Package org.eclipse.rdf4j.federated.util

Class QueryAlgebraUtil

java.lang.Object

org.eclipse.rdf4j.federated.util.QueryAlgebraUtil

public class QueryAlgebraUtil
extends Object

Various static functions for query handling and parsing (alegbra expression).

Author:

Andreas Schwarte

Constructor Summary

Constructors

Constructor	Description
QueryAlgebraUtil()

Method Summary

Modifier and Type	Method	Description
protected static Var	appendVar(Var var, Set<String> varNames, BindingSet bindings)	Clone the specified variable and attach bindings.
protected static Var	appendVarId(Var var, String varID, Set<String> varNames, BindingSet bindings)	Clone the specified variable and attach bindings, moreover change name of variable by appending "_varId" to it.
protected static Union	constructInnerUnion(StatementPattern stmt, int outerID, Set<String> varNames, List<BindingSet> bindings)
protected static StatementPattern	constructStatement(StatementPattern stmt, Set<String> varNames, BindingSet bindings)	Construct the statement string, i.e.
protected static TupleExpr	constructStatementCheckId(StatementPattern stmt, int varID, Set<String> varNames, BindingSet bindings)	Construct the statement string, i.e.
protected static StatementPattern	constructStatementId(StatementPattern stmt, String varID, Set<String> varNames, BindingSet bindings)	Construct the statement string, i.e.
static Collection<String>	getFreeVars(TupleExpr tupleExpr)	Computes the collection of free variables in the given TupleExpr.
static Value	getVarValue(Var var, BindingSet bindings)	Return the Value of the variable which is either taken from the variable itself (bound) or from the bindingsset (unbound).
static boolean	hasFreeVars(StatementPattern stmt, BindingSet bindings)	returns true iff there is at least one free variable, i.e.
static TupleExpr	selectQuery(ExclusiveGroup group, BindingSet bindings, FilterValueExpr filterExpr, AtomicBoolean evaluated)	Construct a SELECT query for the provided ExclusiveGroup.
static TupleExpr	selectQuery(StatementPattern stmt, BindingSet bindings, FilterValueExpr filterExpr, AtomicBoolean evaluated)	Construct a SELECT query for the provided statement.
static TupleExpr	selectQueryBoundUnion(StatementPattern stmt, List<BindingSet> unionBindings, FilterValueExpr filterExpr, Boolean evaluated)	Construct a SELECT query expression for a bound union.
static TupleExpr	selectQueryStringBoundCheck(StatementPattern stmt, List<BindingSet> unionBindings)	Construct a SELECT query for a grouped bound check.
static Statement	toStatement(StatementPattern stmt)
static Statement	toStatement(StatementPattern stmt, BindingSet bindings)
static StatementPattern	toStatementPattern(Resource subj, IRI pred, Value obj)
static StatementPattern	toStatementPattern(Statement stmt)
static TupleExpr	toTupleExpr(ArbitraryLengthPath node, Set<String> varNames, BindingSet bindings)	Convert the given ArbitraryLengthPath to a fresh TupleExpr where all provided bindings are bound.

Methods inherited from class java.lang.Object

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

Constructor Details

QueryAlgebraUtil

public QueryAlgebraUtil()

Method Details

hasFreeVars

public static boolean hasFreeVars(StatementPattern stmt,
 BindingSet bindings)

returns true iff there is at least one free variable, i.e. there is no binding for any variable

Parameters:

stmt -

bindings -

Returns:

whether there is at least one free variable

getVarValue

public static Value getVarValue(Var var,
 BindingSet bindings)

Return the Value of the variable which is either taken from the variable itself (bound) or from the bindingsset (unbound).

Parameters:

var -

bindings - the bindings, must not be null, use EmptyBindingSet instead

Returns:

the value or null

toTupleExpr

public static TupleExpr toTupleExpr(ArbitraryLengthPath node,
 Set<String> varNames,
 BindingSet bindings)

Convert the given ArbitraryLengthPath to a fresh TupleExpr where all provided bindings are bound.

Parameters:

node -

varNames -

bindings -

Returns:

the fresh and bound expression

toStatementPattern

public static StatementPattern toStatementPattern(Statement stmt)

toStatementPattern

public static StatementPattern toStatementPattern(Resource subj,
 IRI pred,
 Value obj)

toStatement

public static Statement toStatement(StatementPattern stmt)

toStatement

public static Statement toStatement(StatementPattern stmt,
 BindingSet bindings)

selectQuery

public static TupleExpr selectQuery(StatementPattern stmt,
 BindingSet bindings,
 FilterValueExpr filterExpr,
 AtomicBoolean evaluated)
                             throws IllegalQueryException

Construct a SELECT query for the provided statement.

Parameters:

stmt -

bindings -

filterExpr -

evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning

Returns:

the SELECT query

Throws:

IllegalQueryException

selectQuery

public static TupleExpr selectQuery(ExclusiveGroup group,
 BindingSet bindings,
 FilterValueExpr filterExpr,
 AtomicBoolean evaluated)

Construct a SELECT query for the provided ExclusiveGroup. Note that bindings and filterExpr are applied whenever possible.

Parameters:

group - the expression for the query

bindings - the bindings to be applied

filterExpr - a filter expression or null

evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning

Returns:

the SELECT query

selectQueryBoundUnion

public static TupleExpr selectQueryBoundUnion(StatementPattern stmt,
 List<BindingSet> unionBindings,
 FilterValueExpr filterExpr,
 Boolean evaluated)

Construct a SELECT query expression for a bound union.

Pattern:

SELECT ?v_1 ?v_2 ?v_N WHERE { { ?v_1 p o } UNION { ?v_2 p o } UNION ... }

Note that the filterExpr is not evaluated at the moment.

Parameters:

stmt -

unionBindings -

filterExpr -

evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning

Returns:

the SELECT query

selectQueryStringBoundCheck

public static TupleExpr selectQueryStringBoundCheck(StatementPattern stmt,
 List<BindingSet> unionBindings)

Construct a SELECT query for a grouped bound check.

Pattern:

SELECT DISTINCT ?o_1 .. ?o_N WHERE { { s1 p1 ?o_1 FILTER ?o_1=o1 } UNION ... UNION { sN pN ?o_N FILTER ?o_N=oN }}

Parameters:

stmt -

unionBindings -

Returns:

the SELECT query

constructInnerUnion

protected static Union constructInnerUnion(StatementPattern stmt,
 int outerID,
 Set<String> varNames,
 List<BindingSet> bindings)

constructStatement

protected static StatementPattern constructStatement(StatementPattern stmt,
 Set<String> varNames,
 BindingSet bindings)

Construct the statement string, i.e. "s p o . " with bindings inserted wherever possible. Note that the free variables are added to the varNames set for further evaluation.

Parameters:

stmt -

varNames -

bindings -

Returns:

the StatementPattern

constructStatementId

protected static StatementPattern constructStatementId(StatementPattern stmt,
 String varID,
 Set<String> varNames,
 BindingSet bindings)

Construct the statement string, i.e. "s p o . " with bindings inserted wherever possible. Variables are renamed to "var_"+varId to identify query results in bound queries. Note that the free variables are also added to the varNames set for further evaluation.

Parameters:

stmt -

varNames -

bindings -

Returns:

the StatementPattern

constructStatementCheckId

protected static TupleExpr constructStatementCheckId(StatementPattern stmt,
 int varID,
 Set<String> varNames,
 BindingSet bindings)

Construct the statement string, i.e. "s p ?o_varID FILTER ?o_N=o ". This kind of statement pattern is necessary to later on identify available results.

Parameters:

stmt -

varID -

varNames -

bindings -

Returns:

the expression

appendVar

protected static Var appendVar(Var var,
 Set<String> varNames,
 BindingSet bindings)

Clone the specified variable and attach bindings.

Parameters:

var -

varNames -

bindings -

Returns:

the variable

appendVarId

protected static Var appendVarId(Var var,
 String varID,
 Set<String> varNames,
 BindingSet bindings)

Clone the specified variable and attach bindings, moreover change name of variable by appending "_varId" to it.

Parameters:

var -

varID -

varNames -

bindings -

Returns:

the variable

getFreeVars

public static Collection<String> getFreeVars(TupleExpr tupleExpr)

Computes the collection of free variables in the given TupleExpr.

Parameters:

tupleExpr - the expression

Returns:

the free variables

See Also:

• VariableExpr