CS621 : Artificial Intelligence

CS621 : Artificial Intelligence

Pushpak BhattacharyyaCSE Dept., IIT Bombay

Lecture 9

Continuation of Logic and Semantic Web

AI’s view of knowledge

Data

Information

Knowledge

Wisdom

IncreasingComplexity,Sophistication andRefinement.

Every levelContains informationOn HOW the lowerLevel is USED

Fundamental Triple

<Object, Attribute, Value> E.g.,

<Person, Name, ‘Ram’> <City, Population, 500000> <Box, Number, 23>

And so on

Review of Predicate Calculus

Predicate Calculus

Introduction through an example (Zohar Manna, 1974): Problem: A, B and C belong to the Himalayan

club. Every member in the club is either a mountain climber or a skier or both. A likes whatever B dislikes and dislikes whatever B likes. A likes rain and snow. No mountain climber likes rain. Every skier likes snow. Is there a member who is a mountain climber and not a skier?

Given knowledge has: Facts Rules

Predicate Calculus: Example contd. Let mc denote mountain climber and sk denotes skier.

Knowledge representation in the given problem is as follows:

1. member(A)2. member(B)3. member(C)4. ∀x[member(x) → (mc(x) ∨ sk(x))]5. ∀x[mc(x) → ~like(x,rain)]6. ∀x[sk(x) → like(x, snow)]7. ∀x[like(B, x) → ~like(A, x)]8. ∀x[~like(B, x) → like(A, x)]9. like(A, rain)10. like(A, snow)11. Question: ∃x[member(x) ∧ mc(x) ∧ ~sk(x)]

We have to infer the 11th expression from the given 10. Done through Resolution Refutation.

),(~),(~ 44 xBlkxAlike ),( snowAlk

),(~ snowBlk ),()(~ 22 snowxlkxsk

)()()(~ 111 xskxmcxmember )(~ Bsk

)()(~ BmcBmember )(Bmember

)(Bmc)()(~)(~ 666 xskxmcxmember

)()(~ BskBmember )(~ Bsk

)(~ Bmember )(Bmember

710

12 5

13 4

14 2

1115

16 13

17 2

Ontology

Taxonomic organization of knowledge

Simple Inference

Fundamental relationships Hypernymy

Subclass (man mammal Membership (Ram ε man)

Meronymy (part whole) (hand part-of body)

Markup (embeds meta-information) I just got a new dog <sentence>

<person href="http://aaronsw.com/">I</person> just got a new pet <animal>dog</animal>.</sentence>

<sentence><person href="http://aaronsw.com">I</person>

just got a new pet <animal type="dog" href="http://aaronsw.com/myDog">dog</animal>.</sentence>

Namespace Give meaning to a name Specifically, bind a name with an URI

(uniform resource identifier in the web) <aref http://www.cse.iitb.ac.in/~pb>

Pushpak </aref>{person}

<aref http://www.imdb.com/title/tt0251355/> Pushpak </aref>

{movie}

Draw the names from the namespace

<sentence    xmlns="http://example.org/xml/documents/"    xmlns:c="http://animals.example.net/xmlns/"<c:person c:href="http://aaronsw.com/">I</c:person> just got a new pet <c:animal>dog</c:animal>.</sentence>

RDF: Resource Description Format

Each RDF statement has three parts: a subject, a predicate and an object

Makes statements about resources on the web, uniquely identified by URIs

Example (from W3C specification of RDF)

In natural Language http://www.example.org/index.html

has a creator whose value is John Smith http://www.example.org/index.html

has a creation-date whose value is August 16, 1999

http://www.example.org/index.html has a language whose value is English

Subject-Predicate-Object based scheme

the subject is the URL http://www.example.org/index.html

the predicate is the word "creator" the object is the phrase "John

Smith"

More concretely through URIs

a subject http://www.example.org/index.html

a predicate http://purl.org/dc/elements/1.1/creator

and an object http://www.example.org/staffid/85740

In graphical form

With all other information

In triple notation Subject

http://www.example.org/index.html http://purl.org/dc/elements/1.1/creator> http://www.example.org/staffid/85740

Predicate http://www.example.org/index.html <http://www.example.org/terms/creation-date> "August 16, 1999" .

Object http://www.example.org/index.html http://purl.org/dc/elements/1.1/language "en" .