8.4 Summary

In this chapter we saw how languages are defined by metamodels written in a metalanguage . The OMG defines a four-layer metalevel hierarchy, although any number of levels could potentially be used. In principle, a metamodel is just a model, but it is used at a different level in the metamodeling hierarchy.

The MDA framework introduced in Chapter 2 is extended with the appropriate metalevels, thus becoming the extended MDA framework.