Information Technology Reference
In-Depth Information
22
Towards an Interpretation
of the Medical Expert System CADIAG 2
David Picado Muiño, Agata Ciabattoni, and Thomas Vetterlein
22.1
Introduction
CADIAG2 (Computer Assisted DIAGnosis) is a well known rule-based expert sys-
tem that aims at providing support in diagnostic decision making in the field of
internal medicine. Its design and construction was initiated in the early 80's at the
University of Vienna Medical School (now Medical University of Vienna) by Klaus-
Peter Adlassnig -see [20] for a historical perspective on the origins and motivations
of the system-.
CADIAG2 consists basically of two pieces: a knowledge base and an inference
engine. CADIAG2's knowledge base is given by a set of
IF-THEN
rules, also known
as production rules in the literature, intended to represent relationships between
distinct medical entities: symptoms, findings, signs and test results on the one hand
(to which we will commonly refer as
symptoms
) and diseases and therapies on the
other one (to which we will commonly refer as
diagnoses
). The rules in CADIAG2
are defined along with a certain
degree of confirmation
which is intended to express
the degree to which the antecedent confirms the consequent. For example,
IF suspicion of liver metastases by palpation
THEN pancreatic cancer
with degree of confirmation
0
.
3
The inference engine in CADIAG2 takes as its input (possibly) imprecise medical
information about the patient, normally in the form of a set of symptoms present to
some degree in the patient, and yields as its output a set of possible diagnoses, each
along with a value intended to represent some degree of certainty about its presence
in the patient. The inference rules in the knowledge base of the system are brought
into play along the inference process, which is mostly based on methodology and
techniques derived from fuzzy set theory, in the sense of [23] and [24].
The main aim of the present paper responds to an attempt to interpret the infer-
ence process in CADIAG2, and ultimately the output of the system, on the grounds
