net.sf.saxon.expr
Class VennExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.BinaryExpression
          extended by net.sf.saxon.expr.VennExpression
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public class VennExpression
extends BinaryExpression

An expression representing a nodeset that is a union, difference, or intersection of two other NodeSets

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
VennExpression(Expression p1, int op, Expression p2)
          Constructor
 
Method Summary
 int computeCardinality()
          Determine the static cardinality of the expression
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 Expression copy()
          Copy an expression.
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value.
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the items returned by this expression
 int hashCode()
          Is this expression the same as another expression?
 SequenceIterator iterate(XPathContext c)
          Iterate over the value of the expression.
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression simplify(ExpressionVisitor visitor)
          Simplify the expression
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.BinaryExpression
equals, explain, getOperands, getOperator, iterateSubExpressions, promote, replaceSubExpression, setFlattened, toString
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

VennExpression

public VennExpression(Expression p1,
                      int op,
                      Expression p2)
Constructor

Parameters:
p1 - the left-hand operand
op - the operator (union, intersection, or difference)
p2 - the right-hand operand
Method Detail

getItemType

public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression

Specified by:
getItemType in class Expression
Parameters:
th - the type hierarchy cache
Returns:
the data type

computeCardinality

public final int computeCardinality()
Determine the static cardinality of the expression

Overrides:
computeCardinality in class BinaryExpression
Returns:
the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:
computeSpecialProperties in class BinaryExpression
Returns:
StaticProperty.NON_CREATIVE. This is overridden for some subclasses.

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
Simplify the expression

Overrides:
simplify in class BinaryExpression
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException
Type-check the expression

Overrides:
typeCheck in class BinaryExpression
Parameters:
visitor - an expression visitor
contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
                    throws XPathException
Perform optimisation of an expression and its subexpressions.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:
optimize in class BinaryExpression
Parameters:
visitor - an expression visitor
contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
Returns:
the original expression, rewritten if appropriate to optimize execution
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Specified by:
copy in class Expression
Returns:
the copy of the original expression

hashCode

public int hashCode()
Is this expression the same as another expression?

Overrides:
hashCode in class BinaryExpression

iterate

public SequenceIterator iterate(XPathContext c)
                         throws XPathException
Iterate over the value of the expression. The result will always be sorted in document order, with duplicates eliminated

Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in class Expression
Parameters:
c - The context for evaluation
Returns:
a SequenceIterator representing the union of the two operands
Throws:
XPathException - if any dynamic error occurs evaluating the expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
Get the effective boolean value. In the case of a union expression, this is reduced to an OR expression, for efficiency

Overrides:
effectiveBooleanValue in class Expression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression


Copyright (C) Michael H. Kay. All rights reserved.