Irule with Datagroup External file is not working. Please help

I do not have a version 10.x unit I can test with at the moment, but the wiki page for the class command outlines something almost exactly like what you are looking for if I understand your requirements right. They just go about doing it in a little different way:

http://devcentral.f5.com/wiki/default.aspx/iRules/class.html

The recommend setting up your data group like this:

/config/app_class.dat:

"/trxdef/" := "trx_pool",

"/aaa/" := "aaa_pool",

"/abscon/" := "abs_pool",

class app_class {

type string

filename app_class.dat

}

 
   when HTTP_REQUEST {
      set app_pool [class match –value [HTTP::uri] starts_with app_class]
      if {$app_pool ne ""} {
         pool $app_pool
      } else {
         pool default_pool
      }
   }
}