Package org.apache.jena.sparql.expr

Class ExprLib

java.lang.Object

org.apache.jena.sparql.expr.ExprLib

public class ExprLib
extends java.lang.Object

Constructor Summary

Constructors

Constructor	Description
ExprLib()

Method Summary

Modifier and Type	Method	Description
static NodeValue	evalOrNull(Expr expr, Binding binding, FunctionEnv functionEnv)	Evaluate or return null.
static Expr	foldConstants(Expr expr)	Attempt to fold any sub-expressions of the Expr.
static boolean	isAssignmentSafeEquality(Expr expr)	Decide whether an expression is safe for using a graph substitution.
static boolean	isAssignmentSafeEquality(Expr expr, boolean graphHasStringEquality, boolean graphHasNumercialValueEquality)
static boolean	isStable(Expr expr)	Some "functions" are non-deterministic (unstable) - calling them with the same arguments does not yields the same answer each time.
static Expr	nodeToExpr(Node n)	Go from a node to an expression.
static Expr	replaceAggregateByVariable(Expr expr)	transform an expression that may involve aggregates into one that just uses the variable for the aggregate
static Expr	rewriteTriple(Triple t)

Methods inherited from class java.lang.Object

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

Constructor Detail

ExprLib

public ExprLib()

Method Detail

evalOrNull

public static NodeValue evalOrNull(Expr expr,
                                   Binding binding,
                                   FunctionEnv functionEnv)

Evaluate or return null.

This is better (faster) than the simple implementation which captures ExprEvalException and returns null.

foldConstants

public static Expr foldConstants(Expr expr)

Attempt to fold any sub-expressions of the Expr. Return an expression that is equivalent to the argument but maybe simpler.

Parameters:

expr -

Returns:

Expression

replaceAggregateByVariable

public static Expr replaceAggregateByVariable(Expr expr)

transform an expression that may involve aggregates into one that just uses the variable for the aggregate

isAssignmentSafeEquality

public static boolean isAssignmentSafeEquality(Expr expr)

Decide whether an expression is safe for using a graph substitution. Need to be careful about value-like tests when the graph is not matched in a value fashion.

isAssignmentSafeEquality

public static boolean isAssignmentSafeEquality(Expr expr,
                                               boolean graphHasStringEquality,
                                               boolean graphHasNumercialValueEquality)

Parameters:

graphHasStringEquality - True if the graph triple matching equates xsd:string and plain literal

graphHasNumercialValueEquality - True if the graph triple matching equates numeric values

isStable

public static boolean isStable(Expr expr)

Some "functions" are non-deterministic (unstable) - calling them with the same arguments does not yields the same answer each time. Therefore how and when they are called matters. Functions: RAND, UUID, StrUUID, BNode NOW() is safe.

nodeToExpr

public static Expr nodeToExpr(Node n)

Go from a node to an expression.

rewriteTriple

public static Expr rewriteTriple(Triple t)