For one point I do also believe that adding sum types would be great. Even if the only benefit is eliminating 3-value-logic, it is a huge benefit. I also agree

For one point I do also believe that adding sum types would be great. Even if the only benefit is eliminating 3-value-logic, it is a huge benefit. I also agree that while it can be modeled it is very ugly, though I wouldn't necessarily blame the relational model. The relational model is a modelling tool. The physical implementation doesn't need to be 1 to 1 with the model. Same as you rarely find pure OO or pure FP languages. Current DBMSs do also have plenty of solutions for the problem of non-homogenous data. Some allow XML and JSON columns on which you can also enforce schemas. SqlServer proposes sparse tables. PostgreSQL has arrays, enums and structs (and arrays of structs) as data types. But I do agree that sum types ammong other things would really be nice. As for your example I still believe it is incomplete, but I would like to discuss that in a separate thread.