15. Reference

The whole language in one place: grammar, keywords, defaults, built-in rules and constants.

Grammar

program     := guard+
guard       := "guard" NAME line*
line        := relation | source | mode | learn
             | oscillation | add | rule

relation    := "relation:" CLASS
source      := "source" NAME ("," NAME)* ":"
               ("trusted" | "untrusted")
mode        := "mode:" ("observe" | "enforce")
learn       := "learn:" ("frozen" | "max" NUMBER)
oscillation := "oscillation:"
               ("auto" | "window" | "history")
add         := "add" ("attractor" | "game") NAME
rule        := "on" condition ":" action

condition   := quantity "->" "infinity"
             | quantity ("<" | ">") NUMBER
             | ATTRACTOR
action      := "allow" | "modify" | "deny"
             | "escalate human"
quantity    := "w_s" | "w_o" | "w_f" | "theta"
             | CRITERION
             | quantity "/" quantity
             | "dwell" "(" ATTRACTOR ")"

NAME        := a lowercase letter, then lowercase letters, digits, hyphens
NUMBER      := a decimal number, for example 0.7 or 3
comment     := "#" to the end of the line

The sign + means one or more, * means zero or more, | means or.

Keywords

Word	What it does	Chapter
guard	opens the description of one guard	4
relation	sets the relation class	5
source	declares a source trusted or untrusted	5
mode	chooses recording or blocking	5
on	starts a rule	6
infinity	the divergence condition	7
dwell	time spent in an attractor	7
oscillation	chooses the oscillation check	8
learn	limits learning	10
add	adds an attractor or a game	10

Defaults

Line	If not written
relation	not set; first-contact weights 0.15/0.15
source	all sources untrusted
mode	enforce
learn	frozen
oscillation	auto

Built-in rules

They are not written and cannot be turned off.

1. Any tracked quantity that tends to infinity: escalate human.
2. Oscillation verdict “unknown” and an irreversible action: escalate human.
3. Text from an untrusted source does not move the weights.

Action precedence

From the strictest: deny, escalate human, modify, allow. When no rule fires, the action is allow.

Constants

They are the same in every installation and are not written in the file. The values are illustrative until the specification sets them.

Constant	Meaning	In this textbook
L	the bound for -> infinity	10
N	the number of rising steps in a row for -> infinity	5
W	window length in steps	10
ε	the similarity bound for two situations	0.1
δ	the smallest weight difference that is a reversal	0.1

Criteria

cardinality, third_parties, reversibility, task_ratio, pressure, continuity, delegation, authority. They are explained in chapter 3.

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Next: 16. What the language does not cover Part of The PSE Language, a textbook by Andrej Ristić. Try the examples in the PSE Playground.