Over the years, I've done hundreds of data migrations between the databases of a few competing products. I mean databases that, to a large degree, have similar domains and purposes, but which differ (often dramatically) in design and implementation. I'm used to doing conversions both manually (using queries and mapping tables) and writing automated tools for systems I deal with frequently.
However, I realized that I have little knowledge of tools and techniques outside my own bubble of experience. A Google search showed many products, a lot of which focus on migrating databases between DBMSs while keeping schema intact. Also, I'm skeptical of any claims of quick and pain-free conversions.
What's the state of the art, guys? Are there universal converters which can take a mapping between data dictionaries and handle the data automatically? Is it feasible to write a universal converter for a given target system? Any recommended products - commercial or otherwise?