fn Get(interface_name: string, property_name: string) {
    value: variant,
}

fn Set(interface_name: string, property_name: string, value: variant) {
}

fn GetAll(interface_name: string) {
    props: array(dict(string, variant)),
}

sig PropertiesChanged {
    interface_name: string,
    changed_properties: array(dict(string, variant)),
    invalidated_properties: array(string),
}