Created by, Tom Rebold, MPC FLUENCY WITH INFORMATION TECNOLOGY Skills, Concepts, and Capabilities

Created by, Tom Rebold, MPC

FLUENCY WITH INFORMATION TECNOLOGY

Skills, Concepts, and Capabilities


Algorithms and Digitizing Information

PART 2


TO ERR IS HUMAN

An Introduction to Debugging

chapter7

Precision and AmbiguityDebugging: Isolating the ProblemHTML DebuggingNo Printer Output: A Classic Scenario

To err is human, to really foul things up takes a computer

Copyright © 2003 Pearson Education, Inc. Slide 1-4

Figure 7.1. The Harvard Mark II logbook noting “First actual case of bug being found,” from the Smithsonian Institution.

5

Precision Problems

• How do you say 555-7601 ?

• Need to use “zero” instead of “oh”– Some computers can catch these errors

• [email protected] or [email protected] ?

Fonts matter:• [email protected] or [email protected] ?

• Why can’t computers flag these errors?

mailto:[email protected]




6

Lexical Structures

• When entering boxes on forms (field inputs), each field has rules about what is legal or not (lexical structure)

• What are some rules for – Entering grades?– Phone numbers? – E-mail addresses?

• Since case sometimes matters, when in doubt, be as exact as you possibly can

7

Debugging

• People troubleshoot all the time– Car doesn’t start– VCR doesn’t work – Find and repair a faulty part

• Sometimes there is a logical design error– System was designed incorrectly – You can’t always rely on a computer system

• Sometimes you settle for a work around

8

Debugging Principles

• Make sure you can reproduce the error • Determine exactly what the problem is • Eliminate the obvious causes • Divide the process, separate parts that

work from parts that don’t • When stuck, ask where you may be

making wrong assumptions • Make predictions about what should

happen if you try something

9

HTML Debugging

http://terra.mpc.cc.ca.us/~mpc01a30/temples.htmlhttp://terra.mpc.edu/~mpc01a30/temples.html

http://terra.mpc.cc.ca.us/~mpc01a30/temples.html

http://terra.mpc.edu/~mpc01a30/temples.html

10

HTML Source Code (w/bugs)<html><head><title>Japan Page</title></head> <body bgcolor="black"><font color="white"> <table>

<tr> <td> <a href="tokyo.html"> Tokyo</a></td> <td> <a href="kyoto.html"> Kyoto</a></td> <ta> <a href="osaka.html"> Osaka</a></td> <td> <a href="hiro.html"> Hiroshima</a></td> <td> <a href="yoko.html"> Yokohama</a></td> <td> <a href="fukuoka.html">Fukuoka</a></td> <td> <a href="sapp.html"> Sapporo</a></td> <td> <a href="oki.html"> Okinawa</a></td> <td> <a href="oni.html"> Onimichi</a></td> </tr> </ table> <hl>Japan! </hl> <h2><font face="Helvetica"><At Heian Shrine</font></h2> <img align="left" src="tang.jpeg" width="234" height="296"> <p> <b>In Japan people visit the temples and shrines

for the perspective they give. </b></p> </body></html>

11

Debug Post-mortem

• Summarize changes made

• Summarized unnecessary changes

• Number of errors found—sometimes more than originally observed (hidden errors)

• Most errors are tiny (1 letter)– With huge effects

12

No Printer Output

• We can debug systems we don’t understand

• Reproduced error, understand problem, check obvious

• How to isolate the problem

• Finding the print queue

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Created by, Tom Rebold, MPC FLUENCY WITH INFORMATION TECNOLOGY Skills, Concepts, and Capabilities