Few words are used with so many different meanings as the term "model." In
everyday language the word "model" can be applied in a moral, fashion, economic,
linguistic, or scientific context; in each case it means something completely different.
Even if we restrict ourselves to the category of scientific models, the notion is
ambiguous, because it could signify the reproduction in miniature of a certain physical
phenomenon, and at the same time present a theoretical description of its
nature that preserves the broad outline of its behavior. It is the theoretical aspect
of models that we wish to consider; in order to emphasize this, we describe this type
of model as "mathematical" (Tarski 1953). Formulating a mathematical model is a
logical operation consisting in: (i) making a selection of variables relevant to the
problem; (ii) postulating statements of a general law in precise mathematical form,
establishing relations between some variables said to be data and others unknown;
and (iii) carrying out the treatment of the mathematical problem to make the connections
between these variables explicit.