ORMs aren't implemented in the database, so it's less of an "inner" and more of a "parallel" platform. I think this is an important distinction, since one of th

ORMs aren't implemented in the database, so it's less of an "inner" and more of a "parallel" platform. I think this is an important distinction, since one of the reasons people use ORMs in the first place is better integration with the programming language of their choice. Moreover, there are often practical reason to re-implement those features you've mentioned. Let's take constraints as an example. Can you use them to display a list of user-friendly validation messages when someone fills out a web form? Will they benefit from all the tools (version control, refactoring, static verification) your language of choice provides? How reusable will they be? If there were databases with language-friendly APIs for these things, I bet developers would be less likely to re-implement them.