ASSOCIATIVE NETS AND FRAME SYSTEMS

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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. Lecture 4 Associative Nets & Frames 1

2 Associationist Theories of Meaning Associationist theories define the meaning of an object 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 of snow with other concepts such as cold, white, snowman, slippery and ice. Lecture 4 Associative Nets & Frames 2

3 Network Representation of properties of snow and ice snowman made of snow hardness soft clear texture slippery ice color temperature cold temperature hard color white Lecture 4 Associative Nets & Frames 3

4 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))) Lecture 4 Associative Nets & Frames 4

5 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)) Lecture 4 Associative Nets & Frames 5

6 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 Lecture 4 Associative Nets & Frames 6

7 Semantic Network by Collins & Quillian Wings Feathers Fly has has can is a BIRD can ANIMAL has can is a FISH Breathe Skin Move is a is a can CANARY is cannot OSTRICH is Sing Yellow Sing Tall Lecture 4 Associative Nets & Frames 7

8 Human Information Storage and Response Time Response Time (sec) A canary can sing A canary has skin A canary can fly A canary is an animal A canary is a bird A canary is a canary Complexity of sentence Lecture 4 Associative Nets & Frames 8

9 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) ) ) Lecture 4 Associative Nets & Frames 9

10 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)) Lecture 4 Associative Nets & Frames 10

11 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)) Lecture 4 Associative Nets & Frames 11

12 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 Lecture 4 Associative Nets & Frames 12

13 Semantic Nets for Natural Language The word give has the following associated roles: a donor, a recipient and an object given. person recipient give donor person object thing Lecture 4 Associative Nets & Frames 13

14 An Instance of a Semantic Net Knowledge derived from John gave Mary a book. mary recipient give-1 donor john object book Lecture 4 Associative Nets & Frames 14

15 Natural Language Grammar Rules S NP VP NP Proper_Noun Article Noun Noun VP VP PP VP Verb NP PP Prep NP Proper_Noun Sarah Noun chair glue Article the Prep with ; S=Sentence, NP=Noun Phrase, VP=Verb Phrase ; PP=Prepositional Phrase Lecture 4 Associative Nets & Frames 15

16 Natural Language Parsing Syntactic Analysis: S NP VP Proper_Noun VP PP Verb NP Prep NP Article Noun Sarah fixed the chair with glue Lecture 4 Associative Nets & Frames 16

17 Case Frame for English Verbs Semantic Analysis: Knowledge representation for Sarah fixed the chair with glue time past sarah agent fix object chair instrument glue Lecture 4 Associative Nets & Frames 17

18 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) ) ) Lecture 4 Associative Nets & Frames 18

19 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. Lecture 4 Associative Nets & Frames 19

20 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. Lecture 4 Associative Nets & Frames 20

21 A Frame Slots Name: Name-1 Attribute-1: value-1 Attribute-2: procedure-1 Attribute-3: procedure Attribute-n: value-m Fillers (procedures are sometimes known as demons) Lecture 4 Associative Nets & Frames 21

22 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. Lecture 4 Associative Nets & Frames 22

23 Links in a Frame System Instances Classes Classes - Superclasses Machine Superclass Computer Class SunA SunFire Instances Lecture 4 Associative Nets & Frames 23

24 Inheritance System of Birds bird superclass: vertebrate reproduction: lay_eggs covering: feathers can fly: T fightless bird superclass: bird can fly: nil songbird superclass: bird diet: (bugs seeds) scavenger superclass: bird diet: (garbage carrion) penguin superclass: flightless_bird habitat: south pole diet: fish canary superclass: songbird habitat: tropical sparrow superclass: songbird habitat: north america opus instance of: penguin tweety instance of: canary Lecture 4 Associative Nets & Frames 24

25 Hierarchical Representation for Geometric Figures of Land Polygon Quadrilateral Trapezium Parallelogram Rectangle 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: Square Lecture 4 Associative Nets & Frames 25

26 Defaults and Demons Some of the slots in Polygon may have the following fillers: Number of Sides: 4 Area: compute_area (default) (IF-NEEDED demon) Price=compute_price(Area) (IF-ADDED demon) Price: receives value from above when Area is added or updated. Lecture 4 Associative Nets & Frames 26

27 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) ) Lecture 4 Associative Nets & Frames 27

28 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. Lecture 4 Associative Nets & Frames 28

29 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 Lecture 4 Associative Nets & Frames 29

30 Multiple Inheritance in Heterarchical Representation Polygon Triangle Quadrilateral Isosceles Triangle Regular Polygon Rectangle Equilateral Triangle Square There is no ambiguity if Square inherits different information from Regular Polygon and Rectangle. The same applies to Equilateral Triangle Lecture 4 Associative Nets & Frames 30

31 Conflicting Defaults among Frames Quaker Person Republican Quaker Republican (defclass person (is-a USER) ) (defclass quaker (is-a person) ) (defclass republican (is-a person) ) (defclass republican-quaker (is-a republican quaker) (role concrete) ) Lecture 4 Associative Nets & Frames 31

32 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 Lecture 4 Associative Nets & Frames 32

Object-based representation. Objects

Object-based representation. Objects Object-based representation Luger, Part III, 6.0, 6.1, 6.2.2-6.2.4, 6.4 (skim) Objects Two basic forms of Structured Objects Semantic Nets Frames Semantic Nets (Associative Nets) Components Nodes - represent