PHP and XML

Dear friends, I have never done this before but i have to do the below sometime soon. I have an xml file that needs to be edited using php via the web.We want to edit its attributes and then save the updated xml file to a database field. Is this possible please put me on the right track. I am so new to this i am looking on the internet to find something useful. Please help if you know whwere i can get soemthing or if ne of u have done similar xml file editing using php. Thanks, Harpreet Kaur