net.sf.saxon.expr
Class Atomizer

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

public final class Atomizer
extends UnaryExpression

An Atomizer is an expression corresponding essentially to the fn:data() function: it maps a sequence by replacing nodes with their typed values

See Also:
Serialized Form

Nested Class Summary
static class Atomizer.AtomizingFunction
          Implement the mapping function.
 
Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
Atomizer(Expression sequence, Configuration config)
          Constructor
 
Method Summary
 PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
          Add a representation of this expression to a PathMap.
 int computeCardinality()
          Determine the static cardinality of the expression
 int computeSpecialProperties()
          Determine the special properties of this expression
 Expression copy()
          Copy an expression.
 String displayExpressionName()
          Diagnostic print of expression structure.
 Item evaluateItem(XPathContext context)
          Evaluate as an Item.
static ItemType getAtomizedItemType(Expression operand, boolean alwaysUntyped, TypeHierarchy th)
          Compute the type that will result from atomizing the result of a given expression
static SequenceIterator getAtomizingIterator(SequenceIterator base)
          Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the items returned by the expression, if possible
 SequenceIterator iterate(XPathContext context)
          Iterate over the sequence of values
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.UnaryExpression
equals, explain, getBaseExpression, hashCode, iterateSubExpressions, promote, replaceSubExpression, toString
 
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, 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, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Atomizer

public Atomizer(Expression sequence,
                Configuration config)
Constructor

Parameters:
sequence - the sequence to be atomized
config - the Configuration. Used only for optimization, may be null. Atomization is faster if it is known in advance that all nodes will be untyped.
Method Detail

simplify

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

Overrides:
simplify in class UnaryExpression
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 UnaryExpression
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 UnaryExpression
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)

computeSpecialProperties

public int computeSpecialProperties()
Determine the special properties of this expression

Overrides:
computeSpecialProperties in class UnaryExpression
Returns:
StaticProperty.NON_CREATIVE.

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Iterate over the sequence of values

Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in class Expression
Parameters:
context - supplies the context for evaluation
Returns:
a SequenceIterator that can be used to iterate over the result of the expression
Throws:
XPathException - if any dynamic error occurs evaluating the expression

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate as an Item. This should only be called if the Atomizer has cardinality zero-or-one, which will only be the case if the underlying expression has cardinality zero-or-one.

Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in class Expression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
Throws:
XPathException - if any dynamic error occurs evaluating the expression

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible

Overrides:
getItemType in class UnaryExpression
Parameters:
th - the type hierarchy cache
Returns:
a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER. For this class, the result is always an atomic type, but it might be more specific.

getAtomizedItemType

public static ItemType getAtomizedItemType(Expression operand,
                                           boolean alwaysUntyped,
                                           TypeHierarchy th)
Compute the type that will result from atomizing the result of a given expression

Parameters:
operand - the given expression
alwaysUntyped - true if it is known that nodes will always be untyped
th - the type hierarchy cache
Returns:
the item type of the result of evaluating the operand expression, after atomization

computeCardinality

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

Overrides:
computeCardinality in class UnaryExpression
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

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Overrides:
addToPathMap in class Expression
Parameters:
pathMap - the PathMap to which the expression should be added
pathMapNodeSet - the PathMapNodeSet to which the paths embodied in this expression should be added
Returns:
the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

getAtomizingIterator

public static SequenceIterator getAtomizingIterator(SequenceIterator base)
Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator

Parameters:
base - the supplied iterator, the input to atomization
Returns:
an iterator that returns atomic values, the result of the atomization

displayExpressionName

public String displayExpressionName()
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.



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