今畅销不衰。,Software Crisis ! - NATO Confere
4、nce, Garmisch, Germany, 1968,Or maybe Chronic Affliction is more accurate?,PART ONE The Product,Dramatic improvements in hardware performance Profound changes in computing architectures Vast increases in memory and storage capacity Wide variety of exotic input and output options,Today:,Software =,Pr
5、oduct (information transformer),Vehicle for delivering a product (OS, network, tools), The same questions are still asked today:, Why does it takes so long to get software finished?, Why are development costs so high?, Why cant we find all the errors before we give the software to customers?, Why do
6、 we continue to have difficulty in measuring progress as software is being developed?,PART ONE The Product,PART ONE The Product,A week later the boss called the engineer into his office and asked, “Where are we?”“Everythings going well,” said the youngster, “but Ive run into a few small snags. Ill g
7、et them ironed out and be back on track soon.”“How does the deadline look?” the boss asked.“No problem,” said the engineer. “Im close to 90 percent complete.”If youve been working in the software world for more than a few years, you can finish the story. Itll come as no surprise that the young engin
8、eer stayed 90 percent complete for the entire project duration and only finished (with the help of others) one month late.,Myth: The only deliverable for a successful project is the working program. Reality: A working program is only one part of a software configuration that includes programs, docum
9、ents, and data. Documentation forms the foundation for successful development and, more important, provides guidance for software support.,Managers evaluate, track progress, Programmers communicate to each other Maintainers VITAL!,PART ONE The Product,Case 3. In the early 1980s, the United States In
10、ternal Revenue Service (IRS) hired Sperry Corporation to build an automated federal income tax form processing system. According to the Washington Post, the “system has proved inadequate to the workload, cost nearly twice what was expected and must be replaced soon” (Sawyer 1985). In 1985, an extra
11、$90 million was needed to enhance the original $103 million worth of Sperry equipment. In addition, because the problem prevented the IRS from returning refunds to taxpayers by the deadline, the IRS was forced to pay $40.2 million in interest and $22.3 million in overtime wages for its employees who
12、 were trying to catch up. In 1996, the situation had not improved. The Los Angeles Times reported on March 29 that there was still no master plan for the modernization of IRS computers, only a six-thousand-page technical document. Congressman Jim Lightfoot called the project “a $4-billion fiasco tha
13、t is floundering because of inadequate planning” (Vartabedian 1996).,Myth: Project requirements continually change, but change can be easily accommodated because software is flexible.,PART ONE The Product,Myth: If we get behind schedule, we can add more programmers and catch up. Reality: Software de
14、velopment is not a mechanistic process like manufacturing. In the words of Brooks, “adding people to a late software project makes it later.”,PART ONE The Product,Case 4. 某公园有一游船码头，负责人希望开发一游船管理系统，要求如下：当游客租船时，管理员输入S表示租船周期开始；当游客还船时，管理员输入E表示租船周期结束。一天结束时，要求系统打印出租船次数和平均租船时间。,Algorithm: Number = Total_tim
15、e = 0; Get Message; While ( ! End_of_stream ) if (Code = S) Number +;Total_time = Start_time; else Total_time += End_time;Get Message; Print Number; If (Number) Print Total_time / Number;,新要求：输出一天中的最长租用时间。,新要求：将报告分上午和下午输出。,新要求：当通信线路出问题时，能从计算中删除一切不完整的租船信息。,Myth: Once we write the program and get it t
16、o work, our job is done.Reality: Someone once said that “the sooner you begin writing code, the longer itll take you to get done.” Industry data indicate that between 60 and 80 percent of all effort expended on a program will be expended after it is delivered to the customer for the first time.,PART
17、 ONE The Product, What Is Software ?,Software is a set of items or objects that form a configuration that includes instructions (computer programs) that when executed provide desired function and performance, data structures that enable the programs to adequately manipulate information, and document
18、s that describe the operation and use of the programs.,AND MORE , Software is developed or engineered, it is not manufactured in the classical sense.,High quality is achieved through good design,Depend on people,Require the construction of a “product”,PART ONE The Product, Software doesnt wear out.,
19、But it does deteriorate!,There are no software spare parts , Although the industry is moving toward component-based assembly, most software continues to be custom built.,Myth: Software engineering will make us create voluminous and unnecessary documentation and will invariably slow us down.Reality:
20、Software engineering is not about creating documents. It is about creating quality. Better quality leads to reduced rework. And reduced rework results in faster delivery times.,PART ONE The Product, Software Poses Challenges, How do we ensure the quality of the software that we produce?, How do we meet growing demand and still maintain budget control?, How do we upgrade an aging “software plant?“, How do we successfully institute new software technologies?,
