rule

The rule keyword is used in TypeQL schema to define a rule for rule-based inference.

Syntax

The syntax of a plays statement includes:

header — the rule keyword followed by a rule label and a colon
condition — the when keyword followed by a condition pattern in curly brackets
conclusion — the then keyword followed by a conclusion pattern in curly brackets

Syntax

rule <rule-label>: when {
    <condition>
} then {
    <conclusion>
};

Behavior

TypeQL statements with the rule keyword can be used only in Define queries. To undefine a rule, use the rule keyword, followed by the rule’s label, and a semicolon.

The rule keyword adds a new rule to a schema, or updates an existing rule with the same label.

Usage in a schema definition

For this example, use a database with the IAM schema and sample data loaded.

Usually, Define and Undefine queries you can’t use variables. But rules use patterns for matching data in their condition and conclusion.

A condition of a rule can be any pattern, similar to a match clause.

A conclusion of a rule can be a single statement: either a has statement, or an isa statement for a relation with any number of roles.

For example, to define the add-view-permission rule, that adds a permission for a subject to view a file if there is one to modify it, use:

Define a rule query example

define
rule add-view-permission: when {
    $modify isa action, has name "modify_file";
    $view isa action, has name "view_file";
    $ac_modify (object: $obj, action: $modify) isa access;
    $ac_view (object: $obj, action: $view) isa access;
    (subject: $subj, access: $ac_modify) isa permission;
} then {
    (subject: $subj, access: $ac_view) isa permission;
};

To remove the new rule, use:

Undefine rule query example