Era 07 / 15 · Expert Systems 1980–1987

Expert Systems

Bottle human expertise as IF–THEN rules — a brief boom.

Beat 1 · Concrete

A consult, rule by rule

Symptoms enter on the left; rules fire down a chain — IF this AND that, THEN — until a diagnosis emerges.

A MYCIN-style consultation firing down a rule chain Four patient symptoms on the left feed into a vertical chain of three IF–THEN rule cards in the centre. A glowing pulse travels down the chain: each rule lights amber as it fires, deriving a new fact that feeds the next rule, until a diagnosis card on the right lands in chartreuse — bacterial meningitis, treat. The cascade of firing rules is the whole mechanism. fever stiff neck headache photophobia SYMPTOMS IN IF fever ∧ stiff neck THEN CNS infection IF CNS infection ∧ headache THEN meningitis IF meningitis ∧ photophobia THEN bacterial BACTERIAL MENINGITIS DIAGNOSIS
symptoms & rule mechanism a rule firing diagnosis reached motion reduced — chain frozen at the diagnosis

Beat 2 · Abstract

The rule base, as a graph

Strip the consult away: it is just conditions lighting a path to one conclusion. Same firing, no patient.

The rule base as a firing graph Condition nodes across the top connect through two AND-rule gates to two conclusion leaves at the bottom. One path lights amber — fever, stiff neck and headache feed the meningitis rule — and its leaf turns chartreuse, while the unfired measles path stays grey. The same IF–THEN mechanism as the consult, stripped to nodes and edges. fever stiff neck head- ache rash RULE ∧ AND RULE ∧ AND MENINGITIS measles
the path that fires the conclusion it reaches rules left unfired motion reduced — frozen with the meningitis path lit

Beat 3 · Interactive

Run the consult — then break it

Toggle symptoms; watch rules fire to a verdict. Then feed an unseen sign — no rule matches, and it stalls.

fever stiff neck headache rash unseen sign IF fever ∧ stiff neck THEN CNS infection IF CNS infection ∧ headache THEN meningitis IF fever ∧ rash THEN measles VERDICT awaiting input select symptoms above

Toggle symptoms to run the consult

Static example of a fired rule chain With JavaScript enabled this becomes interactive. Shown statically: fever, stiff neck and headache fire two rules to a confident chartreuse verdict of bacterial meningitis; an unseen sign would instead stall in coral. 3 symptoms on → 2 rules fire → BACTERIAL MENINGITIS
symptom active rule fired / confident diagnosis no rule matches — stalled
The boom, in three names
MYCIN · DENDRAL
The first experts
Stanford's DENDRAL (chemistry) and MYCIN (~600 rules for blood infections) proved rules could rival specialists — yet were never deployed clinically.
XCON / R1 · DEC
The money case
Digital's XCON configured VAX orders from thousands of rules, reportedly saving ~$25M a year — the proof that expert systems paid.
The bottleneck
Knowledge acquisition
Every rule had to be hand-extracted from an expert. Rule bases grew brittle and unmaintainable — the wall the Second Winter ran into.