SimulConsult has an interesting logic behind it. Roughly speaking, its knowledge is derived from a ‘computational wiki’ that is restricted to physician users only. So its database is not only open for viewing, but users can submit modifications to the database. The system performs bayesian pattern matching and also considers temporal information like the age of onset and disappearance of each finding for each disease under consideration.
According to Dr.Segal, there are about 33,000 data points (disease findings) in the system and the future expansion plans are to include more of metabolism and genetic diseases. Interestingly, the wiki approach for knowledge gathering in healthcare is becoming more common (AskDrWiki, WikiDoc, wikiMD to note a few- more on them later).
Feb 20, 2009 Update: Got an email today announcing that those who contribute information to SimulConsult database will now get paid for their contributions. As they are adding sponsored links in the software, I guess it makes sense to share the wealth. More info here.