An Expert System on Detection, Evaluation and Treatment of Hypertension - Artificial Intelligence and Symbolic Computation - page 257

Table 4. Table 2, once corrected

Category SBP mmHg DBP mmHg

Normal < 120 and < 80

120-139 and < 90

Prehypertension or

< 140 and 80-89

140-159 and < 100

Hypertension, Stage 1 or

< 160 and 90-99

160-179 and < 110

Hypertension, Stage 2a or

< 180 and 100-109

Hypertension, Stage 2b ≥ 180 or ≥ 110

Table 5. Classification of CVD risk when hypertension is present

CVD Risk Factors
and other CVD facts St. 1 Hyp. St. 2a Hyp. St. 2b Hyp.

0CVDRF Low Medium High

1or2CVDRF Medium Medium Very high

≥ 3CVDRF ∨ TOD ∨ DM High High Very high

ACA Very high Very high Very high

the last row of those first two columns has no sense, as without hypertension
there can be no ACA associated to hypertension.

5 Basic Notions on Rule Based Expert Systems

A Rule Based Expert System (RBES) contains rules , facts and integrity con-
straints that translate the information provided by the experts. Let us describe
these items using an elementary set of rules written in bivalued logic ( α , β , γ ,
δ , ε , η , θ , ς represent propositional variables). In addition to these items, the
RBES is provided an inference engine and, possibly, a user interface .
Rule 1. α ∧¬β → γ
Rule 2. γ → δ ∨ ε
Rule 3. η →¬ε
Rule 4. δ → θ
Rule 5. ζ →¬θ
Letters like α or letters preceded by ¬β , are called literals .

Rules are implications between a literal or conjunction of literals ( antecedent ),
and a literal or disjunction of literals ( consequent ).
A potential fact is any literal that appears in at least one antecedent but in
no consequent of the rules. In our example, α, ¬β, η and ζ

¬ , like

are potential facts.