ASSOCIATIVE NETS AND FRAME SYSTEMS Network Representations If L is - - PowerPoint PPT Presentation

Lecture 4 Associative Nets & Frames 1

ASSOCIATIVE NETS AND FRAME SYSTEMS

Network Representations

If L is a set of labeled links and N is a set of nodes, then a network is any subset of N×L×N, where the order of the triples is material.

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Associationist Theories of Meaning

Associationist theories define the meaning of an

• bject in terms of a network of associations

with other objects in a mind or a knowledge base. e.g. through experience we associate the concept

• f snow with other concepts such as cold,

white, snowman, slippery and ice.

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Network Representation of properties

• f snow and ice

ice hard clear

hardness temperature

soft slippery white cold snow snowman

made of texture color temperature color

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Implementing Network Representation in CLIPS

CLIPS> (deftemplate net ;network representation (slot name (type SYMBOL) ) (slot color (type SYMBOL) ) (slot temperature (type SYMBOL) ) (slot texture (type SYMBOL) ) (slot hardness (type SYMBOL) ) ) CLIPS> (deffacts things ;defining two things (net (name snow) (color white) (temperature cold) (texture slippery) (hardness soft)) (net (name ice) (color clear) (texture slippery) (temperature cold) (hardness hard)))

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Implementing Network Representation in CLIPS (contd.)

;Associating snow with something else which is also cold CLIPS> (defrule association (net (name snow) (temperature cold)) (net (name ?Y&~snow) (temperature cold)) => (printout t "snow reminds me of " ?Y crlf))

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Implementing Network Representation in CLIPS (contd.)

CLIPS> (watch facts) CLIPS> (watch rules) CLIPS> (reset) ==> f-0 (initial-fact) ==> f-1 (net (name snow) (color white) (temperature cold) (texture slipper) (hardness soft) ==> f-2 (net (name ice) (color clear) (temperature cold) (texture slippery) (hardness hard) CLIPS> (run) FIRE 1 association: f-1, f-2 snow reminds me of ice

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Semantic Network by Collins & Quillian

can has has is a FISH can is a BIRD ANIMAL Fly Wings Feathers Breathe Skin Sing Yellow CANARY can is Sing Tall OSTRICH cannot is Move has can is a is a

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Human Information Storage and Response Time

1.5 1.4 1.3 1.2 1.1 1.0 0.9 Response Time (sec) A canary is a bird A canary can sing “Complexity” of sentence A canary has skin A canary can fly A canary is a canary A canary is an animal

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Implementing Semantic Nets in CLIPS

CLIPS> (deftemplate species (slot node (type SYMBOL) ) (slot is-a (type SYMBOL) ) (multislot is (type SYMBOL) ) (multislot has (type SYMBOL) ) (multislot can (type SYMBOL) ) (multislot cannot (type SYMBOL) ) ) CLIPS> (deffacts biology (species (node canary) (is-a bird) (is yellow) (can fly) ) (species (node ostrich) (is tall) (cannot fly) (is-a bird) ) (species (node bird) (is-a animal) (can fly) (has wings feather) ) (species (node fish) (is-a animal) ) (species (node animal) (can breathe move) (has bones skin) ) )

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Implementing Semantic Nets in CLIPS (contd.)

CLIPS> (defrule link1 (declare (salience 10)) (species (node ?X)(is-a ?Y&~nil)) => (printout t "A " ?X " is a " ?Y crlf)) CLIPS> (defrule link2 (declare (salience 5)) (species (node ?X) (is-a ?Y)) (species (node ?Y) (is-a ?Z&~nil)) => (printout t "A " ?X " is a " ?Z crlf))

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Implementing Semantic Nets in CLIPS (contd.)

CLIPS> (defrule link3 (species (node ?X) (is-a ?Y)) (species (node ?Y) (is-a ?Z)) (species (node ?Z) (has $?W)) => (printout t "A " ?X " has " (implode$ ?W) crlf))

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Implementing Semantic Nets in CLIPS (contd.)

CLIPS> (reset) CLIPS> (run) A fish is a animal A bird is a animal A ostrich is a bird A canary is a bird A canary is a animal A ostrich is a animal A ostrich has bones skin A canary has bones skin

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Semantic Nets for Natural Language

The word “give” has the following associated roles: a donor, a recipient and an object given.

give person person thing

recipient donor

• bject

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An Instance of a Semantic Net

give-1 john mary book

recipient donor

• bject

Knowledge derived from “John gave Mary a book”.

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Natural Language Grammar Rules

S NP VP

; S=Sentence, NP=Noun Phrase, VP=Verb Phrase

NP Proper_Noun | Article Noun | Noun VP VP PP

; PP=Prepositional Phrase

VP Verb NP PP Prep NP Proper_Noun Sarah Noun chair | glue Article the Prep with

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Natural Language Parsing

S NP VP Proper_Noun Sarah VP PP Verb NP Prep NP Article Noun fixed the chair with glue

Syntactic Analysis:

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Case Frame for English Verbs

Semantic Analysis: Knowledge representation for “Sarah fixed the chair with glue”

fix past chair glue sarah time

• bject

instrument agent

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CLIPS Template for Case Frame

CLIPS> (deftemplate case (slot verb (type SYMBOL) ) (slot agent (type SYMBOL)) (slot object (type SYMBOL) ) (slot time (type SYMBOL) ) (slot instrument (type SYMBOL) ) )

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Structured Representations

• Organizing knowledge into a structure called

frame.

• A frame may be viewed as a data structure

used to represent well-understood stereotyped situations

• Example: birds as prototypical objects with a

general property that most birds can fly though there are exceptions.

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Frame Systems

A frame system attempts to integrate

– Declarative notions about objects and events and their properties, and – Procedural notions about how to retrieve information and achieve goals.

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A Frame

Name: Name-1 Attribute-1: value-1 Attribute-2: procedure-1 . . . . . Attribute-n: value-m Attribute-3: procedure-2 Slots Fillers (procedures are sometimes known as demons)

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Hierarchy of Frames

• Frames are typically arranged in a hierarchy in

which “lower” frames can inherit values from “higher” frames in the hierarchy.

• Properties and procedures for “higher” frames

are more or less fixed whereas “lower” frames may be filled with more contingent information.

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Links in a Frame System

• Instances − Classes
• Classes - Superclasses

Machine Computer SunA SunFire Superclass Class Instances

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Inheritance System of Birds

bird superclass: vertebrate reproduction: lay_eggs covering: feathers can fly: T scavenger superclass: bird diet: (garbage carrion) sparrow superclass: songbird habitat: north america songbird superclass: bird diet: (bugs seeds) canary superclass: songbird habitat: tropical tweety instance of: canary fightless bird superclass: bird can fly: nil penguin superclass: flightless_bird habitat: south pole diet: fish

• pus

instance of: penguin

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Hierarchical Representation for Geometric Figures of Land

Each node in the hierarchy consists of a structure with the following format: NAME: Number of Sides: Length of Sides: Size of Angles: Area: Price of Land:

Polygon Quadrilateral Trapezium Parallelogram Rectangle Square

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Defaults and Demons

Some of the slots in “Polygon” may have the following fillers: Number of Sides: 4 (default) Area: compute_area (IF-NEEDED demon) Price=compute_price(Area) (IF-ADDED demon) Price: receives value from above when Area is added or updated.

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Implementing Frames in CLIPS

CLIPS> (defclass polygon (is-a USER) ) CLIPS> (defclass quadrilateral (is-a polygon) ) CLIPS> (defclass trapezium (is-a quadrilateral) ) CLIPS> (defclass parallelogram (is-a trapezium) ) CLIPS> (defclass rectangle (is-a trapezium) ) CLIPS> (defclass square (is-a rectangle) )

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Abstract and Concrete Classes

CLIPS> (defclass polygon (is-a USER) (role abstract) (slot no_of_sides (default 4) ) ) CLIPS> (defclass quadrilateral (is-a polygon) (role concrete) ) Concrete classes can generate instances while abstract classes will not.

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Defining a demon

CLIPS> (defmessage-handler polygon sides ( ) ?self: no-of-sides) CLIPS> (definstances geometry (square-one of square) ) CLIPS> (send [square-one] sides) 4

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Multiple Inheritance in Heterarchical Representation

Polygon Regular Polygon Triangle Isosceles Triangle Equilateral Triangle Quadrilateral Rectangle Square There is no ambiguity if “Square” inherits different information from “Regular Polygon” and “Rectangle”. The same applies to “Equilateral Triangle”

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Conflicting Defaults among Frames

Person Quaker Republican Republican Quaker

(defclass person (is-a USER) ) (defclass quaker (is-a person) ) (defclass republican (is-a person) ) (defclass republican-quaker (is-a republican quaker) (role concrete) )

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Effect of Class Precedence

CLIPS> (defmessage-handler quaker speak ( ) (printout t crlf “Peace”) ) CLIPS> (defmessage-handle republican speak ( ) (printout t crlf “War”) ) CLIPS> (definstance people (richard of republican-quaker) ) CLIPS> (send [richard] speak) War