The aim of the present volume was to give an overview over different available methodological approaches. The specialists may, perhaps, object that in their particular field the level of information is superficial. However, let them look at other chapters in which different approaches are discussed and which, surely, will appear less superficial from the more general point of view. We hope, at least, that crucial references can be traced throughout the book that would enable the readers to go in more detail when desired. It can be traced throughout the book that would enable the readers to go in more detail when desired. It was really one of our ideas to draw the survey of possibilities available. If this can stimulate the readers to use ideas to draw the survey of possibilities available. If this can stimulate the readers to use other methods that those they are routinely using the goals will be met.