The term Medical Knowledge is a superimposed concept for the complicated relationships that exist between symptoms and symptoms, symptoms and diagnoses, diagnoses and diagnoses and more complex relationships of combinations of symptoms and diagnoses to a symptom or diagnosis.

In the field of medicine, Symptoms are defined as (abnormal) traits noted by the patient and by the physician and Signs as (abnormal) traits noted by the medical practitioner. Since the symptoms are typically reported by the patient and confirmed by the medical practitioner, symptoms are included by signs as a subclass. Every symptom and sign has some biological basis, by which we mean that there exist physiological and/or pathological functions and processes which cause the given symptom or sign. In addition to symptoms and signs, Findings are considered to be results got by searching or making an effort (e.g., the effort of an examination). Diagnosis is then a medical term which describes exactly a disease. Based on these definitions, the certain information about relationships between symptoms, clinical findings, laboratory data and diagnostic hypotheses that a physician may find in books, journals, monographs, but also in practical experience are formalizations of what is called medical knowledge.

There is no unique, coherent, and commonly accepted model of medical terminology and medical knowledge —one may consider the various distinct approaches—, and hence, it’s necessary to introduce a pragmatic and simple but specialized model to accomplish the objectives of building medical knowledge base for any medical decision-support system. As a result, we will use one of the most comprehensive models proposed to describe medical knowledge by Deutsch et al in 1994. Deutsch and his colleagues presented a multi-layered structure to describe medical knowledge as shown in figure.

By analyzing this figure we see:

1. The left hand side (‘Tests’) and the right hand side (‘Therapies’) of this picture are actions which may be regarded as being orthogonal to the
2. Middle part. This part is made up by a hierarchy of abstractions:

   The lowest level, the ‘Observations’ layer, contains results of the ‘Tests’ layer. Such a test result is usually quantitative (numeric value) or qualitative (symbolic or Boolean type).

   In the middle of the hierarchy the first level of abstraction, the ‘Pathophysiological states’ layer, is inserted. Such states are usually judgments of statements about the patient’s state.

3. The topmost layer constitutes the actual result of the diagnostic procedure: The disease layer. Within this layer the diseases may be arranged in levels of abstractions, too. These diseases lead to the ‘Therapies’ layer which contains the actual therapeutic procedures.

 

This structure in one of the most advantageous ones used to describe medical knowledge.