"Simulation of any system implies a mapping from observable aspects of the system to corresponding symbolic elements of the simulation." (H. H. Pattee, "Simulations, Realizations, and Theories of Life", in Artificial Life) For Pattee, realizations are functional replacements. They are judged primarily by how well they function as implementations of design specifications. (Thus a building would be the implementation of a blueprint)
"The study of dynamical systems by computer often blurs the distinction between theories and simulations." We could call this SimScience -- the use of fractals in the earth sciences, for example, undescores the differences between simulation and inferences about process, between description and explanation.
what is the relation between simulation and representation?
"Produced by a code or linguistic form that does not really refer but merely simulates reference, the simulacrum is the image or the reproduction that testifies to the short-circuiting of reference in postmodernism." (Simpson, Time, Technology, and the Conversations of Modernity.), p.138)
see virtual reality as the simulation of embodied presence.