Since the results obtained by means of computer-based simulations have an experimental character, their validation requests their reproduction. These results are obtained by observing the outputs of the runs of a software entity, which is the concrete device of the experimentation; thus, it is this software simulation model that must support a new implementation. Although the replication of a model brings many advantages, in many cases it is problematic. This paper proposes to present simulation models as systems, to ease their replication.