I am not sure if this is the answer you are looking for but in Data Flow Diagram, you can create a data flow between Processes but not between DataStores.
Here's the link to a DFD figure I drew (Since I cannot directly post an image yet) http://changevision.files.wordpress.com/2014/04/astah_dfd.png
PS: You may want to add a DFD tag instead of uml for this question?