Examples for one-to-one associations?

can anyone give me some *real-world* examples for one-to-one associations (in contrast to one-to-one aggregations and compositions) in the relational model/SQL? The examples I saw so far were just too unrealistic.

An example for one-to-one aggregations might be a database for a car repair shop: car - engine is one-to-one and engines might be assigned to other cars (or none at all).

In the context of a scrapping company, which doesn't re/move parts, but needs to track important parts because of a law, the car-engine relationship could be considered composition (the engine is part of the car and is removed from the DB when the car is scrapped).

But are there any real one-to-one, loosely coupled associations?

If so, who references who in a relationship between two equivalently positioned/leveled entities?

Karsten Received on Sat Jun 05 2010 - 12:33:24 CEST