Leaf nodes of the tree contain metadata describing the data associated to the node.
In order to help application developers, who are using the specification, it makes a distinction between three types of signals -
sensor,
actuator - and
attribute.
The difference between sensors/actuators and attributes is that sensors/actuators typically have
a publisher (or producer) that updates the signal value continuously when a change occur while an
attribute has a set value that should typically not change more than once per ignition cycle.
Examples and more information you’ll find in the Sensors & Actuators chapter and Attributes chapter.