.NET - Windows Workflow Foundation

In addition to the standard activities available within the base activity library, you can create new activities to meet specific business needs. Creating custom activities may be required to support a particular application that you want to integrate with WF. Custom activities are generally created through attributes and inheritance. You can create two types of custom activities, base and composite. You can create basic custom activity by inheriting the Activity class and custom composite activity by inheriting the compositeActivity class or a derived type.

Dynamic update is a powerful feature of WF that describes the ability of WF to modify the execution path of a running workflow. This feature is used in circumstances that call for extraneous behavior that was not modeled by the original workflow developer.

A runtime engine of WF provides the basic functionality to execute and manage the workflow lifetime. It runs within the host process and is responsible for executing each workflow instance. A host process can interact with multiple runtime engines at a time, where each engine executes multiple workflow instances. The host process interacts with runtime engine by using any of the following classes:

• WorkflowInvoker - Invokes a workflow as its method.
• WorkflowApplication - Controls the execution of a single workflow instance explicitly.
• WorkflowServiceHost - Hosts the workflows and allows sending and receiving messages among various instances of workflows.

In Windows Workflow Foundation 4.0, an activity is the basic unit of composition and execution of a workflow. Each activity in a workflow consists of its own variables and arguments and is a subclass of the Activity class. These activities provide facilities for flow control, exception handling, data persistency, loading or unloading workflows, tracking, and transaction flow.