PlanFrames

Task Frame Notation

The purpose of a Plan Frame is to describe part of a process. A component of the system called the Planner creates programs, called plan trees, by assembling related Task Frames. The Planner assembles task frames to form a plan. It does that by working backwards from a goal. The goal matches a post-condition in one of the task frames.

The notation of the task frame is designed to concisely describe an individual task. It also facilitates starting with an end-goal and then letting the system identify what process knowledge remains to be described.

Syntax

---
Task: (imperative sentence - is the name/title of the task)
Post: (declarative sentence)
Pre:
. (pre-condition - matches some other task's post-condition)
. (pre-condition)
. (...)
. (Some tasks have no pre-conditions. They are ready to run.)
Actions:
. (role) : (action - understood by an actor assigned the role)
. (role) : (action)
. (...)
. (Some tasks will have no actions. They simply define a named-state.)
---

Example

Task: Deliver order to customer.
Post: Order delivered to customer.
Pre:
. Customer has paid for order.
. Order is ready for delivery.
Actions:
. Counter: Give order package to customer.
. Bookkeeper: Account for order revenue and taxes.

Task Frame Statements

• The "Task" statement identifies the task. It gives the task a name for reference.
• The "Post" statement defines the post-condition that will be satisfied when the task is completed. The post-condition of the top-most task in a plan tree is the goal of the plan.
• The "Pre" statements define the pre-conditions that must be met before work on the "Actions" can begin. Some task frames have no pre-conditions which means that the work can begin immediately.
  - The Planner forms a plan tree by back-chaining pre-conditions in each frame to post-conditions in other frames until all the pre-conditions are matched.
• The "Actions" specify the work needed to satisfy the post-condition once the pre-conditions have been satisfied. Some task frames have no actions. Such frames serve to combine two or more conditions into a single condition.