The current (still limited) use of the notion of informativeness in the domain of information system ontologies seems to indicate that such ontologies are informative if and only if they are understandable for their final recipients. This paper aims at discussing some theoretical issues emerging from that use which, as we will see, connects the informativeness of information system ontologies to their representational primitives, domains of knowledge, and final recipients. Firstly, we maintain that informativeness interacts not only with the actual (...) representational primitives, but also with their variability over time. Secondly, we discuss the correspondence between representational primitives and domains of knowledge of those ontologies. Finally, we explore the possibility of an epistemological discrepancy between human beings and software systems on the understanding of ontological contents. (shrink)