I. Introduction
Computer games today are a vibrant part of the advanced world countries' economies. According to van Eck [9], the digital game industry in the US is at 10 billion $ per year, while serious games produce an income of 20 million $. These numbers are expected to grow, since in the next years more U.S. companies will adopt serious games as part of their training efforts [17]. Also in Europe, the interest in serious games is increasing. For example, in the Netherlands, the Game Institute for Training and Entertainment (GATE) has been awarded with a 10 million euro grant
http://gate.gameresearch.nl/
.