Case analysis module therac-25, college study notes - Case analysis, Study notes of Software Engineering

Download Case analysis module therac-25, college study notes - Case analysis and more Study notes Software Engineering in PDF only on Docsity! Connexions module: m13765 1 Case Analysis Module: Therac-25 ∗ William Frey This work is produced by The Connexions Project and licensed under the Creative Commons Attribution License † Abstract This module, designed for the EAC Toolkit (NSF SES 0551779) will test the Toolkit and Connexion's ability to network dierent online and oine sources for ethics across the curriculum. It consists of four components designed to provide students with tools for carrying out an in-depth analysis of the cases found at www.computingcases.org; it also makes substantial references to the draft manuscript of a textbook in computer ethics entitled Good Computing: A Virtue Approach to Computer Ethics. (The book will consist of the cases displayed at Computing CasesTherac-25, Hughes Aircraft, and Machado plus seven additional cases all developed through NSF projects DUE-9972280 and DUE 9980768.) The module presents the case abstract and timeline. It then refers students to Computing Cases where they will nd the case narrative, history, and supporting documents that provide background necessary for analysis. The case abstract and timeline introduce students to the basic outlines of the case. The accompanying decision point taken from the case provides students with the necessary focus to carry out an in-depth analysis. Students respond to the decision point by working through four stages: problem specication, solution generation, solution testing, and solution implementation. Computer Ethics Case Module Template By William J. Frey Module Introduction: The Therac-25 case is what Hu and Frey call a thick, historical, evaluative, big news and bad news case. Tackling cases of this complexity requires both careful thought and considerable skill. Especially important is the ability to sift through the case details, documents, and conicting narratives. The purpose of this module is to provide students with a structure to tackle big, long, and complicated cases. Students will receive frameworks to help them structure the case's ethical and social problems. They will also be provided with decision points that will help them to enter into the case and take up the standpoint of a participant. The module presented below can be linked to materials that can be found at www.computingcases.org. Nancy Leveson, in Safeware:System Safety and Computer (515-553), also provides an excellent and comprehensive account. Excellent advice on how to teach the case, updated information, and clear explanations of the programming errors are provided by Chuck Hu and Richard Brown in "Integrating Ethics into a Computing Curriculum: A Case Study of the Therac-25." The materials posted at Computing Cases were all developed through NSF projects DUE-9972280 and DUE 9980768.) The module presents the case abstract and timeline. It then refers students to computingcases.org where they will nd the case narrative, history, and supporting documents that provide background information necessary for analysis. The case abstract and timeline introduce students to the basic outlines of the case. The accompanying decision point taken from the case provides students with the necessary focus to carry out ∗Version 1.8: Oct 10, 2011 7:08 am GMT-5 †http://creativecommons.org/licenses/by/3.0/ http://cnx.org/content/m13765/1.8/ Connexions module: m13765 2 an in-depth analysis. Students respond to the decision-point by working through the four stages: problem specication, solution generation, solution testing, and solution implementation. Module Activities: 1. Instructor introduces the case based on the abstract and timeline found at www.computingcases.org1 2. Students read case abstract, timeline, case decision point, and case analysis exercises. 3. Students do further research into the case by consulting ComputingCases materials which include narratives, histories, supporting documents, and ethical analyses. 4. Students carry out the activities outlined in the accompanying case exercises by (a) specifying the problem raised in the decision point, (b) generating solutions, (c) testing solutions using ethics tests, and (d) developing plans for implementing the solution over situational constraints. 5. Students prepare their case analyses working in small groups. 6. These groups present their completed analysis to the class in a case-debrieng session. 7. The instructor concludes by discussing the problem-solving issues and intermediate moral concepts raised by the case. 1 Therac-25 Abstract Therac-252 was a new generation medical linear accelerator3 for treating cancer. It incorporated the most recent computer control equipment. Therac-25's computerization made the laborious process of machine setup much easier for operators, and thus allowed them to spend minimal time in setting up the equipment. In addition to making setup easier, the computer also monitored the machine for safety. With the advent of computer control, hardware based safety mechanisms were transferred to the software. Hospitals were told that the Therac-25 medical linear accelerator had "so many safety mechanisms" that it was "virtually impossible" to overdose a patient. Normally, when a patient is scheduled to have radiation therapy for cancer, he or she is scheduled for several sessions over a few weeks and told to expect some minor skin discomfort from the treatment. The discomfort is described as being like a mild sunburn over the treated area. But in this case on safety critical software, you will nd that some patients received much more radiation than prescribed Therac - 25 Timeline This time line is largely adopted from the Computing Cases website. The website developer, Charles Hu, has provided this module's author with a more detailed unpublished version (that provides the real names of the patients left out in Computing Cases) that the author has adopted here. Readers should note that this time line also overlaps with that provided by Leveson and Turner. (See below for two references where the Turner and Leveson time line can be found.) 1http://www.computingcases.org/ 2http://www.computingcases.org/case_materials/therac/teaching/therac/supporting_docs/Therac%20Glossary.html#tr25 3http://www.computingcases.org/case_materials/therac/teaching/therac/supporting_docs/Therac%20Glossary.html#tr13 http://cnx.org/content/m13765/1.8/ Connexions module: m13765 5 2c. Use the table to identify and locate value conicts within the STS. Can the problem be specied as a mismatch between a technology and the existing STS, a mismatch within the STS exacerbated by the introduction of the technology, or by overlooked results? STS/Value Safety (free- dom from harm) Justice (Equity & Access) Privacy Property Free Speech Hardware/software Physical Sur- roundings People, Groups, & Roles Procedures Laws Data & Data Structures Table 3 3. Develop a general solution strategy and then brainstorm specic solutions: Problem / So- lution Strategy Disagreement Value Conict Situational Constraints Factual Conceptual Integrate? Tradeo? Resource?Technical?Interest Table 4 3a. Is problem one of integrating values, resolving disagreements, or responding to situational constraints? 3b. If the conict comes from a value mismatch, then can it be solved by modifying one or more of the components of the STS? Which one? 4. Test solutions: Alternative / Test Reversibility Value: Jus- tice Value: Re- sponsibility Value: Re- spect Harm Code A #1 A #2 A #3 Table 5 5. Implement solution over feasibility constraints http://cnx.org/content/m13765/1.8/ Connexions module: m13765 6 Alternative Con- straint Resource Interest Technical Time Cost Individual Organization Legal/ So- cial Available Techno- logy Manufacturability #1 #2 #3 Table 6 2 Appendix Therac Decision Point Presentation [Media Object]4 [Media Object]5 Therac-25 Decision Point [Media Object]6 Therac-25 Case Summary [Media Object]7 Free and Informed Consent, Safety, and Dimensions of Risk [Media Object]8 3 References • Nancy G. Leveson. Safeware: System Safety and Computers. New York: Addison-Wesley Publishing Company, 515-553. • Nancy G. Leveson and Clark S. Turner. An Investigation of the Therac-25 Accidents. Computers, Ethics, and Social Values, Johnson, D.G. and Nissenbaum, H., eds.: 478. • Nancy G. Leveson and Clark S. Turner. An Investigation of the Therac-25 Accidents. IEEE Com- puter. 26(7): 18-41, July 1993. • Computing Cases website. See above link. Materials on case including interviews and supporting documents. • Sara Baase. A Gift of Fire: Social, Legal, and Ethical Issues in Computing. Upper Saddle River, NJ: Prentice-Hall, 125-129. • Chuck Hu. Good Computing: A Virtue Approach to Computer Ethics. Draft for course CS-263. June 2005. • Chuck Hu and Richard Brown. Integrating Ethics into a Computing Curriculum: A Case Study of the Therac-25. Available at Computing Cases website. See above link. 4This media object is a downloadable le. Please view or download it at <http://cnx.org/content/m13765/1.8/Therac-25 Case_V3.pptx> 5This media object is a downloadable le. Please view or download it at <http://cnx.org/content/m13765/1.8/Therac-25 Case_V4.pptx> 6This media object is a downloadable le. Please view or download it at <http://cnx.org/content/m13765/1.8/Therac-25_DP.pptx> 7This media object is a downloadable le. Please view or download it at <http://cnx.org/content/m13765/1.8/Therac-25 Case_V6.pptx> 8This media object is a downloadable le. Please view or download it at <http://cnx.org/content/m13765/1.8/Therac-25 Case_V7.pptx> http://cnx.org/content/m13765/1.8/ Connexions module: m13765 7 • For time line see: http://computingcases.org/case_materials/therac/supporting_docs/therac_resources/Timeline.html • Leveson in Safeware provides an excellence summary of the literature on system safety. For two further excellent resources consult the next two references. • Perrow, C. (1984) Normal Accidents: Living with high-risk technologies. Basic Books, NY,NY. • Reason, J. (1990/1999) Human Error Cambridge University Press: London. http://cnx.org/content/m13765/1.8/