net.ontopia.topicmaps.query.impl.utils

Class QueryOptimizer

java.lang.Object

net.ontopia.topicmaps.query.impl.utils.QueryOptimizer

public class QueryOptimizer
extends Object

INTERNAL: An optimizer class that knows how to rewrite queries to equivalent, but more efficient queries. Used by the different query processor implementations to improve performance. Note that the only optimizations this class should perform are those which are independent of the tolog implementation used and which only rely on the semantics of tolog.

The only optimizations performed at the moment are:

• Reordering of query clauses for better performance by limiting the number of intermediate results.
• Inlining rules which are simple aliases for a single predicate.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	QueryOptimizer.AbstractQueryOptimizer
static class	QueryOptimizer.AddTypeToRolePlayer INTERNAL:
static class	QueryOptimizer.HierarchyWalker Replaces simple recursive rules with a more efficient custom implementation that just wraps the recursive step.
static class	QueryOptimizer.NextPreviousOptimizer INTERNAL: Optimizes queries that look for the next or the previous value in a sequence from a given start value to not load all values and then do it the hard way, but instead to use a sorted index.
static class	QueryOptimizer.PumpClause
static class	QueryOptimizer.PumpPredicate
static class	QueryOptimizer.RecursivePruner This optimizer adds RemoveDuplicatesPredicate on both sides of recursive calls within predicate rules.
static class	QueryOptimizer.Reorderer INTERNAL: Optimizes the query by reordering the clauses into the optimal order for evaluation.
static class	QueryOptimizer.RuleInliner INTERNAL: Optimizes the query by inlining all rules which are simple aliases for a single predicate.
static class	QueryOptimizer.StringPrefixOptimizer INTERNAL: Optimizes queries that do lookup of occurrences by string value, then filter the string value by a prefix.
static class	QueryOptimizer.TypeConflictResolver Finds cases of conflicting variables and resolves them by replacing predicates which can never succeed with DynamicFailurePredicate.

Constructor Summary

Constructors

Constructor and Description
QueryOptimizer()

Method Summary

Modifier and Type	Method and Description
void	addOptimizer(QueryOptimizerIF optimizer)
static QueryOptimizer	getOptimizer(TologQuery query) INTERNAL: Get hold of an query optimizer instance.
List	optimize(List clauses, QueryContext context)
ParsedRule	optimize(ParsedRule rule)
TologQuery	optimize(TologQuery query)
static List	reorder(List qclauses, Set boundvars, Set literalvars, String rulename, CostEstimator estimator) INTERNAL: Optimizes the order of the query clauses in a context where the given variables are bound.

Methods inherited from class java.lang.Object

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

Constructor Detail

QueryOptimizer

public QueryOptimizer()

Method Detail

getOptimizer

public static QueryOptimizer getOptimizer(TologQuery query)

INTERNAL: Get hold of an query optimizer instance.

Parameters:

query - The parsed query.

addOptimizer

public void addOptimizer(QueryOptimizerIF optimizer)

optimize

public TologQuery optimize(TologQuery query)
                    throws InvalidQueryException

Throws:

InvalidQueryException

optimize

public ParsedRule optimize(ParsedRule rule)
                    throws InvalidQueryException

Throws:

InvalidQueryException

optimize

public List optimize(List clauses,
                     QueryContext context)
              throws InvalidQueryException

Throws:

InvalidQueryException

reorder

public static List reorder(List qclauses,
                           Set boundvars,
                           Set literalvars,
                           String rulename,
                           CostEstimator estimator)

INTERNAL: Optimizes the order of the query clauses in a context where the given variables are bound. Done as a static method so we can use it from within RulePredicate.

Parameters:

qclauses - The list of clauses to be reordered.

boundvars - Contains the variables bound when we get here

literalvars - Contains the variables representing literals. Only an issue in rules.

rulename - The name of the current rule (so we can delay recursive evaluation).