ENGS Lecture 5 ENGS 4 - Lecture 5 Technology of Cyberspace Winter 2004 Thayer School of Engineering Dartmouth College Instructor: George Cybenko, x Assistant: Sharon Cooper (“Shay”), x Course webpage:

ENGS Lecture 5 Today’s Class Chad’s presentation Discuss Assignment (due today) Images in web pages and links Break Mini-lecture “Predicting the Future” theme Logical reasoning in expert systems –decision trees, forward and backward chaining Applications of rule-based systems

ENGS Lecture 5 Chad Part II

ENGS Lecture 5 HW Questions?

ENGS Lecture 5 Images in web pages Absolute vs relative addresses Copyright issues Background – images/patterns and colors

ENGS Lecture 5 Break

ENGS Lecture 5 Mini-lecture or open mic

ENGS Lecture 5 “Predicting the Future” Technologies for predicting the future Start with methods based on Aristotelian logic Rule-based, expert systems, etc.

ENGS Lecture 5 Reasoning in rule-based systems Decision trees –diagnosis, troubleshooting, etc –answer to a question leads to another question –displayed graphically, resembles a tree fever? rash?vomiting? yes noyes no

ENGS Lecture 5 Reasoning in rule-based systems Theorem proving (forward chaining) –start with true predicates and rules and conclusion you want to “prove”, say Z –repeatedly apply deduction, syllogism –example: A, B, C, D, E true “rules” –If (A and B) then H –If (D or H) then J –If (J and C) then V –If ( ) then Z –stop when conclusion is found to be true

ENGS Lecture 5 Reasoning in rule-based systems Theorem proving (backward chaining) –start with true predicates and rules and conclusion you want to “prove”, say Z –working backwards from Z, keep track of what predicates have to be true for Z to be true –when all such predicates are known to be true, stop –Example: Z is “Smith murdered Jones” –if ((x has a motive) and (x had the means) and (x can be placed at the scene)) then (x murdered Jones)

ENGS Lecture 5

Aristotelian Science “Women have fewer teeth than men” Law: civil and religious Physics Crisis: Rules cannot explain the physical world. Why do all objects irrespective of mass fall at the same rate? Galileo. Why do things fall? Newton. Hilbert’s program (1900), Gödel’s incompleteness results (1931)

ENGS Lecture 5 Applications Accounting Financial Advising Medical Diagnosis Ancient Astronomy Maintenance (troubleshooting) Others….