Process Execution Model Overview

The process execution model defines the structure of a workflow, and has several process steps that can be programmed and triggered during a workflow instance.

All workflows are process-oriented. A workflow is a representation of what happens as the result of executing the process. It is made up of subprocesses, which are made up of activities. A subprocess is a grouping of activities that accomplish a specific outcome. An activity is a single logical action within a subprocess and is the smallest unit of work that can be performed within a process.

A scheduled task contains all necessary information about the process to enable it to be executed by the workflow execution engine. A scheduled task specifies when a process begins (that is, when it enters a run-time state, or becomes a workflow instance), the event that triggers it, who the instance is assigned to, the specific location it must be performed, or what inputs/outputs are required.

When the workflow definition begins running, the load step starts and any activities within this step run. After the load step runs, the preprocess step is triggered, which begins the process event cycle.

When the preprocess step finishes, the body of the process begins. The body consists of the presubprocess and postsubprocess steps, as well as a subprocess and flow control activities such as If/Else and Parallel activities. A process can also consist of one or many subprocesses and each subprocess has zero or more activities grouped together within it. The cycle of presubprocess, subprocess, and postsubprocess run until all the subprocesses within the process are complete. The postprocess step begins after the last subprocess ends. When the postprocess step ends, the unload step begins. When this step finishes running, the workflow instance ends.