Stock market trading is an application domain with a big potential for data min-
ing. In effect, the existence of an enormous amount of historical data suggests
that data mining can provide a competitive advantage over human inspection of
this data. On the other hand there are authors claiming that the markets adapt
so rapidly in terms of price adjustments that there is no space to obtain profits
in a consistent way. This is usually known as the efficient markets hypothesis.
This theory has been successively replaced by more relaxed versions that leave
some space for trading opportunities.