Doctors are similar. They listen to your description of your symptoms and then ask searching questions to determine the probable cause of your illness. The difficulty is that different illnesses have this irritating habit of presenting very similar symptoms and it is the Doctor's skill and experience that enables him to determine the underlying cause of your discomfort.
Yesterday, the swine flu hot line was launched. The hot line is manned by people who are not Doctors. They have a series of questions to ask to determine whether you have swine flu. It is an automatic process that cannot possibly replace a Doctor. There is always the possibility that someone with a different illness could be misdiagnosed. It was predicted here and it has already occurred, see here