Windows Workflow Foundation: Support for Workflow-Based Applications

A workflow is a simple idea: it’s just a series of steps performed in some order. One might even argue that every application implements a workflow, since every application executes some process. Yet the traditional approach to creating an application using C# or Visual Basic or some other programming language is to make the steps in this process implicit in the code. This certainly works, but it also embeds the process itself deeply into a program’s logic, making that process more difficult to create and to change.
Using workflow technology to implement process logic can be an effective way to address this problem. Rather than intertwining the logic in ordinary code, each step in the process is explicitly defined, then executed by a workflow engine. The result is a clean implementation of the process itself. With Windows Workflow Foundation (WF), Microsoft provides a common workflow technology for Windows, giving any workflow-based application a common foundation to build on. Since its release in the .NET Framework 3.0, WF has been used both in software provided by Microsoft, such as Windows SharePoint Services, and in applications created by other organizations.
But how can a single technology meet the diverse set of requirements presented by different workflow applications? The answer adopted by WF is to take a very general view of workflow.
a WF workflow is just a group of activities that are executed by the WF engine in some order. Each activity is actually a class, and it can contain any work that the workflow’s creator deems necessary. Activities can potentially be reused across different workflows, making it easier to create automated solutions to new problems.