About yahoo UI 2.6 data source


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)

   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.