How to conditionally show sub-forms depending on a data connection file?.

Hi, let say I have a form that shows a car specification and consists of N parts (sub-forms):

part I

part II

part III

...

part N

Those parts are sub-forms, and given a specific xml data connection file, I need to show the parts if and only iff certain elements of that xml exist or not. Let say, part II is called: "airbag", but if the car doesn't come with airbag (in the xml the airbag section doesn't exist) then the subform should not appear.

How can I do this?.

Thanks!.