A general scheme for dealing with ontological issues form a "Scientistic point of view" is proposed. "Ontological commitments' (in Quine's sense) should always be examined with respect to a well-established scientific theory. By means of a schematic example of "reconstruction" of a piece of experience within a theoretical frame, it is shown what the essential steps in the process of constructing of a scientific ontology are. This steps involve, first, the construction of a "model of data" for a given "experiential situation", second, the selection of a model of a mathematized theory, an third, the subsumption of the data model under the selected mathematical model. A further schematic example provides the clues for answering the question of ontological reduction between different experiential domains. A final word is said about what it would mean to have a really unified universal ontology.