1. Natural Language Understanding
Outline:
Motivation
The SHRINK program
Communicating with language
Syntax
Semantics
Semantic grammars
The STONEWORLD program
CSE (c) S. Tanimoto, Natural Language Understanding

2. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Motivation
Make it easier for people to give commands to computers.
Allow computers to perform language translation.
Allow computers to listen to lectures and read books, in order alleviate the knowledge acquisition bottleneck.
Integrate robots into human society.
CSE (c) S. Tanimoto, Natural Language Understanding

3. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
The SHRINK Program
Holds a conversation with the user.
Illustrates how shallow a program’s knowledge can be and still present an image of understanding.
Demonstrates key ideas from J. Weizenbaum’s ELIZA program, published in 1966.
CSE (c) S. Tanimoto, Natural Language Understanding

4. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Mechanisms in SHRINK
Processing is oriented towards maintaining an illusion of understanding.
Pattern matching used to “parse” user input.
The YOU-ME-MAP function transposes first and second person references.
Keyword-based rules respond to certain topics such as dreams, love, being positive or negative.
Questions to the SHRINK are transformed into questions to the user.
When all other rules fail, PUNT responses are used.
CSE (c) S. Tanimoto, Natural Language Understanding

5. A Sample Dialog with SHRINK
WELCOME TO MY SOFA!
PLEASE ENCLOSE YOUR INPUT IN PARENTHESES.
(hi there)
TELL ME MORE
(i have a little problem)
HOW LONG HAVE YOU HAD A LITTLE PROBLEM?
(ever since i told my girlfriend that i love computers more than her)
ALL IS FAIR IN LOVE AND WAR
(thanks maybe i should have told her that)
BE MORE DECISIVE
(ok)
I SEE
(bye)
GOODBYE
CSE (c) S. Tanimoto, Natural Language Understanding

6. Communicating with Language
Language is for communication.
Communication usually means sending and receiving information.
Sentences describe events, states of the world, objects and ideas, feelings and attitudes, and hypothetical situtations.
Phrase-structure grammars provide a method of structuring messages, allowing for a great variety of possible meanings.
CSE (c) S. Tanimoto, Natural Language Understanding

7. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Syntax
Describes the form, not meaning, of sentences in a language.
Syntax is traditionally described with formal systems called grammars.
A context free grammar can be specified with 4 components:
G = (Σ, V, S, P), where
Σ is a finite set of terminal symbols called the alphabet.
V is a finite set of nonterminal symbols.
S is a distinguished member of V called the start symbol.
P is a finite set of productions.
CSE (c) S. Tanimoto, Natural Language Understanding

8. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Example Grammar
G = ({0, 1}, {S, A, B}, S, P), where
P = {
S -> 01S
S -> 10S
S -> 0S1
S -> 1S0
S -> 01
S -> 10 }
CSE (c) S. Tanimoto, Natural Language Understanding

9. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Example Grammar 2
G = ({symbols, are, tools}, {S, N, V}, S, P), where
P = {
S -> NVN
N -> symbols
N -> tools
V -> are }
A derivation of a sentence from S:
S -> NVN -> tools VN -> tools are N -> tools are symbols
Each item in the sequence is a sentential form.
CSE (c) S. Tanimoto, Natural Language Understanding

10. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Exercise
For each of the strings below, determine whether or not it is in L(G), the language generated by G.
If it’s in the language, give a derivation. 01 λ
011001
01S10
101S101
G = ({0, 1}, {S, A, B}, S, P), where
P = {S -> 01S, S -> 10S, S -> 0S1, S -> 1S0, S -> 01, S -> 10}
CSE (c) S. Tanimoto, Natural Language Understanding

11. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Semantics
Representation of meaning using case frames.
The verb structures the frame:
“Alexander took an exam.”
Agent: Alexander
Action: take (write, submit to)
Object: exam
Time: past
CSE (c) S. Tanimoto, Natural Language Understanding

12. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Semantic Grammar
A semantic grammar is a grammar whose syntactic categories correspond directly to groups of words whose meanings can be largely inferred from the parse.
<command> -> <do-word> the <job-word>
<do-word> -> do | perform | start | finish
<job-word> -> job | task | command | activity | operation
“start the activity”
“do the operation”
“finish the job”
CSE (c) S. Tanimoto, Natural Language Understanding

13. Augmented Transition Nets
An ATN is a language processor that combines parsing and translation. It is based on a collection of transition diagrams.
<command>
the
<do-word>
<job-word>
<do-word>
do, etc.
<job-word>
job, etc
CSE (c) S. Tanimoto, Natural Language Understanding

14. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Stone World
A microworld:
2-D cellular space in which various objects can be placed.
An agent “Mace” that takes commands from the user, and which inhabits the microworld.
Stationary objects: pillars, wells, quarries.
Portable objects: stones, gems.
Actions: Mace can move and can carry objects.
A natural-language interface:
Augmented transition network based on a semantic grammar.
CSE (c) S. Tanimoto, Natural Language Understanding

15. Stone World Motivation
Demonstrates a full combination of syntax, semantics, actions, and responses.
An artificial, closed world permits unambiguous interpretation.
Stone World offers a substrate upon which experiments can games can be constructed.
Stone World, while simple by comparison, shares these features with the well-known research system SHRDLU, developed by Terry Winograd at MIT.
CSE (c) S. Tanimoto, Natural Language Understanding

16. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Stone World’s ATN *
TO (DNP1)
TOWARD (DNP1) G2 G3 *
SHOW *
(GO-VERB) G1 T2 T3 T4
LAST
(TAKE-VERB)
UP,
(NP1) * G1
DOWN, 
DOWN, 
(PUT-VERB) P2 P3 IT
CSE (c) S. Tanimoto, Natural Language Understanding

17. Stone World’s ATN (Cont)
NP1
NP2
(ARTICLE)
(OBJ-NOUN)
(OBJ-NOUN)
DNP1
DNP2
(ARTICLE)
(DIRECTION-NOUN)
CSE (c) S. Tanimoto, Natural Language Understanding

18. CSE 415 -- (c) S. Tanimoto, 2001 Natural Language Understanding
Sample Conversation
WALK NORTH *
I UNDERSTAND YOU. OK
GO TO THE WEST *
GO WEST *
TAKE A STONE FROM THE QUARRY *
DROP THE STONE TOWARD THE EAST *
TAKE A STONE *
DROP IT TO THE NORTH *
GO SOUTH *
CSE (c) S. Tanimoto, Natural Language Understanding