Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/MemberRef.java
return member[0].isList( );
			case PROPERTY_MEMBER_MEMBER :
			case PROPERTY_MEMBER_LISTn_MEMBER :
			case PROPERTY_LISTn_MEMBER_LISTn_MEMBER :
			case PROPERTY_LISTn_MEMBER_MEMBER :
				return member[1].isList( );
			default :
				return false;
		}
	}
	/**
	 * Returns the structure at the given position in structure list.
	 * 
	 * @param list
	 *            structure list
	 * @param level
	 *            the structure position in first index or second index
	 * @return structure if the position is in list range, otherwise, return
	 *         null.
	 */
	Structure getStructure( List list, int level )
	{
		assert level == 0 || level == 1;
		if ( list == null )
			return null;
		if ( index[level] < 0 || index[level] >= list.size( ) )
			return null;
		return (Structure) list.get( index[level] );
	}
}