Subtle intermittent bug hard to detect other bugs

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Unformatted text preview: t setup positions came up “1” if incorrect, otherwise zero. However, it was stored in ONE BYTE. Every 256th time the routine was called, the flag overflowed and showed a value of zero anyhow. (Subtle, intermittent bug; hard to detect.) ❚ Other bugs sometimes allowed the machine to ignore changes or corrections made by the operator (edits not passed in real time). CIS 350 Lecture 7 © Roxanne Hiltz and Eli Rohn 20 10 Spring 2000 - Lecture 7 Therac 25: What went wrong? ❚ Manufacturer was informed of the incidents (several times) but responded that the machine could not possibly be responsible for the massive overdoses. ❚ Later, some machines removed from service and modified by manufacturer; but did not catch ALL the bugs before returned to service. CIS 350 Lecture 7 21 Therac 25: What went wrong? ❚ This case illustrates many of the things that a responsible, ethical company would not do. CIS 350 Lecture 7 © Roxanne Hiltz and Eli Rohn 22 11 Spring 2000 - Lecture 7 Expert Systems In Medicine ❚ Expert systems are an applied type of Artificial Intelligence ❚ To develop an expert system, AI researchers spend years picking the brains of human experts, extracting their knowledge and trying to understand the way it is organized CIS 350 Lecture 7 23 An Expert System Includes 1. A problem statement with a goal: limited domain-2. A knowledge base 3. A problem solving strategy that determines which knowledge to apply and constructs the lines of reasoning. ("heuristics on next slide) CIS 350 Lecture 7 © Roxanne Hiltz and Eli Rohn 24 12 Spring 2000 - Lecture 7 An Expert System Includes Heuristics are intellectual rules of thumb, or the method by which human experts make "good guesses." 4. A friendly interface that is "natural" to the user CIS 350 Lecture 7 25 Examples Of Expert Systems: ❚ MYCIN is the classic example of an expert system. ❙ It was created around 1972 to diagnose and propose treatments for bacterial infections. infections. ❙ It uses a probabilistic form of backward rule chaining, where assertions are tagged with certainty factors of –1 (false), through 0 (balanced) to 1 (true) ❚ PUFF helps diagnose lung pr...
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This document was uploaded on 03/31/2014 for the course CS 350 at NJIT.

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