Answering complex questions and performing deep reasoning in advance question answering systems Chitta Baral 1, Michael Gelfond 2 and Richard Scherl 3 1 Arizona State University, AZ. 2 Texas Tech University, TX. 3 Monmouth University, NJ.

QUERIES Prediction, explanation, planning, cause, counterfactual, etc.

Queries and Answers Answering queries with respect to databases: various query languages – Relational databases: SQL3 – Object-Oriented Databases: OQL – Web databases, XML Databases: XML-QL – Prolog queries Natural language queries – Often translated to one of the above Complex Queries! – Need knowledge beyond that is present in the given data (or text) to answer. – Need reasoning mechanisms that can not be expressed in standard database query languages or classical logics.

Complex Query example – predictive query Text/Data: John is at home in Boston and has not bought a ticket to Paris yet. Query: – What happens if John tries to fly to Paris? – What happens if John buys a ticket to Paris and then tries to fly to Paris? Missing knowledge: – When can one fly? – What is the result of flying?

Complex Query example: explanation query Text/Data: On Dec 10 th John is at home in Boston and does not have a ticket to Paris yet. On Dec 11 th he is in Paris. Query: – Explain what might have happened in between. Bought a ticket; gone to the Boston airport; taken a flight to Paris.

Complex Query Example: planning query Text/Data: On Dec 10 th John is at home in Boston and does not have a ticket to Paris yet. Query: What does John need to do to be in Paris on Dec 11 th. – He needs to buy the ticket || get to the airport; fly to Paris.

Complex Query Example: Counterfactual Query Text/Data: On Dec 10 th John is at home in Boston. He made a plan to get to Paris by Dec 11 th. He then bought a ticket. But on his way to the airport he got stuck in the traffic. He did not make it to the flight. Query: What if John had not gotten stuck in the traffic?

Complex Query Example: query about narratives Text/Data: John, who always carries his laptop with him, took a flight from Boston to Paris on the morning of Dec 11 th. Queries: – Where is John on the evening of Dec 11 th ? – In which city is John’s laptop that evening?

Complex Query Example: Causal queries Text/Data: On Dec 10 th John is at home in Boston. He made a plan to get to Paris by Dec 11 th. He then bought a ticket. But on his way to the airport he got stuck in the traffic. He reached the airport late and his flight had left. Queries: – What are the causes of John missing the flight?

Complex Query Example: Unusual behavior John flew from Boston to Paris. He did not check in any luggage in Boston. When he got out of the plane in CDG he did not have anything in his hand. Was there anything unusual about John’s behavior when he checked in? – Need information on normal behavior of people who check in for an international flight – Normal inertia with respect to hand luggage (from checking in to getting out of the plane)

Our approach to answer such queries Develop various knowledge modules in an appropriate knowledge representation and reasoning language. – Travel module (includes flying, driving) – Geography Module – Time module – Reasoning about actions module – Planning module – Explanation module – Counterfactual module – Cause finding module – Most of the above modules with defaults and exceptions.

Knowledge Representation and Reasoning: AnsProlog

What properties should an appropriate KR & R language have Should be non-monotonic. So that the system can revise its earlier conclusion in light of new information. Should have the ability to represent normative statements, exceptions, and default statements, and should be able to reason with them. Should be expressive enough to express and answer problem solving queries such as planning queries, counterfactual queries, explanation queries and diagnostic queries. Should have a simple and intuitive syntax so that domain experts (who may be non-computer scientists) can express knowledge using it. Should have enough existing research (or building block results) about this language so that one does not have to start from scratch. Should have interpreters or implementation of the language so that one can indeed represent and reason in this language. (I.e., it should not be just a theoretical language.) Should have existing applications that have been built on this language so as to demonstrate the feasibility that applications can be indeed built using this language.

AnsProlog – a suitable knowledge representation language AnsProlog – Programming in logic with answer sets – Language (and semantics) was first introduced in the paper ``The Stable Model Semantics For Logic Programming - Gelfond, Lifschitz (1988)’’, among the most cited source documents in the CiteSeer database. Stable Model Semantics For Logic Programming - Gelfond, Lifschitz (1988) Syntax: Set of statements of the form: A 0 or … or A k  B 1, …, B m, not C 1, … not C n. Intuitive meaning of the above statement: – If B 1, …, B m is known to be true and C 1, …, C n can be assumed to be false then at least one of A 0,…, A k must be true. It satisfies all the properties mentioned in the previous slide (and much more)! – Details in my Book ``Knowledge Representation, Reasoning and Declarative Problem Solving’’. Cambridge University Press, 2003.

AnsProlog vs Prolog Differences: – Prolog is sensitive to ordering of rules and ordering of literals in the body of rules. – Inappropriate ordering leads to infinite loops. (Thus Prolog is not declarative; hence not a knowledge representation language) – Prolog stumbles with recursion through negation – No disjunction in the head (less power) Similarities: For certain subclasses of AnsProlog Prolog can be thought of as a top-down engine.

AnsProlog vs other KR & R languages AnsProlog has a simple syntax and semantics Syntax has structure that allows defining sub-classes More expressive than propositional and first-order logic; propositional AnsProlog is as expressive as default logic. Yet much simpler. It has a very large body of support structure (theoretical results as well as implementations) among the various knowledge representation languages – Description logic comes close. But its focus is somewhat narrow, mostly to represent and reason about ontologies. …

Illustration of Complex Question Answering John flying to Baghdad to meet Bob example.

The extracted text and the queries Extracted Text – John spent Dec 10 in Paris and took a plane to Baghdad the next morning. He was planning to meet Bob who was waiting for him there. Queries – Q 1 : Was John in the Middle East in mid- December? – Q 2 : If so, did he meet Bob in the Middle East in mid-December?

Required background and common- sense knowledge Knowledge about geographical objects and their hierarchy. (M1) – Baghdad is a city in Iraq. Iraq is a country in the middle east region. … – A city in a country in a region is a city in that region. Knowledge about travel events. (M2) – If someone is in a city then she is in the country where the city is in and so on. – Executability conditions and effect of travel events – Inertia – Duration of flying Knowledge about time units. (M3) – Relation between various time granularities Knowledge about planned events, meeting events. (M4) – People normally follow through their plans – Executability condition of meeting events

M 1 : The geography Module List of places – is(baghdad,city). – is(iraq,country). –... Relation between places – in(baghdad, iraq). – in(iraq,middle_east). – in(paris,france). – in(france,western_europe). – in(western_europe,europe). –... Transitive closure in(P1,P3)  in(P1,P2), in(P2,P3). Completeness assumption about `in’ -in(P1,P2)  not in(P1,P2)

M 2 : The traveling module Based on theory of dynamic systems – Views world as a transition diagram States are labeled by fluents Arcs labeled by actions Various types of traveling events – instance_of(fly,travel). – instance_of(drive,travel). … Generic description of John flying to Baghdad – event(a1). – type(a1,fly). – actor(a1,john). – destination(a1,baghdad). Actual event is recorded as – occurs(a1,i)

M 2 : The traveling module (cont.) Representation of transition Diagram – State Constraints loc(P2,X,T)  loc(P1,X,T), in(P2,P1). disjoint(P1,P2)  -in(P1,P2), -in(P2,P1), neq(P1,P2). -loc(P2,X,T)  loc(P1,X,T),disjoint(P1,P2). – Causal Laws loc(P,X,T+1)  occurs(E,T), type(E,travel), actor(E,X), destination(E,P), -interference(E,T). -interference(E,T)  not interference(E,T). – Executability Conditions -occurs(E,T)  cond(T). – Inertia Rules (frame axioms) loc(P,X,T+1)  loc(P,X,T), not -loc(P,X,T+1). -loc(P,X,T+1)  -loc(P,X,T), not loc(P,X,T+1).

Reasoning with M1 and M2 Given – loc(paris,john,0). – loc(baghdad,bob,0). – occurs(a1,0). And with M 1 and M 2 AnsProlog can conclude – loc(baghdad,john,1), loc(baghdad,bob,1), – loc(middle_east,john,1), -loc(paris,john,1)

M 3 : Time and durations Duration of actions (additional ones needed for month etc.) time(T+1,day,D)  occurs(E,T), type(E,fly), time(T,day,D), not -time(T+1,day,D). Basic measuring units – day(1..31). month(1..12). part(start). part(end). part(middle). Rules translating between one granularity to another time(T,part,middle)  time(T,d,D), 10 < D < 20. time(T,season,summer)  time(T,month,M), 5 < M < 9. Missing elements from the module – next(date(10,12,03),date(11,12,03)). – next(date(31,12,03),date(1,1,04)).

Reasoning with M 1, M 2 and M 3 Given information about John’s flight – loc(paris,john,0). – loc(baghdad,bob,0). – occurs(a1,0). – time(0,day,11). – time(0,month,12). The query Q1 – ? loc(middle_east,john,T), time(T,month,12), time(T,part,middle). AnsProlog gives the correct answer: yes with T = 1.

M 4 : planning to meet and meeting Describing the event meet – event(a2). type(a2,meet). – actor(a2,john). actor(a2,bob). – place(a2,baghdad). Executability conditions of the meeting event -occurs(E,T)  type(E,meet), actor(E,X), place(E,P), -loc(P,X,T). Planned meeting: planned(a2,1). Planned actions and their occurrence: ``People normally follow their plans’’ occurs(E,T)  planned(E,T), not -occurs(E). People persist with their plans until it happens planned(E,T+1)  planned(E,T), -occurs(E,T). Second query – ? occurs(E,T), type(E,meet), actor(E,john), actor(E,bob), loc(middle_east,john,T), time(T,month,12), time(T,part,middle). Answer: Yes.

Conclusion Answering complex queries need a lot of knowledge and reasoning rules that are not present in the text or data. These reasoning rules and knowledge need to be encoded as modules in an appropriate knowledge representation and reasoning language.

Ongoing and Future Work Further development of Modules (examples) – Travel duration – Time period representation issues (eg. time zones) – Dealing with the case when a planned event fails Further development of the AnsProlog language – Not good when dealing with time or similar features that result in large instantiations. Taking advantage of Prolog execution engine when necessary – Necessity of set notations, aggregates etc.

Acknowledgements Steve Maiorano, Jean-Michel Pomarede Ryan Weddle, Jicheng Zhao, Saadat Anwar, Luis Tari (all from ASU), Greg Gelfond (from Texas Tech University)