Abstract

Complex systems are omnipresent. Everywhere in the real world we can see them. First of all in biology, a living cell, the genetic system, the brain are complex systems. But there are lots of complex systems of different kind. A galaxy, a financial market, an ants colony, Internet, a supply chain are also complex systems. They are in general not easy to understand because they are made up of many components interacting not linearly. Their global behaviour is difficult to predict because it results from the many local interactions of their components. Frequently this behaviour is surprising and counter intuitive even though it is the simple consequence of these interactions: It seems that from the mere consideration of these interactions it is not possible to deduce the behaviour actually observed. This is the so called "emerging behaviour". One can also speak of the "emerging properties" of a complex system. Beyond this simple intuition, the concept of emergence is not so easy to define because, though not very recent, it can be understood in different acceptation more or less objective