DD at a point is a measure of how many instances from different bags are
near that point and how far away the negative instances are.
The algorithm returns point(s) in feature space with high DD
For a single point target concept (t) and positive and negative bags (B), we
can find t by maximizing
If we assume a uniform prior, and that bags are conditionally independent
given the concept, then we maximize likelihood
Each bag is made up of many  instances