net.sf.saxon.expr
Class PromotionOffer

java.lang.Object
  net.sf.saxon.expr.PromotionOffer

public class PromotionOffer
extends Object

PromotionOffer is an object used transiently during compilation of an expression. It contains information passed by a containing expression to its subexpressions, when looking for subexpressions that can be promoted to a higher level because they are not dependent on the context established by the containing expression. The object is also used to pass back return information when the promotion actually takes place.

Field Summary

boolean	accepted Flag that is set if the offer has been accepted, that is, if the expression has changed
int	action action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT, INLINE_VARIABLE_REFERENCES, UNORDERED, EXTRACT_GLOBAL_VARIABLES
Binding[]	bindingList In the case of RANGE_INDEPENDENT, "binding" identifies the range variables whose dependencies we are looking for.
Expression	containingExpression When a promotion offer is made, containingExpression identifies the level to which the promotion should occur.
static int	EXTRACT_GLOBAL_VARIABLES EXTRACT_GLOBAL_VARIABLES identifies subexpressions that are not constant, but have no dependencies other than on global variables or parameters (they must also be non-creative).
static int	FOCUS_INDEPENDENT FOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the focus.
static int	INLINE_VARIABLE_REFERENCES Inline variable references causes all references to a variable V to be replaced by the expression E.
boolean	mustEliminateDuplicates In the case of UNORDERED, "mustEliminateDuplicates" is a boolean that is set to true if the nodes can be delivered in any order so long as there are no duplicates (for example, as required by the count() function).
boolean	promoteDocumentDependent In the case of FOCUS_INDEPENDENT, "promoteDocumentDependent" is a boolean that, when set to true, indicates that it is safe to promote a subexpression that depends on the context document but not on other aspects of the focus.
boolean	promoteXSLTFunctions In the case of FOCUS_INDEPENDENT, "promoteXSLTFunctions" is a boolean that, when set to true, indicates that it is safe to promote XSLT functions such as current().
static int	RANGE_INDEPENDENT RANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a specified range variable.
static int	REPLACE_CURRENT REPLACE_CURRENT causes calls to the XSLT current() function to be replaced by reference to a variable.
static int	UNORDERED UNORDERED indicates that the containing expression does not require the results to be delivered in any particular order.
ExpressionVisitor	visitor The expression visitor in use

Constructor Summary

PromotionOffer(Optimizer optimizer)
Create a PromotionOffer for use with a particular Optimizer

Method Summary

Expression	accept(Expression child) Method to test whether a subexpression qualifies for promotion, and if so, to accept the promotion.
Optimizer	getOptimizer() Get the optimizer in use

Methods inherited from class java.lang.Object

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

Field Detail

FOCUS_INDEPENDENT

public static final int FOCUS_INDEPENDENT

FOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the focus. This is typically used to extract subexpressions from a filter predicate. The offer is optional - each subexpression can decide whether it's worth the trouble of promoting itself. The offer is normally passed on to subexpressions, except subexpressions that are evaluated with a different focus

See Also:

Constant Field Values

RANGE_INDEPENDENT

public static final int RANGE_INDEPENDENT

RANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a specified range variable. This is typically used to extract subexpressions from the action of a for expression or the condition of a some/every quantified expression. The offer is optional - each subexpression can decide whether it's worth the trouble of promoting itself. The offer is normally passed on to subexpressions, except subexpressions that are evaluated with a different focus or a different range variable, because these may have other dependencies that prevent their promotion.

See Also:

Constant Field Values

INLINE_VARIABLE_REFERENCES

public static final int INLINE_VARIABLE_REFERENCES

Inline variable references causes all references to a variable V to be replaced by the expression E. The variable is supplied in the "binding" property; the replacement expression in the containingExpression property. A special case is where the replacement expression is a ContextItemExpression; in this case the offer is not passed on to subexpressions where the context is different.

See Also:

Constant Field Values

UNORDERED

public static final int UNORDERED

UNORDERED indicates that the containing expression does not require the results to be delivered in any particular order. The boolean mustEliminateDuplicates is set if duplicate items in the result are not allowed.

See Also:

Constant Field Values

REPLACE_CURRENT

public static final int REPLACE_CURRENT

REPLACE_CURRENT causes calls to the XSLT current() function to be replaced by reference to a variable. The variable binding is the single member of the array bindingList

See Also:

Constant Field Values

EXTRACT_GLOBAL_VARIABLES

public static final int EXTRACT_GLOBAL_VARIABLES

EXTRACT_GLOBAL_VARIABLES identifies subexpressions that are not constant, but have no dependencies other than on global variables or parameters (they must also be non-creative). Such expressions can be extracted from a function or template and converted into global variables. This optimization is done in Saxon-SA only.

See Also:

Constant Field Values

visitor

public ExpressionVisitor visitor

The expression visitor in use

action

public int action

action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT, INLINE_VARIABLE_REFERENCES, UNORDERED, EXTRACT_GLOBAL_VARIABLES

promoteDocumentDependent

public boolean promoteDocumentDependent

In the case of FOCUS_INDEPENDENT, "promoteDocumentDependent" is a boolean that, when set to true, indicates that it is safe to promote a subexpression that depends on the context document but not on other aspects of the focus. This is the case, for example, in a filter expression when it is known that all the nodes selected by the expression will be in the same document - as happens when the filter is applied to a path expression. This allows subexpressions such as key() to be promoted

promoteXSLTFunctions

public boolean promoteXSLTFunctions

In the case of FOCUS_INDEPENDENT, "promoteXSLTFunctions" is a boolean that, when set to true, indicates that it is safe to promote XSLT functions such as current(). This flag is set when rewriting XPath expressions and is unset when rewriting XSLT templates.

mustEliminateDuplicates

public boolean mustEliminateDuplicates

In the case of UNORDERED, "mustEliminateDuplicates" is a boolean that is set to true if the nodes can be delivered in any order so long as there are no duplicates (for example, as required by the count() function). If this boolean is false, the nodes can be delivered in any order and duplicates are allowed (for example, as required by the boolean() function).

bindingList

public Binding[] bindingList

In the case of RANGE_INDEPENDENT, "binding" identifies the range variables whose dependencies we are looking for. For INLINE_VARIABLE_REFERENCES it is a single Binding that we are aiming to inline

containingExpression

public Expression containingExpression

When a promotion offer is made, containingExpression identifies the level to which the promotion should occur. When a subexpression is promoted, an expression of the form let $VAR := SUB return ORIG is created, and this replaces the original containingExpression within the PromotionOffer.

accepted

public boolean accepted

Flag that is set if the offer has been accepted, that is, if the expression has changed

Constructor Detail

PromotionOffer

public PromotionOffer(Optimizer optimizer)

Create a PromotionOffer for use with a particular Optimizer

Parameters:

optimizer - the optimizer

Method Detail

getOptimizer

public Optimizer getOptimizer()

Get the optimizer in use

Returns:

the optimizer

accept

public Expression accept(Expression child)
                  throws XPathException

Method to test whether a subexpression qualifies for promotion, and if so, to accept the promotion.

Parameters:

child - the subexpression in question

Returns:

if promotion was done, returns the expression that should be used in place of the child expression. If no promotion was done, returns null. If promotion is determined not to be necessary for this subtree, returns the supplied child expression unchanged

Throws:

XPathException