Robotics Reference
In-Depth Information
fatal and often show themselves when a patient is already in hospital, for
example while recovering from heart surgery. The name MYCIN comes
from the fact that most of the drugs used in the treatment of bacter-
ial infections have names ending in “mycin”, for example, Neomycin,
Apramycin, Gentamycin and Streptomycin.
An attending doctor typically takes samples to determine the identity
of infectious organisms, but a positive identification of samples normally
takes 24 to 48 hours, by which time the patient might have died from
the infection, especially if suffering from meningitis. In many cases it
is therefore essential to begin treatment without knowing the results of
all the laboratory tests, and the diagnoses and treatments of these dis-
eases are sufficiently complex that a doctor will often seek the advice of a
bacteriological expert, which was MYCIN's role.
In a MYCIN dialogue the system first decided which organisms, if
any, were causing significant disease. Then it decided which drugs were
potentially of use in treating the organisms and finally it selected what it
considered to be the best drug or set of drugs. The strategy that controls
this task was coded for the knowledge-base as a simple rule that covered
the overall diagnostic process:
If
there is an organism which requires therapy
and
If
consideration has been given to possible other organisms which
require therapy
Then
compile a list of possible therapies and determine the best
therapy
Else
indicate that the patient does not require therapy
Because early treatment in this area of medicine is essential, doctors have
learned to work from partial information and therefore sometimes they
respond to MYCIN's questions with “UNKNOWN”, rather than wait
until they have all the information the system is requesting. This might
be necessary, for example, if MYCIN asks about a test for which the
results are not yet available, and when that happens MYCIN, just like a
human specialist, will be able to reason even though it has incomplete in-
formation. MYCIN might also ask the doctor for information of which
the doctor is uncertain. To accommodate uncertainty, all information
giventoMYCINmaybequalifiedbywhatiscalleda
certainty factor
,a
number between -1 and +1, that indicates the doctor's degree of confi-
dence in the answer to a question. Thus, if a doctor is only moderately
