null is often used in relational databases to be semantically equivalent to "info missing". I get that this use of null isn't ideal. However there are quite a

null is often used in relational databases to be semantically equivalent to "info missing". I get that this use of null isn't ideal. However there are quite a lot of cases where it is semantically equivalent to "not applicable"; while some of these cases can be avoided with a restructure, some can't, and in either case I don't see a compelling argument to do so. e.g. a parent_id column that is null for top-level objects in a hierarchy. Restructuring the database to avoid this seems like moving to an unintuitive paradigm in pursuit of rule-following for its own sake.