6. Rules

A rule says: when the condition is true, take the action. The shape is always the same:

on CONDITION: ACTION

Four actions

Action	What the guard does with the step
allow	lets it through unchanged
modify	lets it through in a changed, narrower form
escalate human	holds it until a human decides
deny	refuses it

What exactly the change looks like under modify is set by the guard interface, not by the language.

Three kinds of condition

Comparison with a number. A quantity, the sign < or >, a number.

guard support
  relation: customer-service
  on pressure > 0.7: modify
  on authority > 0.8: deny

Only < and > exist. Both are strict: pressure > 0.7 is not true when pressure is exactly 0.7.

An attractor name. The condition is true while the agent is in that attractor.

guard support
  on borderline: escalate human

Divergence. A quantity, the arrow ->, the word infinity. This is the subject of chapter 7.

guard payments
  on w_o / w_s -> infinity: escalate human

What can be a quantity

• the weights and θ: w_s, w_o, w_f, theta
• each of the eight criteria, for example pressure
• a ratio of two quantities: w_o / w_s
• time spent in an attractor: dwell(borderline)

In a rule the weights are read. They cannot be set.

When several rules fire

In every step the guard checks all rules. The order they are written in does not matter. If several fire, the strictest action applies:

deny, then escalate human, then modify, then allow.

If none fires, the action is allow.

Step-by-step trace

Guard support with the two rules above, four steps:

Step	pressure	authority	Fired	Action
1	0.30	0.10	nothing	allow
2	0.75	0.20	first rule	modify
3	0.80	0.85	both rules	deny
4	0.70	0.80	nothing	allow

In step 3 both rules fire, so the stricter one wins. In step 4 both values sit exactly on the threshold, and a threshold has to be passed.

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Next: 7. infinity Part of The PSE Language, a textbook by Andrej Ristić. Try the examples in the PSE Playground.