Deduction Meeting 2008
LogAnswer
Deduction-Based Question-Answering
Hermann Helbig, Ingo Glöckner
Björn Pelzer (AGKI)
Ulrich Furbach, Björn Pelzer
LogAnswer
1/11
The Problem: Open-Domain Question-Answering:
A question-answering-system
• finds textual answers
• to natural-language questions
regarding arbitrary topics.
Example:
"Who was the lead singer of Nirvana?"
 Kurt Cobain.
Advantages of QA compared to conventional search
engines:
• time savings: answers instead of documents
• space savings: answers fit onto small displays
Björn Pelzer (AGKI)
LogAnswer
2/11
Specifically: Deduction-Based QA
Existing QA-systems are (mostly) syntax-based:
• shallow linguistic methods like string comparisons
• database queries
The peak of Mount
Everest is 8848 metres
above sea level.
QA-system
How tall is
Mt. Everest?
?
Problems:
• no semantics available to the system
• no matching strings or strings too far apart  no answer
• can be made robust, but answer quality degrades
Björn Pelzer (AGKI)
LogAnswer
3/11
Specifically: Deduction-Based QA
LogAnswer uses a logic-based knowledge-representation.
The peak of Mount
Everest is 8848 metres
above sea level.
How tall is
Mt. Everest?
QA-system
(...)
peak(P, M) 
dist(P, SL, D)
 height(M, D)
(...)
8848 metres
• logical rules express semantics - "world knowledge"
• answers can be inferred using multiple sources
Björn Pelzer (AGKI)
LogAnswer
4/11
LogAnswer - Overview
The LogAnswer-project combines...
natural language
processing
deduction
• robust linguistic methods • precise inferencing
• lack of precision
• full FOL expressivity
• brittle
• NLP-components
• E-KRHyper theorem
• MultiNet knowledge-base prover
– newspaper-corpus
– Wikipedia
– circa 2.5 million sentences
Björn Pelzer (AGKI)
LogAnswer
5/11
LogAnswer - Prototype Architecture
LogAnswer web interface
question
answer
NL-question
analysis
answer
composition
robust deduction
control
logical query
logical answer
facts
query +
deduction
candidate
results
theorem prover
E-KRHyper
answer
candidates
pre-analyzed
text corpus
Björn Pelzer (AGKI)
background
knowledge
LogAnswer
6/11
LogAnswer - Prototype Architecture - Theorem Prover
E-KRHyper:
• Knowledge Representation Hypertableau theorem
prover for full first-order logic with Equality
• support for TPTP-input
• operates as reasoning server:
- general background knowledge is entered once
- query-specific clauses are entered and retracted as
needed
Björn Pelzer (AGKI)
LogAnswer
7/11
LogAnswer - Robust Deduction
A query is represented as a conjunction of literals.
Wie viele Menschen starben beim Untergang der Estonia?
(= How many people died in the sinking of the Estonia?)
sub(X1, estonia.1.1)  attch(X1, X2)  subs(X2, untergang.1.1)
 subs(X3, sterben.1.1)  circ(X3, X2)  aff(X3, ANSWER) 
pred(ANSWER, mensch.1.1)
Problem:
Logic is too precise. The query is too demanding for a
knowledge base derived from imperfect textual sources:
 The answer is there, but we don't find it.
Björn Pelzer (AGKI)
LogAnswer
8/11
LogAnswer - Robust Deduction
Solution: Query Relaxation
• The prover informs LogAnswer how far the proof has
progressed and for which query literals it fails.
• LogAnswer selects the most successful partial proof, drops
the failed literal from the query and restarts the prover.
sub(X1, estonia.1.1)  attch(X1, X2)  subs(X2, untergang.1.1)
 subs(X3, sterben.1.1)  circ(X3, X2)  aff(X3, ANSWER) 
pred(ANSWER, mensch.1.1)
 ANSWER = 852 (2 relaxations)
• Answer candidates are ranked according to the number
of relaxations required for a proof (and other criteria).
• The best answers are selected and returned to the user.
Björn Pelzer (AGKI)
LogAnswer
9/11
LogAnswer - Example
Question: In welchem Land liegt der Kilimandscharo?
(= What country is the Kilimanjaro located in?)
answer: Tansania
quality: 39%
passage: 1893 begann die Arbeit am Kilimandscharo in Tansania .
document: Leipziger_Missionswerk.239
answer: Arusha
quality: 14%
passage: Er liegt im Nordosten nördlich von Arusha und nahe der kenianischen
Grenze zwischen dem Mount Meru und dem Kilimandscharo und ist über den
internationalen Flughafen Kilimanjaro bei Arusha erreichbar .
document: Arusha-Nationalpark.90
answer: Afrika
quality: 13%
passage: Schnee auf dem Kilimandscharo ) , 1936 - Kurzgeschichte aus Afrika To
have and have not ( dt .
document: Ernest_Hemingway.4638
Björn Pelzer (AGKI)
LogAnswer
10/11
LogAnswer can be tested at
www.loganswer.de
Thanks, see you at the poster!
Björn Pelzer (AGKI)
LogAnswer
11/11