org.basex.query.expr
Class Expr

java.lang.Object
  org.basex.query.ExprInfo
      org.basex.query.expr.Expr

Direct Known Subclasses:

Arr, FLWOR, FTContains, FTExpr, Group, Grp, Item, Ord, Order, Path, Preds, Satisfy, Simple, Single, TypeSwitch, Var, VarCall

public abstract class Expr
extends ExprInfo

Abstract expression.

Author:

Workgroup DBIS, University of Konstanz 2005-10, ISC License, Christian Gruen

Nested Class Summary

static class

Expr.Use Usage flags.

Constructor Summary

Expr()

Method Summary

Expr	addText(QueryContext ctx) Optionally adds a text node to an expression for potential index rewriting.
Item	atomic(QueryContext ctx) Evaluates the expression and returns the resulting item or a null reference.
Item	checkCtx(QueryContext ctx) Throws an exception if the context item is not set.
double	checkDbl(Expr e, QueryContext ctx) Checks if the specified expression yields a string.
long	checkItr(Expr e, QueryContext ctx) Checks if the specified expression is an integer.
abstract Expr	comp(QueryContext ctx) Optimizes and compiles the expression.
boolean	duplicates(QueryContext ctx) Returns true if the expression might yield duplicates and unsorted results.
boolean	e() Returns if this is an empty sequence.
Item	ebv(QueryContext ctx) Checks if the iterator can be dissolved into an effective boolean value.
boolean	i() Checks if this is an item.
boolean	indexAccessible(IndexContext ic) Checks if an index can be used for query evaluation.
Expr	indexEquivalent(IndexContext ic) Returns an equivalent expression which accesses an index structure.
Iter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
boolean	removable(Var v, QueryContext ctx) Checks if the specified variable is removable.
Expr	remove(Var v) Removes the specified variable in a sub expression.
Return	returned(QueryContext ctx) Indicates the return type of an expression.
boolean	sameAs(Expr cmp) Checks the current and specified expression for equality.
long	size(QueryContext ctx) Returns the sequence size or 1.
Item	test(QueryContext ctx) Performs a predicate test and returns the item if test was successful.
abstract boolean	uses(Expr.Use u, QueryContext ctx) Indicates if an expression uses the specified type.
boolean	v() Returns if this is a vacuous expression (empty sequence or error function).

Methods inherited from class org.basex.query.ExprInfo

color, info, name, plan, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

Expr

public Expr()

Method Detail

comp

public abstract Expr comp(QueryContext ctx)
                   throws QueryException

Optimizes and compiles the expression.

Parameters:

ctx - query context

Returns:

optimized Expression

Throws:

QueryException - query exception

iter

public Iter iter(QueryContext ctx)
          throws QueryException

Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, atomic(org.basex.query.QueryContext) must be implemented.

Parameters:

ctx - query context

Returns:

resulting item

Throws:

QueryException - query exception

atomic

public Item atomic(QueryContext ctx)
            throws QueryException

Evaluates the expression and returns the resulting item or a null reference. If this method is not overwritten, iter(org.basex.query.QueryContext) must be implemented.

Parameters:

ctx - query context

Returns:

iterator

Throws:

QueryException - query exception

ebv

public Item ebv(QueryContext ctx)
         throws QueryException

Checks if the iterator can be dissolved into an effective boolean value. If not, returns an error. If yes, returns the first value - which can be also be e.g. an integer, which is later evaluated as position predicate.

Parameters:

ctx - query context

Returns:

item

Throws:

QueryException - query exception

test

public Item test(QueryContext ctx)
          throws QueryException

Performs a predicate test and returns the item if test was successful.

Parameters:

ctx - query context

Returns:

item

Throws:

QueryException - query exception

i

public boolean i()

Checks if this is an item.

Returns:

result of check

e

public boolean e()

Returns if this is an empty sequence.

Returns:

result of check

v

public boolean v()

Returns if this is a vacuous expression (empty sequence or error function).

Returns:

result of check

size

public long size(QueryContext ctx)
          throws QueryException

Returns the sequence size or 1.

Parameters:

ctx - query context

Returns:

result of check

Throws:

QueryException - query exception

uses

public abstract boolean uses(Expr.Use u,
                             QueryContext ctx)

Indicates if an expression uses the specified type. Called by the compiler to perform certain optimizations. true is returned by default and thus assumed as "worst-case".

Parameters:

u - use type to be checked

ctx - query context

Returns:

result of check

removable

public boolean removable(Var v,
                         QueryContext ctx)

Checks if the specified variable is removable.

Parameters:

v - variable to be removed

ctx - query context

Returns:

result of check

remove

public Expr remove(Var v)

Removes the specified variable in a sub expression.

Parameters:

v - variable to be removed

Returns:

expression with removed variable

returned

public Return returned(QueryContext ctx)

Indicates the return type of an expression. Called by the compiler to check if expressions can be reformulated. null is returned by default.

Parameters:

ctx - query context

Returns:

result of check

duplicates

public boolean duplicates(QueryContext ctx)

Returns true if the expression might yield duplicates and unsorted results.

Parameters:

ctx - query context

Returns:

result of check

indexAccessible

public boolean indexAccessible(IndexContext ic)
                        throws QueryException

Checks if an index can be used for query evaluation.

Parameters:

ic - index context

Returns:

true if an index can be used

Throws:

QueryException - query exception

indexEquivalent

public Expr indexEquivalent(IndexContext ic)
                     throws QueryException

Returns an equivalent expression which accesses an index structure. Must be called if indexAccessible(org.basex.query.IndexContext) is implemented for an expression.

Parameters:

ic - index context

Returns:

Equivalent index-expression or null

Throws:

QueryException - query exception

sameAs

public boolean sameAs(Expr cmp)

Checks the current and specified expression for equality.

Parameters:

cmp - expression to be compared

Returns:

result of check

checkDbl

public final double checkDbl(Expr e,
                             QueryContext ctx)
                      throws QueryException

Checks if the specified expression yields a string. Returns a token representation or an exception.

Parameters:

e - expression to be checked

ctx - query context

Returns:

item

Throws:

QueryException - query exception

checkItr

public final long checkItr(Expr e,
                           QueryContext ctx)
                    throws QueryException

Checks if the specified expression is an integer. Returns a token representation or an exception.

Parameters:

e - expression to be checked

ctx - query context

Returns:

item

Throws:

QueryException - query exception

checkCtx

public final Item checkCtx(QueryContext ctx)
                    throws QueryException

Throws an exception if the context item is not set.

Parameters:

ctx - query context

Returns:

item if everything is ok

Throws:

QueryException - query exception

addText

public Expr addText(QueryContext ctx)
             throws QueryException

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

Parameters:

ctx - query context

Returns:

expression

Throws:

QueryException - query exception