Plan and schedule

Projects, plans, schedules and deadlines. These are the language of business. PML, as we have seen is well adapted to recording events in the physical world. It is less well suited to communicate intended events - particularly by human parties. In part this is due to the intended ambiguity introduced into human communication.

The Physical Markup Language strives to precise and umbiguous communication. Given these constraints, however, we can define components to communicate future events - in particular plans and schedules.

Since a plan is a sequence of events - or more precisely a set of events whose execution is predicated on the completion of a preceding event - we need to encapsulte the properties of an "event." Therefore we introduce a base component, which we will call a task .

In general a task requires resources . These resources may be human, machine or material. We will include these resources in the definition of the task. Fortunately, we have already introduced definitions for humans (entities), objects (EPC and PML) and to some extent machines (EPCs). These will be included definition of the task.

The execution of a task depends on many things. Are the resources available? Is it appropriate to execute the task? Is the task in fact required? Has the task already been complete? All these circumstances and dependences we will simply call a context . If the context is satisfied, the task will execute.

A task has a stated objective. Paint the fence. Write the report. Order the part. All of these have a well defined end point. We call this end point the goal or objective of the task.

Often a task is further subdivided into smaller tasks or subtasks . These subtask in turn are divided into even smaller tasks. Tasks and subtask form the structure of a tree.

So we have identified a task with resources, context and a goal, as well as a tree structure of tasks and subtasks. Since resources are required to execute the task, these will be included in the definition of the task. Thus a task will include a context and goal. This forms the basis for our definition of plans and schedule.