Hello,

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

Examples of one to ones:

1) Spouse

2) Health Policies (for Employees' Company-Sponsored Plan)

hoodwill wrote:
So say you but what people want to record is what decides what
'associations' are reflected by a db. Since the atom was split it has
been questionable whether any such associations could be innate. Some
people want to believe a person has one soul, others think some people
have no soul and they will never agree on a common context unless they
agree to take souls out of discussion which may be a first step toward
mastering abstraction. It may be natural but it's a mistake, also
impractical, to yearn for a reality that reflects technology. Context
of a db overrules such willfulness and mysticism, those must be put
aside when using a db (admittedly this rarely happens which must be part
of the reason why there is so much confusion and abuse of mechanical
systems and why personal nuances, spiritual or otherwise are usually
out-of-scope). In the relational world, what some call 'business
rules', others call constraints and others call predicates are the only
reliable source of such context, even though some experts will persist
in saying for example that zero has special meaning compared to other
numbers at the same time as they insist on including it in a number domain.


It's really a waste of time to argue about associations. It might be
more profitable to examine the motives for the popularization of the
association concept so many years ago, which I think involved nothing
more important than searching for machine analogies that made
implementation obvious, not necessarily perfect capture of human wishes.

On 6/5/2010 8:49 PM, hoodwill wrote:

Sorry, I know, not very sensitive, but I couldn't resist. I love Bill
Paxton in Big Love.


--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>

"It's really a waste of time to argue about associations."

Why are you then?

hoodwill wrote:
Hardly arguing. I don't argue with newage nuts I know either, just try
to keep them away from me, point them towards their own kind. Just
doing my little bit to help keep this group (and myself) from wasting
time. According to my newsreader, nobody had wasted any time here from
May 31 until this came up on June 5. Maybe somebody who follows more
groups can suggest a soft fuzzy one that might be more receptive to this
stuff, maybe there is a db recipe group. I'm all in favour of such
groups if they keep such topics out of here.

On Jun 5, 12:33*pm, Karsten Wutzke <kwut... (AT) web (DOT) de> wrote:
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.

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.

A one-to-one relationship exists equally between both. Why do you
want to allocate ownership of the relationship to either entity?

On Sat, 5 Jun 2010 20:49:59 -0700 (PDT), hoodwill
<chase.saunders (AT) gmail (DOT) com> wrote:

You need a time element. Even given monogamy, many people have
been married more than once.

Sincerely,

Gene Wirchenko

Gene Wirchenko wrote:

Even more basic than that: Some folks are single.

On Mon, 07 Jun 2010 15:25:07 -0300, Bob Badour
<bbadour (AT) pei (DOT) sympatico.ca> wrote:

Like me.

"Forest, meet tree. Tree, forest."

I was thinking of optional myself, but should have said
something.

Sincerely,

Gene Wirchenko