Again and again I meet people do not know at what abstraction level we just discussed. OMG's 4 level meta architecture is a good description of abstraction level in model driven software development environments. The following diagram provides an overview of meta level and some modeling technologies.

The meta-metamodel level (M3) includes the notation for meta modeling. The metamodel level (M2) includes the notation for modeling (domain specific language). The model level (M1) includes the system design. And the instance level (M0) includes "possible" run-time data.