net.sf.saxon.expr
Class VennExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.BinaryExpression
          net.sf.saxon.expr.VennExpression

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

Direct Known Subclasses:

SingletonIntersectExpression

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.BinaryExpression

operand0, operand1, operator

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_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.
boolean	equals(Object other) Is this expression the same as another expression?
void	gatherComponents(int operator, Set set) Gather the component operands of a union or intersect expression
String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by this expression
int	hashCode() Get a hashCode for comparing two expressions.
SequenceIterator	iterate(XPathContext c) Iterate over the value of the expression.
Expression	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	simplify(ExpressionVisitor visitor) Simplify the expression
Expression	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expression

Methods inherited from class net.sf.saxon.expr.BinaryExpression

displayOperator, explain, explainExtraAttributes, getArguments, getOperands, getOperator, isAssociative, isCommutative, isInverse, iterateSubExpressions, promote, replaceSubExpression, setFlattened, toString

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

clone, finalize, 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

getExpressionName

public String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

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.

gatherComponents

public void gatherComponents(int operator,
                             Set set)

Gather the component operands of a union or intersect expression

Parameters:

operator - union or intersect

set - the set into which the components are to be gathered. If the operator is union, this follows the tree gathering all operands of union expressions. Ditto, mutatis mutandis, for intersect expressions.

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,
                            ExpressionVisitor.ContextItemType 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,
                           ExpressionVisitor.ContextItemType 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

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class BinaryExpression

hashCode

public int hashCode()

Description copied from class: BinaryExpression

Get a hashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

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

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