org.jrdf.query.relation.constants
Class RelationDUM

java.lang.Object
  org.jrdf.query.relation.constants.RelationDUM

All Implemented Interfaces:

Serializable, Relation

public final class RelationDUM
extends Object
implements Relation, Serializable

Dum is a relation with no tuples and is the base relation for FALSE.

Version:

$Revision: 1822 $

Author:

Andrew Newman

See Also:

Serialized Form

Field Summary

static Relation

RELATION_DUM The singleton version of RelationDUM.

Method Summary

Set<Attribute>	getHeading() This Relation has no attributes.
SortedSet<Attribute>	getSortedHeading()
SortedSet<Tuple>	getSortedTuples()
Set<Tuple>	getTuples() Returns an empty set of tuples.

Methods inherited from class java.lang.Object

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

Field Detail

RELATION_DUM

public static final Relation RELATION_DUM

The singleton version of RelationDUM.

Method Detail

getHeading

public Set<Attribute> getHeading()

This Relation has no attributes.

Specified by:

getHeading in interface Relation

Returns:

an empty set.

getTuples

public Set<Tuple> getTuples()

Returns an empty set of tuples.

Specified by:

getTuples in interface Relation

Returns:

an empty set of tuples.

getSortedHeading

public SortedSet<Attribute> getSortedHeading()

Specified by:

getSortedHeading in interface Relation

getSortedTuples

public SortedSet<Tuple> getSortedTuples()

Specified by:

getSortedTuples in interface Relation