But here comes a crucial question, and the answer to this question will be also a justification of the title of this talk, that - as you can remember - deals with models and metamodels.
How many abstraction levels? So, this is the real world with all its software and hardware systems. Well, above this level, we have a number of meta-levels, but the important thing is that it seems appropriate to distinguish at least two meta-levels.
The semantical and syntactical formal systems that we described earlier - when I said that there's this plethora of formal systems - live on the first meta-level.
But the necessity to try and analyse these systems themselves as objects of studies, leads us to conceive yet another semantical level.
This is the higher meta-level of metamodels.
It is at this level that we discuss meta-theorethic properties, and we develop tools for manipulating the system which live at the first meta-level.