Schematism 2....

The core of a scientific theory (in the broadest Quine-Duhemian, Kuhnian, Lakatos-sense) comprises criteria for the identity of certain objects – and that respect it is like a Kantian schema. So we might learn a thing or two about the notion of a scheme from comparing it with that of that of a core.

The core of, say, classical celestial mechanics comprises the general laws of motion and a good bulk of the metaphysics associated with Newton’s Principia. Now, of course, these core assumptions specifies certain parameters pertaining to the movements of celestial objects, but these parameters also has to be connected with celestial objects if it is to be a celestial theory at all. That is, it is only by being connected with a particular planetary system that the theory can serve as a model which allows computation, prediction and the like.
This is the first lesson: a schema is applied to objects.

Now it is also clear that the empirical observations pertaining to the particular planetary system are not mere conjuncts to the axiomatic core of the theory of celestial mechanics – contrary to popular opinion neither Quine nor Duhem ever claimed this either. They are more than this: they are the points at which the theory connects with reality; the Quinian web does touch reality. Only, it must be realized that these points derive their cognitive content from the theory. That is, they don’t form independent cognitive units.
This is the second lesson: the objects subsumed under a schema do not form independent cognitive units.

The empirical observations of particular planetary systems are however not possible solely with reference to the theory of classical celestial mechanics. Astronomical observations, as a minimum, presuppose a theory of optics and of gases in order to determine the propagation of light from the celestial objects to the observer. That is, the theory of classical celestial mechanics is not applied alone.
This is the third lesson: Schemes are necessarily multiple, since they are applied never alone.

It can always be discussed how precise such a conceptual exercise of comparing two concepts is, but in this case I certainly find it helpful.