There have been some attempts to do this sort of thing, either with Dia, or with
SQL Fairy using an open XML format. The tricky thing here is that first you need to have a good graphical UML tool that can generate something that your code generator can work with.
This would not have much to do with MakeMaker or h2xs though. The former is an installation system and the latter is a helper for integrating C code. Some people do suggest using h2xs to create stubs for pure perl modules, but the results are not very good (bizarre file layout).
