Problem Trends Why Hard? Slyllabus What about software? 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 c Nancy Leveson, Sept. 1999 a0 a1 a1 a3 a3 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 Problem Trends Why Hard? Slyllabus a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 Other Factors a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a5 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 a6 Large discrete state spaces Continuous vs. discrete math Lacks repetitive structure found in computer circuitry Cannot test exhaustively Intangibility a2 a2 Invisible interfaces Hard to experiment with and manage Transient hardware faults vs. software errors a4 a4 Hard to diagnose problems Copyright c Nancy Leveson, Sept. 1999 a7 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 a8 Problem Trends Why Hard? Slyllabus And One More a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 a9 No historical usage information to allow measurement, evaluation, and improvement of standard designs over time. Always specially constructed. Usually doing new things. c Copyright Nancy Leveson, Sept. 1999 a10 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 a11 Problem Trends Why Hard? Slyllabus a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 Class Objectives a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 a12 1. Students will be able to evaluate software engineering techniques and approaches. "It is important that students bring a certain ragamuffin barefoot irreverance to their studies. They are here not to worship what is known, but to question it." Jacob Bronowski, The Ascent of Man "The developed theories ...have rarely been subjected to empirical testing, and so their value remains unknown. They provide zealots with opportunities to market a rash of seminars and courses and to flood the literature with papers advocating the new technologies. When the theories are subjected to testing, what little evidence has been obtained sometimes suggests that the claimed benefits, in fact, may not exist. Vessey and Weber c Copyright Nancy Leveson, Sept. 1999 a13 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 a14 Problem Trends Why Hard? Syllabus Class Objectives a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 a15 2. Students will be able to exercise professional judgment in selecting an approach for a particular project based on an understanding of: How the present state of software practice came about What was tried in the past What worked and what did not work Why c Copyright Nancy Leveson, Sept. 1999 a16 a17 a19 a17 a18 a19 a20 Problem Trends Why Hard? Syllabus Required Background Assignments No programming Reading summaries: Main ideas or themes Critical evaluation Any additional thoughts Some additional short assignments c Copyright Nancy Leveson, Sept. 1999 a21 Problem Trends Why Hard? Syllabus Reading: Both classic papers and new ones I would like to see computer science teaching set deliberately in a historical framework.... The absence of this element in their training causes people to approach every problem from first principles. They are apt to propose solutions that have been found wanting in the past. Instead of standing on the shoulders of their precursors, they try to go it alone. Maurice Wilkes c Copyright Nancy Leveson, Sept. 1999 a22