From time to time I am toying with idea to extend the classic relational database model - particularly, to be able to define n-ary links between tables - as opposite to the classic model which allows 2-ary links only.

Unfortunatley, like the total majority of projects, this does not go beyound toying with ideas, but sometimes I chat with people about that, and naturally should defend such unorthodox desires.

My almost spontaneous reaction on "Why the hell you may ever want such perverse things as n-ary links?" always was "Hey, dude, look on the real world and you will see n-ary links everywhere!", but then - what a shame - I usually failed to give such immediate examples and mumbled something about customer orders, seasons of the year, and God knows what else nonsense.

But recently I found just a brilliant example from the real world were 3-ary links are just necessary.

Remember Isaac Asimov's novel "The Gods Themselves"? It describes, among all, social, family and sexual life of triads - Parentals, Emotionals and Rationals. One family normally consists of three members of three different genders. So say, we have a table of such creatures and want to describe a relationship "be a memeber of the family". Typical 3-ary link, isn't it? But - alas - if we assume only classic families, which consist exactly of one Parental, one Emotional, and one Rational, this is not such a great example, as it allows relationship between, say, three Parentals, which just can not exist. Or can it? Hey, this is just a homosexual triad family! So we merely should extend our example of triad families to homosexual ones (which probably should be called in this case tri-sexual, but let's stick for the convenience with the old familiar term), and we will get a perfect real-life example of 3-ary links!

It not goes without saying that the very concept of homosexuality among triads is much colorful and interesting than among humans. Humans have only homosexual men and lesbians, and here we have 18 species. And I bet there is subtle psychological differences between, say, Rational which prefers to unite with two Emotionals, and Rational which prefers another Rational and Parental.

But from the other side, while human hetero- and homosexual pairs provide just classic boring 2-ary links, the more involved relationship - those which extends the number of members in the family beyond 2 - provide broader opportunities. So, maybe humans may serve as a good real-life example as well? Hm, but I never encoutered a families of say, three men (or it is just me being not so well informed and updated in that matter?), so yet humans are not perfect example, and it seems I should rely not on human race but on creatures from "The Gods Themselves"...