An automated symptom diagnosing program

I just came across an automated symptom diagnosing program at WebMD.

http://symptoms.webmd.com/default.htm#/

I am very interested in the technology behind it, e.g., the logic inference engine, how medical knowledge is represented to computers.

If you know someone at WebMD or have connections with them, please let me know. I will study this after I am done with my PhD thesis.