lux.xpath

Class PathExpression

java.lang.Object

lux.xpath.AbstractExpression

lux.xpath.PathExpression

All Implemented Interfaces:

Visitable

public class PathExpression
extends AbstractExpression

A path expression represents two expressions joined with a "/"

Author:

sokolov

Nested Class Summary

Nested classes/interfaces inherited from class lux.xpath.AbstractExpression

AbstractExpression.Type

Field Summary

Fields inherited from class lux.xpath.AbstractExpression

subs, sup

Constructor Summary

Constructors

Constructor and Description
PathExpression(AbstractExpression lhs, AbstractExpression rhs)

Method Summary

Methods

Modifier and Type	Method and Description
AbstractExpression	accept(ExpressionVisitor visitor)
boolean	geq(AbstractExpression other)
VariableContext	getBindingContext() If this expression depends "directly" on a variable, return that variable's binding context: a for or let clause, or a global variable definition.
AbstractExpression	getHead()
AbstractExpression	getLastContextStep() This method is called by the optimizer in order to determine an element or attribute QName (or wildcard) against which some expression is being compared, in order to generate an appropriate text query.
AbstractExpression	getLHS()
int	getPrecedence()
AbstractExpression	getRHS()
AbstractExpression	getRoot() Whenever we see a new absolute context (/, collection(), search()), its dependent expressions are a possible target for optimization.
AbstractExpression	getTail()
boolean	isRestrictive() An expression is restrictive when any empty sub implies the expression is empty.
boolean	matchDown(AbstractExpression fieldExpr, AbstractExpression fromExpr) Traverse downwards, comparing with fromExpr for equivalence until one bottoms out, ignoring fromExpr (since it has already been checked).
void	toString(StringBuilder buf) Each subclass must implement the toString(StringBuilder) method by appending itself as a syntatically valid XPath/XQuery expression in the given buffer.

Methods inherited from class lux.xpath.AbstractExpression

acceptSubs, appendSub, deepEquals, equivalent, getSubs, getSuper, getType, isAbsolute, isDocumentOrdered, propEquals, propGreaterEqual, replaceRoot, setSubs, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

PathExpression

public PathExpression(AbstractExpression lhs,
              AbstractExpression rhs)

Method Detail

getRHS

public final AbstractExpression getRHS()

getLHS

public final AbstractExpression getLHS()

getPrecedence

public int getPrecedence()

Specified by:

getPrecedence in class AbstractExpression

Returns:

18

toString

public void toString(StringBuilder buf)

Description copied from class: AbstractExpression

Each subclass must implement the toString(StringBuilder) method by appending itself as a syntatically valid XPath/XQuery expression in the given buffer.

Specified by:

toString in class AbstractExpression

Parameters:

buf - the buffer to append to

getRoot

public AbstractExpression getRoot()

Whenever we see a new absolute context (/, collection(), search()), its dependent expressions are a possible target for optimization.

Overrides:

getRoot in class AbstractExpression

Returns:

the root of this path, or null if it is not an absolute path.

accept

public AbstractExpression accept(ExpressionVisitor visitor)

getHead

public AbstractExpression getHead()

Overrides:

getHead in class AbstractExpression

Returns:

the leftmost path sub-expression

getTail

public AbstractExpression getTail()

Overrides:

getTail in class AbstractExpression

Returns:

the expression remaining after removing the left-most sub-expression (the CDR).

getLastContextStep

public AbstractExpression getLastContextStep()

Description copied from class: AbstractExpression

This method is called by the optimizer in order to determine an element or attribute QName (or wildcard) against which some expression is being compared, in order to generate an appropriate text query.

Overrides:

getLastContextStep in class AbstractExpression

Returns:

the rightmost step of this path expression

getBindingContext

public VariableContext getBindingContext()

Description copied from class: AbstractExpression

If this expression depends "directly" on a variable, return that variable's binding context: a for or let clause, or a global variable definition. This recurses through variables, so if there are aliases it retrieves the ultimate context. We need to define directly dependent precisely; what it's used for is to determine with an order by expression is dependent on a for-variable, and ultimately whether an order by optimization can be applied.

Overrides:

getBindingContext in class AbstractExpression

Returns:

the context in which a variable in the LHS of the path is bound, if any

isRestrictive

public boolean isRestrictive()

Description copied from class: AbstractExpression

An expression is restrictive when any empty sub implies the expression is empty. In other words, restrictive expressions only return results when all of their subs are non-empty. Eg: and, intersect, predicate, path step.

Overrides:

isRestrictive in class AbstractExpression

Returns:

whether this expression is restrictive

geq

public boolean geq(AbstractExpression other)

Overrides:

geq in class AbstractExpression

Parameters:

other - another expression

Returns:

whether the two expressions are s.t. this expr is non-empty whenever (for whichever contexts) the other one is.

matchDown

public boolean matchDown(AbstractExpression fieldExpr,
                AbstractExpression fromExpr)

Description copied from class: AbstractExpression

Traverse downwards, comparing with fromExpr for equivalence until one bottoms out, ignoring fromExpr (since it has already been checked).

Overrides:

matchDown in class AbstractExpression

Returns:

whether fieldExpr >= queryExpr