de.fuberlin.wiwiss.d2rq.algebra

Class MutableRelation

java.lang.Object

de.fuberlin.wiwiss.d2rq.algebra.MutableRelation

All Implemented Interfaces:

RelationalOperators

public class MutableRelation
extends Object
implements RelationalOperators

Wraps a relation and allows it to be modified by relational operators. Normally, applying an operator to a relation results in a new object. This is impractical in some places. The MutableRelation solves this problem.

Author:

Richard Cyganiak (richard@cyganiak.de)

Field Summary

Fields inherited from interface de.fuberlin.wiwiss.d2rq.algebra.RelationalOperators

DUMMY

Constructor Summary

Constructors

Constructor and Description
MutableRelation(Relation initialState)

Method Summary

Methods

Modifier and Type	Method and Description
Relation	empty()
Relation	immutableSnapshot()
Relation	limit(int limit)
Relation	orderBy(List<OrderSpec> orderSpecs)
Relation	project(Set<? extends ProjectionSpec> projectionSpecs) Applies the projection operator to this relation.
Relation	renameColumns(ColumnRenamer renamer) Applies the rename operator to this relation.
Relation	select(Expression condition) Applies the selection operator to this relation.
Relation	swapLimits()

Methods inherited from class java.lang.Object

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

Constructor Detail

MutableRelation

public MutableRelation(Relation initialState)

Method Detail

immutableSnapshot

public Relation immutableSnapshot()

renameColumns

public Relation renameColumns(ColumnRenamer renamer)

Description copied from interface: RelationalOperators

Applies the rename operator to this relation.

Renames of attributes that don't exist in the relation are ignored.

Specified by:

renameColumns in interface RelationalOperators

Parameters:

renamer - A map from original to replacement names

Returns:

A relation in which all occurrences of the old names have been replaced with the new ones

empty

public Relation empty()

select

public Relation select(Expression condition)

Description copied from interface: RelationalOperators

Applies the selection operator to this relation. The new relation will contain only the tuples for which the expression evaluates to true.

Selection on attributes that don't exist in the relation are considered to be always false and will cause an empty relation.

Specified by:

select in interface RelationalOperators

Parameters:

condition - A boolean expression

Returns:

A relation whose tuples satisfy the condition

orderBy

public Relation orderBy(List<OrderSpec> orderSpecs)

swapLimits

public Relation swapLimits()

project

public Relation project(Set<? extends ProjectionSpec> projectionSpecs)

Description copied from interface: RelationalOperators

Applies the projection operator to this relation.

The new relation will contain only the attributes given as the argument.

Specified by:

project in interface RelationalOperators

Parameters:

projectionSpecs - A set of ProjectionSpec instances

Returns:

A relation having the specified attributes

limit

public Relation limit(int limit)