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Figure 26-1.

An empty sequential workflow diagram designer

The WF Runtime

Given the fact that a WF diagram equates to real types and custom code, the next thing to under-

stand is that the WF API also consists of a runtime engine to load, execute, unload, and in other

ways manipulate a workflow process. The WF runtime engine can be hosted within any .NET appli-

cation domain; however, be aware that a single application domain can only have one running

instance of the WF engine. 

Recall from Chapter 17 that an AppDomain is a partition within a Win32 process that plays

host to a .NET application and any external code libraries. As such, the WF engine can be embed-

ded within a simple console program, a GUI desktop application (Windows Forms or Windows

Presentation Foundation [WPF]), or exposed from a WCF service or XML web service.

If you are modeling a business process that needs to be used by a wide variety of systems, you

also have the option of authoring your WF within a C# Class Library project. In this way, new appli-

cations can simply reference your *.dll to reuse a predefined collection of business processes. This

is obviously helpful in that you would not want to have to re-create the same WF multiple times.

In any case, at this point understand that the WF API provides a full-blown object model that

allows you to programmatically interact with the runtime engine as well as the workflows you have

designed.