MSDN Magazine - January 2009 - (Page 51)

between WCF and WF leaves something to be desired. In the WCF Service .NET Framework 3.5, the WCF artifacts have to be defined and WCF Work ow configured using the WCF programming and configuration model, while the workflow is defined using a different model. WCF Endpoint Ultimately, you end up with multiple artifacts that need to be External Client deployed, configured, and managed separately. Service Another reason for the difficulty is that the current base WCF Endpoint activity library concentrates on flow-control and logic activiExternal ties and doesn’t provide much in the way of work activities. So Service you must write a library of custom activities before you can implement real-world workflow services with WF. Given the complexity of that job, some developers have given up before Figure 1 WCF Workflow Services they are able to experience the benefits of WF. In addition to these issues, current WF also lacks tool support for eXtensible Application Markup Language (XAML)-on- gramming model for custom activities, a new flowchart workflow ly workflows, which are also referred to as declarative workflows type, and numerous WCF-specific improvements. because they’re completely described in an XML file without any codebehind files. The XAML-only approach creates some compel- WF Base Activity Library ling workflow hosting and deployment possibilities. The powerful The .NET Framework 4.0 comes with an enhanced base activity thing about a declarative workflow is that it’s just data that can be library containing several new activities (see Figure 2). Microsoft stored anywhere and executed within a WF runtime environment also plans to begin making additional WF activities available through that knows about the activities being used. CodePlex between major .NET Framework releases. You’ll also beA declarative workflow can be deployed to a runtime in the cloud gin to see more work activities (such as the PowerShellCommand or to a workstation under your desk (assuming the activities have activity) appear in future releases (or on CodePlex), thereby reducbeen deployed to the runtime host). Declarative workflows are also ing the need for custom activity development. And because Microeasier to version, and they can be used in partial-trust scenarios soft is using CodePlex, you have a good opportunity to make your (think “cloud”). The XAML-only model is also easier to build tools opinion heard on what additional activities you’d like to see. around since the tools are just working with XML files. The .NET Framework 4.0 introduces a few core activities that In general, the XAML-only model has always been the ultimate provide more flow-control options, including the FlowChart, Forvision for WF as a technology, which is evident in the early writings Each, DoWhile, and Break activities. The new FlowChart activity is by its architects. However, the current WF tool support doesn’t fully realize that vi- Figure 2 New WF Activities in the .NET Framework 4.0 sion. While it’s possible to build XAML- Activity type Description only workflows with the .NET Framework FlowChart Flow Control Executes contained activities using the familiar 3.5, you have to work around the current flowchart paradigm. Visual Studio templates and give up im- ForEach Flow Control Executes a collection of activities in sequence. portant features, such as debugging. Flow Control Pauses workflow execution by creating an outstanding Break The main goal for WCF and WF in the Bookmark. .NET Framework 4.0 is to simplify the DoWhile Flow Control Executes the contained activities once and continues to developer experience around declarative do so while a condition is true. workflows and services, fully embracing a PowershellCommand Windows Powershell Executes a command in the Windows Powershell XAML-only model. In addition, Microenvironment. soft wanted to take things one step further sendMessage WCF sends a one-way message through WCF. by making it possible to define declara- receiveMessage WCF Waits for a one-way message to arrive through WCF. tive workflow services. That is, WCF ser- Clientoperation WCF Builds on sendMessage/receiveMessage to invoke a vices that are completely defined in terms WCF operation. of XAML, including the service contract serviceoperation WCF Builds on receiveMessage/sendMessage to expose a definitions, endpoint configurations, and WCF operation. the actual service implementation (in the Correlationscope WCF Defines a scope for correlating multiple WCF messages. form of a XAML-based workflow). initializeCorrelation WCF Allows you to establish a correlation value in advance. To accomplish this, Microsoft has made Assign runtime Assigns a value to a workflow-level variable. numerous improvements in the .NET Methodinvoke runtime Executes a method of a CLr object. Framework 4.0, including an extended Persist runtime Explicitly requests that the workflow persist its state. base class activity library, a simpler promsdnmagazine.com January 2009 51 http://www.msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2009

Toolbox CLR Inside Out Basic Instincts Cutting Edge Test Run First Look� Geneva Framework Silverlight Windows Mobile Service Station Security Briefs Extreme ASP.NET Foundations .NET Matters { End Bracket }

MSDN Magazine - January 2009

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