Data mining can be described as "making better use of data". Every human being is increasingly faced with unmanageable amounts of data, hence, data mining or knowledge discovery apparently affects all of us. It is therefore recognized as one of the key research areas. Ideally, we would like to develop techniques for "making better use of any kind of data for any purpose". However, we argue that this goal is too demanding yet. It may sometimes be more promising to develop techniques applicable...