org.projog.core.predicate.udp

Class DynamicUserDefinedPredicateFactory

java.lang.Object

org.projog.core.predicate.udp.DynamicUserDefinedPredicateFactory

All Implemented Interfaces:

PredicateFactory, UserDefinedPredicateFactory

public final class DynamicUserDefinedPredicateFactory
extends Object
implements UserDefinedPredicateFactory

Maintains a record of the clauses that represents a "dynamic" user defined predicate.

A "dynamic" user defined predicate is one that can have clauses added and removed after it has been first defined. This is normally done using the asserta/1, assertz/1 and retract/1 predicates.

See Also:

InterpretedUserDefinedPredicate

Constructor Summary

Constructors

Constructor and Description
DynamicUserDefinedPredicateFactory(KnowledgeBase kb, PredicateKey predicateKey)

Method Summary

Modifier and Type	Method and Description
void	addFirst(ClauseModel clauseModel) Adds a clause to the beginning of the predicate's list of clauses.
void	addLast(ClauseModel clauseModel) Adds a clause to the end of the predicate's list of clauses.
ClauseModel	getClauseModel(int index) Returns the clause at the specified position in this predicate's list of clauses.
Iterator<ClauseModel>	getImplications() Returns an iterator over the clauses of this user defined predicate.
Predicate	getPredicate(Term[] args) Returns a Predicate to be used in the evaluation of a goal.
PredicateKey	getPredicateKey() Returns the key for the predicate this object represents
boolean	isDynamic() Returns true is this predicate is dynamic.
boolean	isRetryable() Should instances of this implementation be re-evaluated when backtracking?

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

DynamicUserDefinedPredicateFactory

public DynamicUserDefinedPredicateFactory(KnowledgeBase kb,
                                          PredicateKey predicateKey)

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()

getPredicateKey

public PredicateKey getPredicateKey()

Description copied from interface: UserDefinedPredicateFactory

Returns the key for the predicate this object represents

Specified by:

getPredicateKey in interface UserDefinedPredicateFactory

Returns:

the key for the predicate this object represents

isDynamic

public boolean isDynamic()

Description copied from interface: UserDefinedPredicateFactory

Returns true is this predicate is dynamic.

A "dynamic" predicate is a user defined predicate that can have clauses added or removed after is first defined.

Specified by:

isDynamic in interface UserDefinedPredicateFactory

Returns:

true is this predicate is dynamic

getImplications

public Iterator<ClauseModel> getImplications()

Returns an iterator over the clauses of this user defined predicate.

The iterator returned will have the following characteristics:

• Calls to Iterator.next() return a new copy of the ClauseModel to avoid the original being altered.
• Calls to Iterator.remove() do alter the underlying structure of this user defined predicate.

Specified by:

getImplications in interface UserDefinedPredicateFactory

Returns:

an iterator over the clauses in the predicate in proper sequence.

addFirst

public void addFirst(ClauseModel clauseModel)

Description copied from interface: UserDefinedPredicateFactory

Adds a clause to the beginning of the predicate's list of clauses.

Specified by:

addFirst in interface UserDefinedPredicateFactory

Parameters:

clauseModel - the clause to add to the beginning of the predicate

addLast

public void addLast(ClauseModel clauseModel)

Description copied from interface: UserDefinedPredicateFactory

Adds a clause to the end of the predicate's list of clauses.

Specified by:

addLast in interface UserDefinedPredicateFactory

Parameters:

clauseModel - the clause to add to the end of the predicate

getClauseModel

public ClauseModel getClauseModel(int index)

Description copied from interface: UserDefinedPredicateFactory

Returns the clause at the specified position in this predicate's list of clauses.

Specified by:

getClauseModel in interface UserDefinedPredicateFactory

Parameters:

index - index of the clause to return

Returns:

the clause at the specified position in this predicate's list of clauses or null if out of bounds

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