And this I think is best not done in SQL/ the relational-data paradigm. It's better to understand the problem in terms that do not tie you in to a specific technology. And once you have a clear picture of what need to be built, then choose persistence tech; if that happens to be SQL, you can then translate your solution to SQL.

In my experience, SQL sorely misses sum-types. So I need to find a way to serialize the sum-types of my domain model to SQL.