There is a good article about a DSS engine: (SAGE)
P. Ram, D. Berg, S. Tu, G. Mansfield, Q. Ye, R. Abarbanel, and N. Beard, “Executing Clinical Practice Guidelines Using the SAGE Execution Engine,” Medinfo, vol. 2004, pp. 251-5, 2004
RetroGuide can model DSS logic and execute it retrospectively(with some contrains) and prospectively.
For example Ram’s example here
would looke like this in XPDL (TIBCO – for colors):
SAGE’s decision maps can be similarly represented as subflows. Rule-in and Rule-out contructs would require additional flowchart logic, but it could be generally done.