An Actionable Attribute defines the active property of a ThingFacets or AppFacets. Any attribute which has a modifier "KnownBy" an Action, or multiiple Actions, is called an actionable attribute. An actionable attribute will activate the associated Action(s) whenever its value is modified.
Like for any attribute,
An attribute "KnownBy" an action becomes an actionable attribute. Any changes in the actionable attribute value will activate the corresponding action by creating an instance of that defined action. And this is the only way an action can be activated.
All attributes have both values ("value") and known values ("known"). Known values are only updated by messages received from outside the application, such as from a sensor or a machine. Values are only updated by the application itself. More on values and known values, see here.
In an attribute-action pair, either a change to the "value" or a change to the "known" will trigger the action.
Relationship between Actionable attributes and actions