Class LegacyBacktrackEvaluator.BacktrackIterator

java.lang.Object

fr.inria.rules.integraal.query_evaluation.conjunction.backtrack.legacy.LegacyBacktrackEvaluator.BacktrackIterator

All Implemented Interfaces:

Iterator<Substitution>

Enclosing class:

LegacyBacktrackEvaluator<QD extends QueryableData>

protected class LegacyBacktrackEvaluator.BacktrackIterator
extends Object
implements Iterator<Substitution>

The BacktrackIterator is used to redefine the iterator return as an answer to the query. It computes results only when needed. Calling hasNext() effectively computes the next answer.

Field Summary

Fields

Modifier and Type	Field	Description
protected boolean	backtrack	Indicates whether the iterator is currently backtracking.
protected final FOQueryEvaluator<FOFormula, QD>	evaluator	Query evaluator used to evaluate the sub-queries
protected boolean	hasCurrentSolution	Indicates whether the current solution has already been computed.
protected final Set<Variable>	joinVariables	Variables shared by several sub-queries and therefore used for joins.
protected int	level	Current level in the backtracking search tree.
protected final Substitution	preHomomorphism	Pre-existing substitution that every answer must extend.
protected final FOQuery<? extends FOFormulaConjunction>	query	Query to evaluate
protected final QD	queryableData	The queryableData on which to evaluate the query
protected final Scheduler	scheduler	Object used to choose the next sub-query to evaluate
protected SolutionManager	solutionManager	Object used to handle the results to the query.
protected final Collection<Variable>	vars	Variables requested in the final answer.

Constructor Summary

Constructors

Constructor	Description
BacktrackIterator(FOQueryEvaluator<FOFormula, QD> evaluator, FOQuery<? extends FOFormulaConjunction> query, QD queryableData, Collection<Variable> vars, Substitution preHomomorphism)	Creates a backtracking iterator for one conjunctive query evaluation.

Method Summary

Modifier and Type	Method	Description
protected void	computeNextLevel()	Compute and update the next level
protected void	computePreviousLevel()	Compute and update the previous level
protected void	fail()	Called when there is a failure during the backtrack algorithm.
boolean	hasNext()	/////////////////
Substitution	next()
protected boolean	solutionFound()	Indicates whether a full solution has been found.
protected void	success()	Called when there is a success during the backtrack algorithm.

Methods inherited from class Object

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

Methods inherited from interface Iterator

forEachRemaining, remove

Field Details

evaluator

protected final FOQueryEvaluator<FOFormula, QD extends QueryableData> evaluator

Query evaluator used to evaluate the sub-queries

query

protected final FOQuery<? extends FOFormulaConjunction> query

Query to evaluate

queryableData

protected final QD extends QueryableData queryableData

The queryableData on which to evaluate the query

scheduler

protected final Scheduler scheduler

Object used to choose the next sub-query to evaluate

joinVariables

protected final Set<Variable> joinVariables

Variables shared by several sub-queries and therefore used for joins.

vars

protected final Collection<Variable> vars

Variables requested in the final answer.

preHomomorphism

protected final Substitution preHomomorphism

Pre-existing substitution that every answer must extend.

solutionManager

protected SolutionManager solutionManager

Object used to handle the results to the query. It is used as a sort of cache during the query evaluation

hasCurrentSolution

protected boolean hasCurrentSolution

Indicates whether the current solution has already been computed.

level

protected int level

Current level in the backtracking search tree.

backtrack

protected boolean backtrack

Indicates whether the iterator is currently backtracking.

Constructor Details

BacktrackIterator

public BacktrackIterator(FOQueryEvaluator<FOFormula, QD> evaluator,
 FOQuery<? extends FOFormulaConjunction> query,
 QD queryableData,
 Collection<Variable> vars,
 Substitution preHomomorphism)

Creates a backtracking iterator for one conjunctive query evaluation.

Parameters:

evaluator - the evaluator used for sub-queries

query - the query to evaluate

queryableData - the data source being queried

vars - the variables to project in the answers

preHomomorphism - the substitution that answers must extend

Method Details

hasNext

public boolean hasNext()

/////////////////

Specified by:

hasNext in interface Iterator<Substitution>

next

public Substitution next()

Specified by:

next in interface Iterator<Substitution>

success

protected void success()

Called when there is a success during the backtrack algorithm. A success is when a sub-query is evaluated and correct in regard to the previously computed answer.

fail

protected void fail()

Called when there is a failure during the backtrack algorithm. A failure is when a sub-query is evaluated and is incorrect in regard to the previously computed answer. A failure is also considered if the answer is found to be able to go to the next result if we want all the result of the query

computePreviousLevel

protected void computePreviousLevel()

Compute and update the previous level

computeNextLevel

protected void computeNextLevel()

Compute and update the next level

solutionFound

protected boolean solutionFound()

Indicates whether a full solution has been found.

Returns:

true iff a solution is found