org.projog.core.predicate

Class UnknownPredicate

java.lang.Object

org.projog.core.predicate.UnknownPredicate

All Implemented Interfaces:

PredicateFactory, PreprocessablePredicateFactory

public final class UnknownPredicate
extends 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)

Constructor Summary

Constructors

Constructor and Description
UnknownPredicate(KnowledgeBase kb, PredicateKey key)

Method Summary

Modifier and Type	Method and Description
Predicate	getPredicate(Term[] args) Returns a Predicate to be used in the evaluation of a goal.
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

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

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