Inheritance and Default Inheritance in Cognitive Science. Characteristics of computer terminals or MS-DOS OS:

Transcription

1 Inheritance and Default Inheritance in Cognitive Science I Inheritance Characteristics of computer terminals or MS-DOS OS: dimensions (length, width) cursor position colour border A Window is a kind of Screen all of the properties of a Screen sizing (made larger or smaller) positioning multiple instances on a single screen specialised border called a shadow scroll bars title. 1

2 Menus are specialised kinds of Windows. most of the properties of Windows but not scroll bars prompts messages pulldowns Summary a Window isa (kind of) Screen a Menu isa (kind of) Window II Default Inheritance The Menu class inherits all of the characteristics of both the Screen and the Window class, but it will have its own distinctive properties, and in the case of scroll-bars, the property of having a scroll-bar will be overridden, as menus don t have scroll bars. 2

3 III Inheritance & Default Inheritance Are Massively Present Inheritance: sparrows inherit (1). (1) Birds fly. (2) Sparrows are birds. (3) : Sparrows fly. Default inheritance: ostriches don t inherit (1). (4) Ostriches are birds. (5) Ostriches can t fly. (6) : *Ostriches fly. (1) is only inherited by default, and can be overridden by a more specific bit of contradictory information. Default inheritance allows generalizations with exceptions. This allows concepts to have untypical members as well as typical ones. Grammatical categories are prototypes categories defined in terms of their typical members. 3

4 Simple examples of default inheritance in grammar parent-demand A word has (i.e. must have) a parent (default) A finite verb isa word A finite verb may (i.e. doesn t have to) have a parent (override) : *A finite verb has a parent i. The world is round. ( is has no parent) ii. They say that the world is round. ( that is the parent of is ) dependence-demand A preposition has a complement. (default) INSIDE isa preposition. INSIDE may have a complement. (overide) : *INSIDE has a complement i. I left it inside (the house). 4

5 strong verb morphology The shape of the past tense of a verb = its root + {ed}. (default) SEE isa verb. The shape of the past tense of SEE = {saw}. (override) : *The shape of the past tense of SEE = {{see} {ed}}. (I.e. the shape {saw} overrides the shape {{see} {ed}}). 5

6 IV Multiple Inheritance Massively Present Despite Potential Problems Inheritance Conflicts: The Nixon diamond Nixon is a Republican Nixon is a Quaker a Republican is a warmonger a Quaker is a pacifist Crash!!! (a person cannot be both pro- and anti-war) Resolution: Nixon may have opted for Quaker values as he led the U.S. out of the war with Vietnam A dog is a pet and A dog is an animal DOG is an N(oun) and DOG is an s(ubject) 6

7 V Hierarchical nature of information storage In research done in the late 1960s, subjects were asked questions about different properties of birds: Is a canary a bird? Can a canary sing? Can a canary fly? Reaction times differed. E.g. it took longer to answer Can a canary fly? than Can a canary sing? Why? Answer: information stored at most abstract level. Instead of storing separately the facts that canaries fly sparrows fly robins fly we store fact that birds fly and deduce fact that canaries fly by first deducing that canaries are birds. More general properties such as having skin, breathing, etc. stored at an animal level. 7

8 This means that knowledge is stored hierarchically, we predict the fastest reaction times for traits that are specific for canaries such as singing or being yellow and the longest times for traits that are the most general, such as having skin. Hierarchical knowledge of this type is represented in an isa network. We use a triangle with its base along the more general and its apex pointing to the more specific to represent this relation. VI The nature of linguistic knowledge Word type hierarchy shows inheritance and default inheritance In morphology a word s form is inherited from its lexeme and its inflection 8