Re: What is a Relationship !?

>I feel like most of the papers I have read about E-R seem to be avoiding
>really dealing with the questions in particular relationships
>what to they mean a relationship is the association of entities ???
>
>Is a relationship the fact that they are related e.g. book on a shelf
>meaning that the place of a book is on the shelf
>i.e. something that he is like the height of a man ???
>
>Or is a relationship something by itself that is the relationship
>e.g. component in recipe meaning a physical something that is
>the same as the component and is in the recipe ???

The RM does not make a distinction between the two.

My understanding is that the E-R diagrams were introduced (in the 70's) to make things easier, because it was assumed that people would have a hard time digesting the facts that relationships (the N:M ones anyway) are entities.

By making this artificial distinction it actually makes things *harder* to understand. And it could sometimes contribute to the fact that modellers failed to realise that these "relationships" could have relationships with other "relationships" resulting in bad models.

Just another example of an originally simple concept (entity) being muddled.

Ted Codd divides entities (I think in the RT/M-paper) into kernel entities, associative entities and characteristic entities. This is a useful framework but it is really just a framework.

best regards,
Lauri Pietarinen Received on Thu Nov 20 2003 - 14:05:55 CET