I solved many challenging problems, e.g. I wrote a parser generator, that can generate itself, I wrote an UN/EDIFACT parser that was parsing the human readable UN standard to create a parser for a semantic translation. My Y2K PTFs run on every MVS and OS/360 system. I did a lot of machine learning in the last 10 years, e.g. optimizing maintenance of Siemens power plant turbines or quality control for injection molding machines.

But ... I'm taking the biggest challenge right now. I'm coding my Onyx database client idea for 3rd time. The hardest problem was to start o3db. I failed badly with Onyx 20 years ago by burnout holding over half a million lines of C++ in flow together with nearly 10k lines of my own 4gl, during the 3rd customer installation of Onyx. I was very shy of coding UI/UX afterwards, escaped deep into server stuff, machine learning - escaped as far away from user as possible.

So, my biggest challenge was to start Onyx again: A user facing UI/UX for common business database applications with its own fourth generation language. I've decided for Scheme as an intermediate language this time, and the prototype running well. I now have a non recursive Scheme interpreter and GUI running in browser, able to process the meta tables defining an application. Its still a long road to my vision. But to start a project again, I failed with a burnout 20 years ago, and to code it with actual technology, was the biggest personal challenge.

/join #o3db on freenode, if interested in a startup to create common business database clients for the web.