I. INTRODUCTION
In spite of the broad applicability of artificial immune systems (AIS) to innumerable domains, the field is only now, around 15 years after its “birth date”, receiving a more careful attention from a theoretical and formal perspective. Y. Ishida and collaborators edited the first book in the year 1998 on immune-based systems. This text was written in Japanese, what considerably restricted its diffusion. In early 1999, another volume [2] with a collection of papers on theoretical immunology and artificial immune systems was edited.