Sharepoint Workflow setState externally
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i am new to the whole sharepoint world, but i have a question about sharepoint workflows. Is it possible that the workflow reacts on external events? I have something in mind like a webservice call to set the state of the current workflow. 

Background:
I have two systems, the workflow and an external one. The workflow collects the user data and submits this data to the external system. After the external System is ready, the workflow continues. 
So is it possible that the external system can "send" data to the workflow to show the current state of the whole process?

Thanks!