net.sf.tweety.logics.cl

Class CReasoner

java.lang.Object

net.sf.tweety.commons.Reasoner

net.sf.tweety.logics.cl.CReasoner

public class CReasoner
extends Reasoner

This class models a c-reasoner for conditional logic. Reasoning is performed by computing a minimal c-representation for the given knowledge base.
A c-representation for a conditional knowledge base R={r1,...,rn} is a ranking function k such that k accepts every conditional in R (k |= R) and if there are numbers k0,k1+,k1-,...,kn+,kn- with
k(w)=k0 + \sum_{w verifies ri} ki+ + \sum_{w falsifies ri} kj- for every w. A c-representation is minimal if k0+...+kn- is minimal. This reasoner uses mathematical optimization for solving the above problem and is usually faster than the brute force approach.

See Gabriele Kern-Isberner. Conditionals in nonmonotonic reasoning and belief revision. Lecture Notes in Computer Science, Volume 2087. 2001.

Author:

Matthias Thimm

Field Summary

Fields

Modifier and Type	Field and Description
private RankingFunction	crepresentation The c-representation for this knowledge base.

Constructor Summary

Constructors

Constructor and Description
CReasoner(BeliefBase beliefBase) Creates a new c-representation reasoner for the given knowledge base.

Method Summary

Modifier and Type	Method and Description
private RankingFunction	computeCRepresentation() Computes a minimal c-representation for this reasoner's knowledge base.
private Statement	getAcceptanceConstraint(Conditional cond, java.util.Map<PossibleWorld,IntegerVariable> ranks) For the given conditional (B|A) and the given ranks of possible worlds, this method constructs the inequation k(AB) < k(A-B) where k(AB) is the minimum of the ranks of the interpretations that satisfy AB.
RankingFunction	getCRepresentation() Returns the c-representation this reasoner bases on.
private Statement	getRankConstraint(PossibleWorld w, IntegerVariable ranki, java.util.Map<Conditional,IntegerVariable> kappa_pos, java.util.Map<Conditional,IntegerVariable> kappa_neg) For the given interpretation "i" and the given kappas, this method computes the constraint k("i")=\sum_{"i" verifies ri} ki+ + \sum_{"i" falsifies ri} kj-
Answer	query(Formula query) This method determines the answer of the given query wrt.

Methods inherited from class net.sf.tweety.commons.Reasoner

getKnowledgeBase

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

crepresentation

private RankingFunction crepresentation

The c-representation for this knowledge base. Once this ranking function has been computed it is used for subsequent queries in order to avoid unnecessary computations.

Constructor Detail

CReasoner

public CReasoner(BeliefBase beliefBase)

Creates a new c-representation reasoner for the given knowledge base.

Parameters:

beliefBase - a knowledge base.

Method Detail

query

public Answer query(Formula query)

Description copied from class: Reasoner

This method determines the answer of the given query wrt. to the given knowledge base.

Specified by:

query in class Reasoner

Parameters:

query - a query.

Returns:

the answer to the query.

getCRepresentation

public RankingFunction getCRepresentation()

Returns the c-representation this reasoner bases on.

Returns:

the c-representation this reasoner bases on.

computeCRepresentation

private RankingFunction computeCRepresentation()

Computes a minimal c-representation for this reasoner's knowledge base.

Returns:

a minimal c-representation for this reasoner's knowledge base.

getAcceptanceConstraint

private Statement getAcceptanceConstraint(Conditional cond,
                                          java.util.Map<PossibleWorld,IntegerVariable> ranks)

For the given conditional (B|A) and the given ranks of possible worlds, this method constructs the inequation k(AB) < k(A-B) where k(AB) is the minimum of the ranks of the interpretations that satisfy AB.

Parameters:

cond - a conditional

ranks - a map from possible worlds to integer variables

Returns:

an inequation representing the acceptance of the conditional

getRankConstraint

private Statement getRankConstraint(PossibleWorld w,
                                    IntegerVariable ranki,
                                    java.util.Map<Conditional,IntegerVariable> kappa_pos,
                                    java.util.Map<Conditional,IntegerVariable> kappa_neg)

For the given interpretation "i" and the given kappas, this method computes the constraint
k("i")=\sum_{"i" verifies ri} ki+ + \sum_{"i" falsifies ri} kj-

Parameters:

i - a possible world.

ranki - the rank (an integer variable) of interpretation "i".

kappa_pos - the positive penalties for interpretations.

kappa_min - the negative penalties for interpretations.