Where are We?

With a few C# classes and a little XAML, we have illustrated the central aspects of the WF programming model. It is easy to develop activities, such as PrintKey and ReadLine, that function as domain-specific program statements in WF programs. Activities like ReadLine use bookmarks (WF program queues) to wait for external stimulus. Composite activities like Sequence provide control flow for WF programs and also rely upon (internally managed) bookmarks. A WF program can be expressed declaratively in XAML, and the structure of the markup conveys the control flow of the program. The execution of a WF program instance is episodic and can span machine boundaries. The WF runtime, which is responsible for managing WF program instances, can be loaded in any CLR application domain by creating an object of type WorkflowRuntime. The addition of a persistence service allows the WF runtime to passivate idle WF program instances.

We've taken a quick tour of the WF programming model, so you should now be getting a feel for the kinds of solutions you can build with Windows Workflow Foundation. In the remainder of the book, we will take a much closer look at specific aspects of activities, WF programs, and the WF runtime. We'll begin in the next chapter by returning to and elaborating upon the ideaintroduced in Chapter 1of an automaton that describes the lifecycle of an activity.