Bug 183918 get relative file path of linkage library
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/library/DesignLoadLibraryTest.java
designHandle.getCommandStack( ).undo( );
		assertEquals(
				"LibA.dataSet1", table1.getStringProperty( TableHandle.DATA_SET_PROP ) ); 
		assertNotNull( table1.getDataSet( ) );
		
		designHandle.getCommandStack( ).redo( );
		assertEquals(
				"dataSet2", table1.getStringProperty( TableHandle.DATA_SET_PROP ) ); 
		assertEquals( dataSet2, table1.getDataSet( ) );
		
		designHandle.getCommandStack( ).redo( );
		assertEquals( "LibA.dataSet1", table1 
				.getStringProperty( TableHandle.DATA_SET_PROP ) );
		
		
		TableHandle table2 = (TableHandle) designHandle.findElement( "table2" ); 
		assertNotNull( table2.getDataSet( ) );
		assertEquals( "dataSet2", table2.getDataSet( ).getName( ) ); 
		table2.getDataSet( ).drop( );
		assertNull( table2.getDataSet( ) );
		assertEquals(
				"dataSet2", table2.getStringProperty( TableHandle.DATA_SET_PROP ) ); 
		TableHandle table4 = (TableHandle) designHandle.findElement( "table4" ); 
		assertNotNull( table4.getDataSet( ) );
		assertEquals( "dataSet4", table4.getDataSet( ).getName( ) ); 		
	}
	/**
	 * Tests the property search rules for the design element extending one lib
	 * element.
	 *