Thanks Frederico and Mary for your reply. I will update here once I got a chance in the "office hour".
@Frederico I agree with you that the role should consult with lead link when making some decision regarding to technology to use. So this is what policy is about. I think we are going to officiate it as our circle policy, as currently it's just feels right to do so.
@Mary, my understanding to technology or architecture for a web service in our site is like paint for a room in a house. So when the room is domain of a role, one of the task is to choose what color to apply there. Do you think I understand it correctly here?