Evolutionary Model Prototyping- \Do it twice to assess feasibility to verify requirements May only be a front end or executable specification Or develop system with less functionality or quality attributes °3 approaches:

Abstract Model Specifications Build an abstract model of required software behavior using mathematically defined(perhaps using axioms )types(e. g sets, relations) Define operations by showing effects of that operation on the model Specification includes Model

Outline: Software Design Goals History of software design ideas Design principles Design methods Life belt or leg iron?(Budgen)

Formal design Reviews Associated with each of documentation phases Evaluate with respect to Customer requirements Prescribed standards and practices Contractual requirements

Reuse (Assume have source code, not a commercial product) Ariane 5. Therac-25. British AtC Expectation Significantly lower development costs and time. Amortize costs among all users or uses Assumptions

1. When you can measure what you are speaking about, and can express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowleage is of a meagre and unsatisfactory kind: It may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science. Lord Kelvin, a physicist

opyright Nancy Leveson, Sept. 1999 Stage 1: Forming Team members begin to discover what behaviors are acceptable Usually highly unstructured environment Attempt to identify tasks, how to accomplish them Decisions on what information is needed Hesitant participation

Programming Languages As difficult to discuss rationally as religion or politics. Prone to extreme statements devoid of data. Examples: \It is practically impossible to teach good programming to students that have had a prior exposure to BASIC; as potential programmers they are mentally mutilated beyond hope of regeneration.\(Dijkstra)

第一章软件工程 第二章数据结构 第三章操作系统 第四章数据库技术 第五章面向对象程序设评 第六章计算机网络 第七章网页设计

据统计表明,软件测试工作量 工往往占软件开发总工作量的40% 以上。对于一些涉及到人身安全 的特殊软件,其软件的测试费用 程原理 甚至高于该软件其他费用总和的 3到5倍