As pointed out earlier, the MDA especially pays off when the transformation process is not trivial, or when the transformation is well-known but involves much work. In the example given in this chapter, both situations are present. The UML-Relational mapping is worthwhile because it speeds up the process. The UML-EJB mapping is clearly a non-trivial mapping, where the transformation rules supply much knowledge of the platform.
In general, we can say that when the structures of the source and target language differ greatly, the transformation becomes more complex. Small changes in the source model may have a huge impact on the structure of the target models and thus on the implementation code.
The process of implementing a PIM is greatly improved by the application of MDA in terms of quality, because we are forced to specify transformation definitions that are generally applicable .