public abstract class PeriodRelation extends Relation
{
	public abstract AllenPeriodRelation toAllenPeriodRelation();
	public abstract SymbolicPeriodRelation toSymbolicPeriodRelation()
		throws TranslationException;
	public abstract PointPeriodRelation toPointPeriodRelation() 
		throws TranslationException;
	public abstract PointPeriodRelation[] toPointPeriodRelations();
}