At his stage, the mapping has two source components (Books and Library) and one target component (Library). Now we have two components with the same name - Library. To avoid confusion, we need to change the settings in the Component Settings dialog box. Double-click the header of each component. Then verify and change the name and the input/output files of each component as shown below.
As shown above, the first source component reads data from Books.xml. The second source component reads data from Library.xml. Finally, the target component outputs data to a file called MergedLibrary.xml.