WF itself is a programming model, along with an engine and a set of tools for building workflowenabled applications. The programming model is made up of exposed APIs that other programming languages can use to interact with the workflow engine. These APIs are encapsulated within a namespace called System.Workflow. That namespace will be part of the WinFX programming model, but can also be installed as an add-on to the existing .NET Framework 2.0.

The easiest way to interact with the new APIs and namespace is through the Workflow Designers, which you can add onto VS2005. You must download and install WF (more on this in the next section) unless you’re using Windows Vista as your operating system. When you download and install the foundation, WF gets bolted onto the .NET Framework 2.0 and VS2005. Within VS2005, you’ll have new project types and will be able to import and use the System.Workflow namespace. The new Workflow Designer projects allow you to design workflow visually using he same drag-and-drop methods you use for creating Windows or Web-based applications. Within the designers, you build workflow much like you’d create a flowchart with a tool such as Microsoft Visio. WF also allows you to package the designers for reuse. For example, you could build a Windows application that allows business people to create their own workflow libraries. The design tools that become part of VS2005 make up the first component of the overall WF. The next component is the actual workflow. Workflow is made up of a group of activities. These activities facilitate a business process or part of a business process. Activities are a central idea within the concept of workflow and the WF. A single workflow within WF is made up of one or more activities. In the context of the WF, activities are the actual work units necessary to perform a workflow. A number of out-of-the-box activities are provided as part of the WF. These out-of-the-box activities are part of the WF base activity library. You aren’t restricted only to these activities; you can create custom activities and create your own library. You create the custom activities using the VS2005 Workflow Designers.

The next component of the WF is the WF runtime engine. The WF runtime engine executes workflow, made up of activities, and created with the VS2005 Workflow Designers. The runtime engine also includes services such as scheduling, state management, and rules. The scheduling service schedules the execution of activities within a given workflow. The state management service allows the state of a workflow to be persisted, instead of storing that state in another mechanism, such as a database. The rules service executes Policy activities. You can create workflows that are based on business rules and that perform some action when those rules are satisfied. The rules service handles all this. The last component of WF is a host process. WF itself doesn’t have an executable environment. Instead, another process must host the runtime engine and workflows. This host process may be a Windows application or an ASP.NET application. During development, this host process is VS2005. The soon-to-be-released Microsoft Office 12 can also be a host for a workflow created with WF.

Source of Information : Apress Foundations of WF An Introduction to Windows Workflow Foundation


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