ActivityDefinition is the definitional counterpart of the request resources. It is intended to describe a single activity that could be performed, and will in general result in the creation of one or more request (or "intent") resources when applied as part of a plan. The actionDefinition element of a PlanDefinition, however, is a more general description of the action to be performed. It may use an ActivityDefinition to describe the specific activity, or it may be as simple as a textual description of some action. In addition, the action level can describe relationships between actions that would be inappropriate and/or difficult to model in the ActivityDefinition. We will add this clarifying discussion to the PlanDefinition and ActivityDefinition resource documentation.