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

State Machine specifications Define behavior using states and transitions between states

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

design: added inheritance, multiple inheritance, and polymorphism to ADT In process added complexity and increased some types of connectivity Lots of claimed advantages -- so far empirical evaluation is not supporting them well

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

Requirements specification: A structured document that sets out the services the system is expected to provide Should be precise so that it can act as a contract between the system procurer and software developer and thus needs to be understandable by procurers and developers

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:

Too complex for complete analysis Separation into non-interacting subsystems distorts the results The most important properties are emergent Too organized for statistics Too much underlying structure that distorts the statistics Organized Complexity\(Weinberg) Copyright Nancy Leveson, Sept 1999

Is there a problem? Why Hard? Syllabus EXamples AAS(FAA Advanced Automation System) FBI CIC IRS Modernization Program

以往视觉方法特点: 作为主体的视觉系统被动地接收外界的信息 处理过程复杂、难以实现而且没有充分考虑生物视觉的特点 以往视觉方法忽略的问题: 中央凹(Fovea)的高分辨能力和视网膜上其它部分(不妨称之为外围视觉)的相对较低的分辨能力之间的差异