[galaxy-dev] How to get raw file name of the uploaded dataset

Dear all, May I ask how to get the raw file name of the uploaded dataset? The value of $input assigned from <param name="input" type="data" format="xml"> is a file name like "dist-path/database/files/000/dataset_12.dat". However, I really need to get the raw file name like "abc.xml" which seems to be stored as attribute "name" of the uploaded dataset. How can I get the raw file name? Please help me. Thank you very much. Yingwei HU