chapter 7: computer reliability
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Ethics for the Information Age Forth Edition by Michael J. Quinn. Chapter 7: Computer Reliability. Chapter Overview. Introduction Data-entry or data-retrieval errors Software and billing errors Notable software system failures Therac-25 Computer simulations Software engineering - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 7: Computer Reliability
Ethics for the Information AgeForth Edition
by Michael J. Quinn
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Chapter Overview
• Introduction• Data-entry or data-retrieval errors• Software and billing errors• Notable software system failures• Therac-25• Computer simulations• Software engineering• Software warranties
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Introduction
• Computer systems are sometimes unreliable– Erroneous information in databases– Misinterpretation of database information (similar
names)– Malfunction of embedded systems (fatal errors)
• Effects of computer errors– Inconvenience– Bad business decisions– Fatalities
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Data-Entry or Data-Retrieval Errors
• A computerized system may fail because wrong data entered into it
• A computerized system may fail because people incorrectly interpret data they retrieve
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Disfranchised Voters
• November 2000 general election• Florida disqualified thousands of voters• Reason: People identified as felons• Cause: Incorrect records in voter database• Consequence: May have affected
election’s outcome
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False Arrests
• Sheila Jackson Stossier mistaken for Shirley Jackson– Arrested and spent five days in detention
• Roberto Hernandez mistaken for another Roberto Hernandez– Arrested twice and spent 12 days in jail
• Terry Dean Rogan arrested after someone stole his identity– Arrested five times, three times at gun point
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Position of Privacy Advocates
• Number of records is increasing• More erroneous records more false
arrests• Accuracy of crime records more important
than ever
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Software and Billing Errors
• Assume data correctly fed into computerized system
• System may still fail if there is an error in its programming
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Errors Leading to System Malfunctions
• Qwest sends incorrect bills to cell phone customers ($600/minute)– A bill of more than $57,000 for a customer
• Spelling and grammar error checkers increased errors (University documents)
• BMW on-board computer failure (Thailand finance minister was trapped in his BMW)
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Errors Leading to System Failures
• Temporarily out-of-control Boeing 777 (Malaysian plane over the Indian ocean-autopilot error)
• Japan’s air traffic control system• London International Financial Futures and
Options Exchange
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Analysis: E-Retailer Posts Wrong Price, Refuses to Deliver
• Amazon.com in Britain offered iPaq (handheld computers) for £7 instead of £275
• Orders flooded in• Amazon.com shut down site, refused to
deliver unless customers paid true price• Was Amazon.com wrong to refuse to fill
the orders?
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Notable Software System Failures• Patriot Missile (28 soldiers killed) –
insufficient precision in an floating-point variable (system clock)
• Ariane 5 ($500 million not insured) – Integer overflow error
• AT&T long-distance network (70 million calls couldn’t be made and 60,000 people lost service)
• Direct recording electronic voting machines• Therac-25 (3 patients killed out of 6
patients) SW error resulted in overdoses.
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Direct Recording Electronic Voting Machines
• After problems with 2000 election, Congress passed Help America Vote Act of 2002
• Provided money to states to replace punch card voting systems
• Many states used funds to purchase direct recording electronic (DRE) voting machines
• Brazil and India have run national elections using DRE voting machines exclusively
• In November 2006 1/3 of U.S. voters used DRE voting machines
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Issues with DRE Voting Machines
• Voting irregularities– Failure to record votes– Overcounting votes– Misrecording votes
• Lack of a paper audit trail• Vulnerability to tampering• Source code a trade secret, can’t be examined• Possibility of widespread fraud through malicious
programming
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Moral Responsibility of theTherac-25 Team
• Conditions for moral responsibility– Causal condition: actions (or inactions) caused the
harm– Mental condition
• Actions (or inactions) intended or willed -OR-• Moral agent is careless, reckless, or negligent
• Therac-25 team morally responsible– They constructed the device that caused the harm– They were negligent
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Uses of Computer Simulations
• Simulations replace physical experiments. Why?– Experiment too expensive or time-consuming– Experiment unethical– Experiment impossible (evolution of the universe)
• Examples of uses of simulations:– Model past events (Evolution of the universe)– Understand world around us (Search for Oil)– Predict the future (weather predictions)
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Validating Simulations
• Erroneous Simulation because of :– Bugs in SW– Model uses SW is flawed
• Solutions:– Verification: Does program correctly implement model?– Validation: Does the model accurately represent the real
system?
• Validation methods– Make prediction, wait to see if it comes true (Car crash)– Predict the present from old data (Weather forecast)– Test credibility with experts and decision makers
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Software Engineering
• SE is a four steps process:– Specs: determine the functions to be
performed
– Development: produce SW that meet specs.
– Validation: testing the SW
– Evolution: Modify SW to meet change requirements
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Software Engineering: Specification
• Followed SW Crises in 1960s• Specifications of SE:
– Determine system requirements– Understand constraints– Determine feasibility (Budget and schedule)
• End products– High-level statement of requirements (Summary)– Mock-up of user interface– Low-level requirements statement (Detailed)
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Software Engineering: Development
• Create high-level design• Discover and resolve mistakes, omissions
in specification• CASE tools to support design process• Object-oriented systems have advantages• After detailed design, actual programs
written• Result: working software system
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Software Engineering: Validation (Testing)
• Ensure software satisfies specification• Ensure software meets user’s needs• Challenges to testing software
– Noncontinuous responses to changes in input. No identical data set of inputs
– Exhaustive testing impossible. Infinite number of different inputs
– Testing reveals bugs, but cannot prove none exist
• Test modules, then subsystems, then system
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Software Quality Is Improving
• Standish Group tracks IT projects• Situation in 1994
– 1/3 projects cancelled before completion– 1/2 projects had time and/or cost overruns– 1/6 projects completed on time / on budget
• Situation in 2006– 1/6 projects cancelled– 1/2 projects had time and/or cost overruns– 1/3 projects completed on time / on budget
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Shrinkwrap Warranties
• Some say you accept software “as is”• Some offer 90-day replacement or money-
back guarantee• None accept liability for harm caused by
use of software
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Moral Responsibility of Software Manufacturers
• If vendors were responsible for harmful consequences of defects– Companies would test software more– They would purchase liability insurance– Software would cost more– Start-ups would be affected more than big companies and thus– Less innovation in software industry– Software would be more reliable
• Making vendors responsible for harmful consequences of defects may be wrong
• Consumers should not have to pay for bug fixes