I will be speaking at VSLive! San Francisco on February 25 on "Advanced Topics in Windows Workflow Foundation".

The conference will be at the Hyatt Regency Embarcadero from February 23-27. Workshops are offered on Feb 23 and 27. The conference sessions are on Feb 24, 25 and 26. If you register with promo code NS9F20 you will receive a $500 discount off the price. The event web site is vslive.com/2009/sf.

There is some great content that covers ALM and Development Tools, .NET, Data Management, Infrastructure, Rich Clients, Distributed Systems, and Web Development. I hope to see you there.

"this is a well-known problem with code files that have desigable classes in them - the class that is to be designed has to be the first class in the file.  If you do the same thing in windows forms you get the following error: the class Form1 can be designed, but is not the first class in the file. Visual Studio requires that designers use the first class in the file. Move the class code so that it is the first class in the file and try loading the designer again."

It turns out I had changed a struct that was defined first in my file to a class. I moved that class to the end of the file and "mirabile dictu" everything worked.

So if this is a well known problem, why can't we get an error message just like in the Windows Forms case?

While it was clearly my mistake, Microsoft has a share of the blame here. Clearly this requirement makes it easier to build the workflow designer. It would have been just as easy to check if this class was not defined first, and issue an error message.

The Windows Workflow Foundation (WF) ships with a Policy Activity that allows you to execute a set of rules against your workflow. This activity contains a design time rules editor that allows you to create a set of rules. At run time, the Policy Activity runs these rules using the WF Rules engine.

Among other features, the rules engine allows you to prioritize rules and to set a chaining policy to govern rules evaluation.  The rules engine uses a set of Code DOM expressions to represent the rules. These rules can be run against any managed object, not just a workflow. Hence, the mechanisms of the rules engine have nothing to do with workflow. You can actually instantiate and use this rules engine without having to embed it inside of a workflow. You can use this rules engine to build rules-driven .NET applications.

I gave a talk at the last Las Vegas VSLive! that demonstrates how to do this. The first sample in the talk uses a workflow to demonstrate the power of the rules engine. The second and third samples use a very simple example to demonstrate how to use the engine outside of a workflow.

Two problems have to be solved.  You have to create a set of Code DOM expressions for the rules. You have to host the engine and supply it the rules and the object to run the rules against.

While the details are in the slides and the examples, here is the gist of the solution.

To use the rules engine at runtime, you pull the workflow rules out of some storage mechanism. The first sample uses a file. A WorkflowMarkupSerializer instance deserializes the stored rules to an instance of the RuleSet class.  A RuleValidation instance validates the rules against the type of the business object against which you will run the rules against. The Execute method on the RuleExecution class is used to invoke the rules engine and run the rules.

How do you create the rules? Ideally you would use some domain language, or domain based application, that would generate the rules as Code DOM expressions. If you were masochistic enough, you could create those expressions by hand.

As an alternative, the second sample hosts the Workflow rules editor dialog (RuleSetDialog class) to let you create the rules. Unfortunately, like the workflow designer, this is a programmer's tool, not a business analyst's tool. A WorkflowMarkupSerializer instance is used to serialize the rules to the appropriate storage.

I would be interested in hearing about how people use this engine to build rules driven applications.

My series of four digitial articles have been published by Addison-Wesley. You can get the links to purchase them and the associated source code from my web site.

I have tried to explain, in practical terms, what you need to know to actually build real world software using Windows Workflow. There is a tiny amount of theory to explain the underpinnings. The vast majority of the explanation uses code examples to illustrate all the key points. The last shortcut in the series has two extended examples that illustrate how to build custom activities.

Here are good instructions on how to install RC1 for the .NET Framework 3.0: http://blogs.msdn.com/pandrew/archive/2006/09/07/745701.aspx. People, including myself, have been having problems getting the Workflow Extensions for Visual Studio 2005 installed. I moved the installer file (Visual Studio 2005 Extensions for Windows Workflow Foundation RC5(EN).exe) to a different directory from the other installation files. The workflow extensions then installed just fine.

I have updated the workflow examples on my site to the most recent Workflow version.

Here is my final dnrTV session: http://dnrtv.com/default.aspx?showID=24. It covers advanced topics in Windows Workflow Foundation such as synchronization, transactions, and compensation.

How do workflow and service oriented architecture relate?

The real question is how service oriented architecture (SOA) and business processes relate.

Service orientation is about how to organize and utilize distributed capabilities that could be under the control of different owners.¹ Business Process Management (BPM) is about modeling, designing, deploying and managing business processes.²  Business processes are the capabilities, or the users of those capabilities. Workflow is a technology that builds the automated part of a business process. It integrates human decision with synchronous and asynchronous software systems. Of course this is somewhat recursive because a workflow could use other services in its implementation.

For me, SOA and BPM are not in conflict. People talk about layering BPM on top of SOA. Or that SOA is for IT folks, and BPM is for business people. In today's world, business cannot afford to have people who just think IT, or just think business. Given the way the human mind works, multiple models are often needed to think about certain problems.³ SOA and BPM are two different ways to think about the same problem: how organizations can best accomplish their missions. Thinking about business process will transform how you architect your services. Architecting your services will impact how you model your business processes.

¹ For more information about service oriented architecture take a look at the Reference Model that the OASIS TC that I am a member of has produced:  http://www.oasis-open.org/committees/download.php/18486/pr-2changes.pdf

² See http://ww6.infoworld.com/products/print_friendly.jsp?link=/article/06/02/20/75095_08FEbpmmap_1.html

³ See "Mental Models" by P.N. Johnson-Laird in Foundations of Cognitive Science edited by Michael I. Posner

I was interviewed by Carl Franklin and Richard Campbell on .NET Rocks: http://dotnetrocks.com/default.aspx?showID=183. Yes we talked about Workflow and SOA. But we touched on other topics such as the failure of technology to really make foreign language learning any better.

Here is part three of the Workflow Webcast series: http://dnrtv.com/default.aspx?showID=23

Here is the second talk on Workflow Foundation on Carl Franklin's dnrTV:

http://dnrtv.com/default.aspx?showID=22

Here is the first of four talks on Microsoft Windows Workflow Foundation that are appearing on Carl Franklin's dnrTV. This one was broadcast on June 2. Each of the following ones should appear in subsequent weeks.

http://dnrtv.com/default.aspx?showID=21