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Date: Mon, 10 Apr 2006 16:03:51 -0400
To: objectiveviewdiscussion@googlegroups.com
From: "Scott W. Ambler" <s...@ambysoft.com>
Subject: ovdiscussion Re: Relations, Relationships
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At 02:53 PM 4/9/2006, Remco wrote:

>(i am also not e database expert)I meant probably  relationship. But I
>do not see a logical difference everything that connects elements of
>sets  is a relation in the mathematical  sense. I recognize the
>terminology you are describing and i agree but the relationship of the
>ER model you can always implement as a table as you can model any
>relationship/relation as tuples in math. But what is the kind of
>unidirectional relationship in the real world Scott revert to ??

Restricting the conversation to the real world, and not to 
mathematical and/or relational theory, here are some examples of 
uni-directional associations:

1. Management maintains a private list of people of their "up and 
coming stars", but those people don't know that they are on the list
2. A person drew someone else's name from a hat and must now buy them 
a "Secret Santa" gift.  The buyer knows who the receiver is, but the 
receiver doesn't know who is giving them the gift.
3. A CIA agent is assigned to monitor five suspected foreign agents, 
but these people do not know they are being monitored.

In all three cases one entity has knowledge of another entity, but 
not vice versa, making them uni-directional associations.  You can 
read about uni-directional associations in the UML literature 
published by the OMG if you want to find out more about them.

At 03:15 PM 4/9/2006, Remco wrote:

>I meant to say somthing like by joining and projection and ... you can
>create other valid relations/relationships  in your model if you define
>them explicitly or not . (again i am not a database expert and not a
>native English speaker but I Am not stupid as Scott seems to think)

I never said that you were stupid, although other people who have 
posted messages on this list have unfortunately used that terminology.

- Scott

====================================================
Scott W. Ambler  :-)
Senior Consultant, Ambysoft Inc.
www.ambysoft.com/scottAmbler.html

Refactoring Databases: Evolutionary Database Design 
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