4D and databases tend to be synonymous, but the potential of 4D to represent knowledge rather than data is often overlooked. The Penny expert system shell has been used to teach artificial intelligence to Computing MSc students at the University of Surrey since 2004 and is now distributed as a compiled, cross platform 4D v12 application. This presentation will go beneath the surface of the open source Penny code to describe the algorithms on which it is based and show how it can run standalone or be used to make a conventional database smarter. It will also explore some of the underlying theory which should be of interest to any 4D developer who wants their products to stand out from the crowd!