Interesting Distinction Between BizTalk 2006 and Workflow

I've been working with Workflow Foundation quite a bit lately and even had the opportunity to be teaching it to my design team at work about it's intricacies (which has been a lot of fun as well).

Coming from a BizTalk background also makes it exciting to see the differences between it and WF and how they are similar. Something neat about BizTalk is its use of Send Ports and Send Groups, which allows multiple services to be informed of an event within an orchestration (the equivalent to a sequential workflow in WF). With a send port, I could theoretically have multiple instances of the same type of service with small differences between the two and use correlation to deal with events back from multiple data sources.

However in WF, it isn't quite the same. Given everything is interface driven that is what the WF Runtime is looking at, so if I try to add multiple services of the same interface to the DataExchangeService an exception is thrown with the following message

"An instance of ExternalDataExchangeService of type TestWorkflowApp.IApproverService already exists in the runtime container."

The code that I used to do this is pretty simple. I created another class (although it would appear I could just instantiate another instance of my ApproverService class) which was the exact same implementation (just a different name). Then tried to add both to the Data Exchange Service as so

dataExchangeService.AddService(approverService);
dataExchangeService.AddService(secondApproverService);

Exception thrown.

I suppose there should be some major distinctions in capability between a free product that is part of the framework like Workflow vs. a 25k+ product like BizTalk. Certainly BizTalk offers much more than a workflow runtime (far beyond the scope of this blog) but thought it was important to point out some differences.