about yahoo UI 2.6 data source

hi,
    I am using yahoo UI autocomplete in my rails application.
     I want to use XML data format.
     I have a tag_list field in view file.
     this is my code in controller
      def filter_tag
       @tags= Tags.find(:all)
       end

       I can not understand how can I format the resultant data(@tags)
in xml format for response.
       please give me some example source. I have googled a lot but not
find any
example for that.
       I am very new with the yahoo iu. I have configure the view
according to the documentation of yahoo ui autocomplete but trouble with
code in the method in the controller.
       Please guide me.
       Amin