org.basex.query.path

Class AxisPath

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.expr.ParseExpr

org.basex.query.path.Path

org.basex.query.path.AxisPath

public class AxisPath
extends Path

Axis path expression.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Expr.Use

Field Summary

Fields inherited from class org.basex.query.path.Path

root, steps

Fields inherited from class org.basex.query.expr.ParseExpr

input, size, type

Method Summary

Methods

Modifier and Type	Method and Description
Expr	addText(QueryContext ctx) Optionally adds a text node to an expression for potential index rewriting.
protected Expr	compPath(QueryContext ctx) Compiles the location path.
Path	copy() Returns a copy of the path expression.
int	count(Var v) Counts how often the specified variable is used by an expression.
AxisPath	invertPath(Expr r, AxisStep curr) Inverts a location path.
Iter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
boolean	iterable() Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted.
java.util.ArrayList<PathNode>	nodes(QueryContext ctx) Returns the path nodes that will result from this path.
boolean	removable(Var v) Checks if the specified variable is replaceable by a context item.
Expr	remove(Var v) Substitutes all VarRef expressions for the given variable by a Context reference.
boolean	sameAs(Expr cmp) Compares the current and specified expression for equality.
AxisStep	step(int i) Returns the specified axis step.

Methods inherited from class org.basex.query.path.Path

addPreds, comp, get, plan, toString, uses

Methods inherited from class org.basex.query.expr.ParseExpr

checkBln, checkColl, checkCreate, checkCtx, checkDbl, checkDBNode, checkEStr, checkEStr, checkIO, checkItem, checkItr, checkItr, checkMap, checkNode, checkNoEmpty, checkStr, checkType, checkUp, checkUp, checkWrite, compBln, ebv, item, optPre, preEval, size, test, type, value

Methods inherited from class org.basex.query.expr.Expr

compEbv, hasFreeVars, indexAccessible, indexEquivalent, isEmpty, isFunction, isItem, isVacuous, isValue, markTailCalls

Methods inherited from class org.basex.data.ExprInfo

description, info

Methods inherited from class java.lang.Object

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

Method Detail

compPath

protected final Expr compPath(QueryContext ctx)
                       throws QueryException

Description copied from class: Path

Compiles the location path.

Specified by:

compPath in class Path

Parameters:

ctx - query context

Returns:

optimized expression

Throws:

QueryException - query exception

iter

public Iter iter(QueryContext ctx)
          throws QueryException

Description copied from class: Expr

Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, Expr.item(org.basex.query.QueryContext, org.basex.util.InputInfo) must be implemented by an expression, as it may be called by this method.

Overrides:

iter in class ParseExpr

Parameters:

ctx - query context

Returns:

resulting item

Throws:

QueryException - query exception

invertPath

public final AxisPath invertPath(Expr r,
                  AxisStep curr)

Inverts a location path.

Parameters:

r - new root node

curr - current location step

Returns:

inverted path

addText

public final Expr addText(QueryContext ctx)

Description copied from class: Expr

Optionally adds a text node to an expression for potential index rewriting.

Overrides:

addText in class Expr

Parameters:

ctx - query context

Returns:

expression

step

public final AxisStep step(int i)

Returns the specified axis step.

Parameters:

i - index

Returns:

step

copy

public final Path copy()

Returns a copy of the path expression.

Returns:

copy

nodes

public java.util.ArrayList<PathNode> nodes(QueryContext ctx)

Returns the path nodes that will result from this path.

Parameters:

ctx - query context

Returns:

path nodes, or null if nodes cannot be evaluated

count

public final int count(Var v)

Description copied from class: Expr

Counts how often the specified variable is used by an expression. This method is called by:

• GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates and remove statically bound or unused clauses
• GFLWOR.compHoist(org.basex.query.QueryContext) to hoist independent variables

Overrides:

count in class Path

Parameters:

v - variable to be checked

Returns:

number of occurrences

removable

public final boolean removable(Var v)

Description copied from class: Expr

Checks if the specified variable is replaceable by a context item. The following tests might return false:

• Preds.removable(org.basex.query.util.Var), if one of the variables is used within a predicate.
• MixedPath.removable(org.basex.query.util.Var), if the variable occurs within the path.
• Group.removable(org.basex.query.util.Var), as the group by expression depends on variable references.

This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses into predicates.

Overrides:

removable in class Path

Parameters:

v - variable to be replaced

Returns:

result of check

remove

public final Expr remove(Var v)

Description copied from class: Expr

Substitutes all VarRef expressions for the given variable by a Context reference. This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates.

Overrides:

remove in class Path

Parameters:

v - variable to be replaced

Returns:

new expression

iterable

public final boolean iterable()

Description copied from class: Expr

Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted. This method is called e.g. by AxisPath.

Overrides:

iterable in class Expr

Returns:

result of check

sameAs

public final boolean sameAs(Expr cmp)

Description copied from class: Expr

Compares the current and specified expression for equality.

Overrides:

sameAs in class Expr

Parameters:

cmp - expression to be compared

Returns:

result of check