Package org.projog.core.predicate

Class UnknownPredicate

java.lang.Object

org.projog.core.predicate.UnknownPredicate

All Implemented Interfaces:

PredicateFactory, PreprocessablePredicateFactory

public final class UnknownPredicate
extends java.lang.Object
implements PreprocessablePredicateFactory

Represents all predicates that a KnowledgeBase has no definition of.

Always fails to evaluate successfully.

See Also:

Predicates.getPredicateFactory(PredicateKey), Predicates.getPredicateFactory(Term)

Field Summary

Fields

Modifier and Type	Field	Description
private PredicateFactory	actualPredicateFactory
private KnowledgeBase	kb
private PredicateKey	key

Constructor Summary

Constructors

Constructor	Description
UnknownPredicate(KnowledgeBase kb, PredicateKey key)

Method Summary

Modifier and Type	Method	Description
Predicate	getPredicate(Term[] args)	Returns a Predicate to be used in the evaluation of a goal.
private void	instantiatePredicateFactory()
boolean	isRetryable()	Should instances of this implementation be re-evaluated when backtracking?
PredicateFactory	preprocess(Term arg)

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.projog.core.predicate.PredicateFactory

isAlwaysCutOnBacktrack

Field Detail

kb

private final KnowledgeBase kb

key

private final PredicateKey key

actualPredicateFactory

private PredicateFactory actualPredicateFactory

Constructor Detail

UnknownPredicate

public UnknownPredicate(KnowledgeBase kb,
                        PredicateKey key)

Method Detail

getPredicate

public Predicate getPredicate(Term[] args)

Description copied from interface: PredicateFactory

Returns a Predicate to be used in the evaluation of a goal.

Specified by:

getPredicate in interface PredicateFactory

Parameters:

args - the arguments to use in the evaluation of the goal

Returns:

Predicate to be used in the evaluation of the goal

See Also:

Predicate.evaluate()

preprocess

public PredicateFactory preprocess(Term arg)

Specified by:

preprocess in interface PreprocessablePredicateFactory

instantiatePredicateFactory

private void instantiatePredicateFactory()

isRetryable

public boolean isRetryable()

Description copied from interface: PredicateFactory

Should instances of this implementation be re-evaluated when backtracking?

Some goals (e.g. X is 1) are only meant to be evaluated once (the statement is either true or false) while others (e.g. repeat(3)) are meant to be evaluated multiple times. For instances of Predicate that are designed to possibly have Predicate.evaluate() called on them multiple times for the same individual query this method should return true. For instances of Predicate that are designed to only be evaluated once per individual query this method should return false.

Specified by:

isRetryable in interface PredicateFactory

Returns:

true if an attempt should be made to re-evaluate instances of implementing classes when backtracking, false otherwise