Re: Examples for one-to-one associations?

On Jun 5, 12:33 pm, Karsten Wutzke <kwut..._at_web.de> wrote:
> can anyone give me some *real-world* examples for one-to-one
> associations

Sometimes, corporations/agencies/governments require exclusive associations - a employee may not hold multiple positions or occupations, a professor may not chair more than one department, etc. In addition, in resource allocation problems, associations between resources at any particular time often excludes others of the same kind - we may only assign one parking space (or one driver) to one vehicle at a time, a teacher can only teach one subject to one class in one room, and so on.

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

Your own examples with cars and engines illustrate that association, aggregation and composition conflate the relation with a mereological interpretation. The recent threads on IS-A and HAS-A in this group contain my own struggles with them. Instead, unique constraints and referential constraints on relations can express logical requirements precisely and sufficiently.

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

A one-to-one relationship exists equally between both. Why do you want to allocate ownership of the relationship to either entity? Received on Mon Jun 07 2010 - 20:05:44 CEST