Interpretation as Abduction Maurizio Atzori
atzori@di.unipi.itInterpretation as Abduction (1993)
Jerry R. Hobbs, Mark Stickel, Douglas Appelt, and Paul Martin
Interpretation as Abduction Maurizio Atzori
atzori@di.unipi.it
Interpretation as Abduction (1993)
Jerry R. Hobbs, Mark Stickel, Douglas Appelt, and Paul Martin
Summary
Abduction in NLP
The TACITUS Project
The Abductive Commonsense Inference Text Understanding System
Weighted Abduction
Some Local Pragmatics
What is abduction?
B, A B
A Deduction A, A B
B
Induction A(a1), A(a2),..., B(a1), B(a2), B(a3),...
" x . A(x) Þ B(x)
Abduction is inference to the best explanation
Logic as the Language of Thought
The six keys of Cognitive processes
Conjunction of concepts (P Q)
Modus Ponens
Recognition of Obvious Contradictions
Predicate-Argument Relations
We can relate different concept together
Universal Instantiation
In other words: First-order logic!
With no double negations or contrapositives
Nonmonotonic Logic as the Reasoning of Thought
Monotonic logic: KB╞ A Þ KBÈX ╞ A
Nonmonotonic: KB╞ A Þ KBÈX ╞ A
E.g.: negation as failure
KB
bird(x) Ù Øabnormal_bird(x)Þ fly(x)
pinguin(x) Þ abnormal_bird(x)
bird(a)
fly(a) ? true
KB = KB È {pinguin(a)}
fly(a) ? false
Discourse Understanding
People understand discourse because they know so much
How is knowledge used in the interpretation of discourse?
We need to build a KB of commonsense and domain knowledge
Local pragmatics
Reference resolution
Interpretation of compound nominals
Syntactic/lexical ambiguity
Metonymy resolution
Sentence Interpretation
Prove the logical form of the sentence
Together with the constraints that predicates impose on their arguments
Allowing for coercions
Merging redundancies where possible
Making assumptions where necessary
Concrete Example
A cargo train running from Lima to Lorohia was derailed before dawn today after hitting a dynamite charge.
Inspector Eulogio Flores died in the explosion.
The police reported that the incident took place past midnight in the Carahuaichi-Jaurin area.
Incident: Location Peru: Carahuaichi-Jaurin (area)
Incident: Type Bombing
Physical Target: Description “cargo train”
Physical Target: Effect Some damage: “cargo train”
Human Target: Name “Eulogio Flores”
Concrete Example: Inferences
Hitting a dynamite charge = booming
The target = train that hit the charge
The human target = in the explosion
Incident = hitting of the dynamite charge
In order to get the location
TACITUS
Syntactic analysis / Semantic translation component (DIALOGIC)
Obtained mergin a large grammar of English with a semantic translator for all the rules (DIAGRAM Project, Linguistic String Project)
Produce a logical form of the sentence (no KB)
Pragmatic component
Produces an elaborated logical form: inferences, assumptions, coreferences are explicited (KB)
Task component
Outputs the desired answer (e.g. diagnosis or database entries)
Most- or least-specific abduction?
In many AI application, “most-specific abduction” is used
E.g.:
In NLP application:
Sometimes “least-specific abduction” is better
E.g. “fluid”: we don’t want to abduce “lube oil”
Sometimes “most-specific” is better
E.g. “alarm sounded. Flow obstructed” and “the alarm is for the lube oil pressure”: we want to abduce that the flow is of “lube oil”
Weighted Abduction: desiderata
A new abduction scheme (3 features)
Goals should be assumable
Assumption at various levels of specificity
Redundacy of text should be taken into account (yielding more economic proofs)
Weighted Abduction: solution
Every conjunct in the logical form of the sentence is given an assumability cost
If cost(Q)=c then cost(P1) is w1c
If ($...,x,y,...) ...,q(x)20,q(y)10,...
Then ($...,x,...) ...,q(x)10,...
leading to minimality through redundancies
Eg.
Weighted Abduction: examples
Cost(Q1)=$10
Cost(Q2)=$10
How much does it cost to prove Q?
C, or 0.6 if we already know P1 or P2
Q1? Least-specific: $10
Q1 Ù Q2? Most-specific! $18 instead of $20!
Weighted Abduction: “et cetera”
(" x) lube-oil(x) Þ fluid(x)
It is abductively unuseful
“Flow obstructed. Metal particles in lube oil filter”
($ x) lube-oil(x) but we cannot infer fluid(x)
(" x) fluid(x) Þ lube-oil(x)
It “works” but we haven’t such an axiom
It is false!
(" x) fluid(x) Ù etc1(x) Þ lube-oil(x)
etc(x) is something like “abnormal” (special) fluid
It can only be assumed, never proved
Local Pragmatics Phenomena
Definite Reference
I bought a new car last week. The car is already giving me trouble.
I bought a new car last week. The vehicle is already giving me trouble.
I bought a new car last week. The engine is already giving me trouble.
The engine of my new car is already giving me trouble.
KB
(" x) car(x) Þ vehicle(x)
(" x) car(x) Þ ($ x) vehicle(x)
Lexical Ambiguity
John wanted a loan. He went to the bank.
KB
bank1(x) Þ bank(x) “banca”
bank2(x) Þ bank(x) “riva”
loan(y) Þ financial-institution(x) Ù issue(x,y)
financial-institution(x) Ù etc1(x) Þ bank1(x)
river(z) Þ bank2(x) Ù borders(x,z)
Comments