What you describe is essentially a general practitioner. If you look at what they do (and how their training is organised), they essentially follow decision tre

What you describe is essentially a general practitioner. If you look at what they do (and how their training is organised), they essentially follow decision trees to either a clear diagnosis or "refer to specialist". The difficulty for using computers for this tasks is that several of the things going into the tree are based on observations of the patients behaviour, look, speech etc., which is difficult to categorise for a machine.