> > The point is that I would have expected that problem to be solved > > within the past four decades since relational databases have been > > invented. Or at least in the past two decades since PostgreSQL has > > been developed. > > Then what about n>1, n>2, n>k where k an arbitrarily large positive > integer? isn't it the same problem class actually?
Not quite. In conceptual modeling, relationships between entities aren't directed. And there's no reason to not have a "not null" constraint on any of the two sides of a one-to-many (or many-to-many) relationship from the conceptual point of view. The way relationships are implemented in physical database schemas, by foreign key constraints, just makes it non-trivial to implement such a "not null" constraint on the "wrong" end of a one-to-many relationship. But this a technical issue with the implementation of databases at the physical level, not a conceptual issue. > Is there any serious database vendor who provides out of the box > support for 1:n, n>0 ? Or is it an "unusual" user requirement in the > first place. It definitely is not, since conceptual diagrams I have seen are full of such relationships. They're just never correctly implemented at the physical level. > Ever thought why not so many people have asked for this? Having quite some professional experience in companies, I don't doubt for a second that the very only reason is simply total absence of care for scientific correctness of database at the level of the physical implementation. Sincerely, Wolfgang -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
