Ed- Thoughtful points, thank you. The way I'm imagining it, with the added input and output constructs in the jpdl, nodes could declare n "ports" that take or produce certain types of data. The code in the node, or handler I guess, would be responsible for retrieving data from an input and staging data on an output. The execution engine could then handle moving the data structures in and out of the process variable space using a naming convention that would identify them as belonging to inputs or outputs. For example, when a node would call, getInput(String portName) let's say, then some infrastructure code would look for the corresponding input in the process variable map, return the object, and remove it from the process variable map. Conversely, when a node wanted to stage an output, it would call setOutput(String portName, Object output), and infrastructure code would handle moving the data into the process variable map using the specified naming convention. Using this mechanism, I think the scenarios you describe could be prevented. But I might be missing something. Also, process variables would work just as they currently do, but would be overloaded to support data flow. Maybe this sounds a lot like a hack, but I was just brainstorming about how this could be implemented with the least amount of work up front. Your point about cluttering up the process graph is well taken. I concur that another "view" of the graph would be required specifically for the data flow to reduce the complexity. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4017702#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...