What is a diagnosis?

The Bertalanffy Center of System Science organized a workshop asking about “Health and Big Data”. My question was “What are Symptoms? What is a diagnosis and what is judgement of pain?”. The presentation was well received and further question lead actually to the question “What is health?”.
One thing could be concluded: We can´t assume, that a practical work of a medical practitioner can be replaced by data from the past. This leads again to the “here and now” as initial principle of reality.