Tough... It can be tough keeping up with all the new technologies released by Microsoft, but Windows Workflow Foundation (WF) is a technology you do not want to miss. This paper demonstrates the benefits of Windows Workflow and invites you to roll up your sleeves and get started creating your first basic workflows.

A workflow is essentially a way of documenting the activities involved in completing a unit of work. Typically, work "flows" through one or more activities during processing. These activities can be performed by either machines or by people, and can be as simple as defining the sequence of pages in an Internet application, or as complex as managing documents or products that must be seen, altered, and approved by any number of people.

Windows Workflow Foundation (WF) is a general-purpose programming framework for creating reactive programs where business rules and flow of control are represented graphically. As you shall see, the WF programming model separates the what from the when. WF is one of four technologies—along with Windows Presentation Foundation (WPF), Windows Communication Foundation (WCF), and Windows CardSpace—released by Microsoft as part of the .NET 3.0 Framework. The "3.0" designation is confusing to many developers because it seems to indicate that these technologies must be used with a new version of the .NET Framework.

From a pragmatic perspective, new technologies must be ready for prime time and provide tangible benefits before they're useful. WF hits the mark on both points. Of all the .NET 3.0 technologies, WF is the most complete in terms of functionality and design-time experience. Here are some of the benefits you reap from WF:

It provides a higher level of abstraction and visual representation of your business processes that make them easy to create and understand—both by developers and business domain experts.

It's easy to change the flow and rules associated with business processes, often without having to recompile.

WF programming encourages developers to create a core set of well-tested activities that you can reuse in multiple applications.

Compared to their UML counterpart—Activity Diagrams—WF diagrams are first-class software artifacts that don't become outdated and diverge from business process logic because they are the business process logic.

The Windows Workflow runtime provides a robust, scalable environment in which your workflows execute. For long-term processes, workflows can be persisted to a database when they become idle (optional) and reactivated when an external stimulus occurs.

Activity-Oriented Programming WF introduces .NET developers to the concept of activity-oriented programming. This programming model focuses on creating application functionality by combining sets of activities to accomplish a larger business process. As you can see in the partial workflow shown in Figure below, a workflow diagram contains activities such as validateProductActivity, sellProductActivity, backOrderProductActivity, and shipOrderActivity, each of which executes a single unit of work in a workflow.

WF and WCF make an obvious combination. Workflows will commonly need to invoke services, and implementing a service with a workflow can often be a good idea. The initial release of WF in the .NET Framework 3.0 didn’t make combining these two technologies especially easy, but the situation has improved significantly in the .NET Framework 3.5. In this version, it’s straightforward to use WF and WCF together to create workflow-enabled services. This combination depends on two new WF activities:

Send: Sends a request using WCF, then optionally waits for a response. A developer specifies the operation that should be invoked and the endpoint at which that operation can be found. The communication can use Web services or some other option that WCF provides.

Receive: Receives an incoming request via WCF, then sends a response. The developer specifies just the operation that accepts this incoming request. Receive is a composite activity, and so it implements whatever logic this operation provides through the activities it contains. This activity can be used to cause a running workflow to wait for an incoming request, or a workflow that begins with a Receive activity can have a new instance created when a request arrives. And as with Send, the communication can use Web services or another choice that WCF offers.

These two activities can be dragged and dropped into a WF workflow like any others, then configured as needed. All of the details of WCF communication—bindings, contracts, security options, and more—can be set by the workflow creator. Visual Studio 2008 makes this easier by providing a project type for creating workflow-enabled services. The intent is to allow applications to combine WF and WCF in useful ways.