Sequential Workflows

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Sequential Workflows and State Machine Workflows

WF provides support for modeling two flavors of a business process workflow: sequential workflows and state machine workflows. Ultimately, both categories are constructed by piecing together any number of related activities. However, how they execute is what sets them apart.

Sequential is the most straightforward workflow type. As its name implies, a sequential workflow enables you to model a business process where each activity executes in sequence until the final activity completes. This is not to say that a sequential workflow is necessarily liner or predictable. It is entirely possible to build a sequential workflow that contains various branching and looping activities, as well as a set of activities that execute in parallel on separate threads. The key aspect of a sequential workflow is that it has crystal-clear beginning and ending points.

Consider the following simple sequential WF. Note the clear starting point (green circle containing an arrow at the top) and end point (red square containing a circle at the bottom) embedded within the designer.

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In contrast to sequential workflows, state machine workflows do not model activities using a linear path. Instead, the workflow defines a number of states and a set of related events that trigger transitions between these states.

Consider this state machine WF diagram, which represents the processing of an order. Notice that each state in the workflow can flow across various states based on some external event. For example, the OrderOpenState state can listen for two events (OnOrderUpdated and OnOrderProcessed). When these events occur, there is a state transition. You will learn about state machine workflows later in this class.

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