com.bigdata.rdf.sparql.ast.optimizers

Class ASTStaticBindingsOptimizer.VariableUsageInfo

java.lang.Object

com.bigdata.rdf.sparql.ast.optimizers.ASTStaticBindingsOptimizer.VariableUsageInfo

Enclosing class:

ASTStaticBindingsOptimizer

public static class ASTStaticBindingsOptimizer.VariableUsageInfo
extends Object

Helper class used to record usage of a given variable, i.e. linking variables to constructs in which they occur.

Constructor Summary

Constructors

Constructor and Description
ASTStaticBindingsOptimizer.VariableUsageInfo() Constructor creating an empty object (no usages).

Method Summary

Methods

Modifier and Type	Method and Description
void	extractVarSPUsageInfoChildren(GroupNodeBase<?> group) Extracts usage information for the variable from statement patterns being direct children of the current node (ignoring the node itself).
void	extractVarSPUsageInfoChildrenOrSelf(GroupNodeBase<?> group) Extracts usage information for the variable inside statement patterns from the current node itself and its children (recursively).
void	extractVarUsageInfoSelf(GroupNodeBase<?> group) Extracts variable usage information (variables and the nodes they occur in), investigating FILTERs, assignment nodes, and statement pattern nodes, but /not/ recursing into children.
Map<IVariable<?>,List<IQueryNode>>	getUsageMap() Gets the map recoding all usages of all variables (internal data structure maintained by the class).
List<IQueryNode>	getVarUsages(IVariable<?> var) Returns the list of variable usages.
static ASTStaticBindingsOptimizer.VariableUsageInfo	merge(ASTStaticBindingsOptimizer.VariableUsageInfo x, ASTStaticBindingsOptimizer.VariableUsageInfo y) Merges two ASTStaticBindingsOptimizer.VariableUsageInfo, creating a new one containing the merged information.
boolean	varUsed(IVariable<?> var) Returns true iff usage records for the var are available.
boolean	varUsedInFilterOrAssignment(IVariable<?> var) Returns true if a usage record for the given variable inside a FILTER or BIND/VALUES node has been recorded.

Methods inherited from class java.lang.Object

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

Constructor Detail

ASTStaticBindingsOptimizer.VariableUsageInfo

public ASTStaticBindingsOptimizer.VariableUsageInfo()

Constructor creating an empty object (no usages).

Method Detail

varUsedInFilterOrAssignment

public boolean varUsedInFilterOrAssignment(IVariable<?> var)

Returns true if a usage record for the given variable inside a FILTER or BIND/VALUES node has been recorded. The rationale of this check is as follows: if a variable used inside a static binding is queries in such an ancestor filter, the binding must not be considered global. As an example, consider the following query:

 SELECT * WHERE {
    FILTER(!bound(?x))
    {
      BIND(1 AS ?x)
    }
  } 
 
 Expected result is the empty set, according to bottom-up semantics.
 We must *not* rewrite this query as 
 
 SELECT * WHERE {
   FILTER(!bound(?x))
  } VALUES ?x { 1 }
  
 The reason is that in this case the FILTER will pass, while ?x in the
 original query the BIND(1 AS ?x) is in scope and the filter fails.
  
 The same holds for queries where the FILTER is at the same level
 as the BIND/VALUES clause, such as:
 
 SELECT * WHERE {
    FILTER(!bound(?x))
    {
      BIND(1 AS ?x)
    }
  }

Parameters:

var -

Returns:

varUsed

public boolean varUsed(IVariable<?> var)

Returns true iff usage records for the var are available.

Parameters:

var -

Returns:

getVarUsages

public List<IQueryNode> getVarUsages(IVariable<?> var)

Returns the list of variable usages.

Parameters:

var -

Returns:

getUsageMap

public Map<IVariable<?>,List<IQueryNode>> getUsageMap()

Gets the map recoding all usages of all variables (internal data structure maintained by the class).

Returns:

extractVarUsageInfoSelf

public void extractVarUsageInfoSelf(GroupNodeBase<?> group)

Extracts variable usage information (variables and the nodes they occur in), investigating FILTERs, assignment nodes, and statement pattern nodes, but /not/ recursing into children.

Parameters:

group - the group where to extract filter var info (non-recursively)

extractVarSPUsageInfoChildren

public void extractVarSPUsageInfoChildren(GroupNodeBase<?> group)

Extracts usage information for the variable from statement patterns being direct children of the current node (ignoring the node itself).

Parameters:

group - the group node base in which we perform the lookup

extractVarSPUsageInfoChildrenOrSelf

public void extractVarSPUsageInfoChildrenOrSelf(GroupNodeBase<?> group)

Extracts usage information for the variable inside statement patterns from the current node itself and its children (recursively). Note that we do not report variable usage in filters, as those might be not in scope and inlining is not safe (interference with ASTBottomUpOptimizer.handleFiltersWithVariablesNotInScope(com.bigdata.rdf.sparql.ast.eval.AST2BOpContext, com.bigdata.rdf.sparql.ast.StaticAnalysis, com.bigdata.rdf.sparql.ast.QueryBase, com.bigdata.bop.IBindingSet[]))!). This maybe somewhat too strict (leading to situations where we do not inline static variable bindings), but is safe.

Parameters:

group -

merge

public static ASTStaticBindingsOptimizer.VariableUsageInfo merge(ASTStaticBindingsOptimizer.VariableUsageInfo x,
                                                 ASTStaticBindingsOptimizer.VariableUsageInfo y)

Merges two ASTStaticBindingsOptimizer.VariableUsageInfo, creating a new one containing the merged information. The original objects are not modified.