Week6 - 1 1 CSE 3402 Winter 2012 Fahiem Bacchus& Yves...

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Unformatted text preview: 1 1 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance CSE 3402: Intro to Artificial Intelligence Knowledge Representation & First-Order Logic ● Required Readings: Chapter 8 ● Optional: If you need more background: ■ 7.1-7.3 Motivation for logic, basic introduction to semantics. ■ 7.4-7.5 propositional logic (good background for first- order logic). ■ 7.7 useful insights into applications of propositional logic. 2 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Why Knowledge Representation? ● Consider the task of understanding a simple story. ● How do we test understanding? ● Not easy, but understanding at least entails some ability to answer simple questions about the story. 2 3 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Example. ● Three little pigs 4 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Example. ● Three little pigs 3 5 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Example ● Why couldn ` t the wolf blow down the house made of bricks? ● What background knowledge are we applying to come to that conclusion? ■ Brick structures are stronger than straw and stick structures. ■ Objects, like the wolf, have physical limitations. The wolf can only blow so hard. 6 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Why Knowledge Representation? ● Large amounts of knowledge are used to understand the world around us, and to communicate with others. ● We also have to be able to reason with that knowledge. ■ Our knowledge won ` t be about the blowing ability of wolfs in particular, it is about physical limits of objects in general. ■ We have to employ reasoning to make conclusions about the wolf. ■ More generally, reasoning provides an exponential or more compression in the knowledge we need to store. I.e., without reasoning we would have to store a infeasible amount of information: e.g., Elephants can ` t fit into teacups. 4 7 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Logical Representations ● AI typically employs logical representations of knowledge. ● Logical representations useful for a number of reasons: 8 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Logical Representations ● They are mathematically precise, thus we can analyze their limitations, their properties, the complexity of inference etc. ● They are formal languages, thus computer programs can manipulate sentences in the language. ● They come with both a formal syntax and a formal semantics. ● Typically, have well developed proof theories: formal procedures for reasoning (achieved by manipulating sentences). 5 9 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Set theoretic semantics ● Suppose our knowledge is represented in our program by some collection of data structures. We can think of these as a collection of strings (sentences)....
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This note was uploaded on 02/13/2012 for the course CSE 3402 taught by Professor Yves during the Winter '12 term at York University.

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Week6 - 1 1 CSE 3402 Winter 2012 Fahiem Bacchus& Yves...

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