Re: Transforming 1-1-M Ternary Relationships into Logical

I'm no database expert.. just a student..

I'm using Database Management Systems - Ramakrishnan & Gehrke

To be honest, there isn't an explicit statement.. but the only example for implementing ternary relationships is a create table for the relationship..

My question was whether this is also necessary in the case of a relationship with cardinality of 1-1-M..

Just to put you in the picture.. I identified this ternary relationship in the conceptual model (before finding the cardinalities)....

When I reviewed the relational schema with someone else.. they pointed out.. that my implementation was 2 binary relationships.. and that ternary relationships should always be implemented as a seperate table....however I am finding it hard to accept this..Especially since 2 binary relationships do not capture the concept behind this relationship...

Cimode wrote:
> miklesw_at_gmail.com wrote:
> > What do you mean by "A pointer that allows to design cardinalities"?
> > I'm not following..
> Relationships should not be defined primarily according to the concept
> of cardinality. Definition of relationships is basically defined by
> domain implementation and restriction and numerous other relational
> algebric principles defined by Codd, Date and other knowledgeable
> audiences.
>
> Another way to put it is that you do not seem to be using the term
> *relationship* as it is defined by knowledgeable audiences about
> relational model. But I am curious: which textbook tells you, word for
> word, that *a ternary relationship, meaning 3 attributes are
> necessarily implemented as a FK for all relations* ..Could you provide
> reference?
>
>
> miklesw_at_gmail.com wrote:
> > Most text books state that Ternary relationships are implemented as a
> > table with FKs for all the relations.. i was wondering how are 1-1-M
> > relationships implemented..
> >
> > It seems pointless to me... In 1-M binary relationships.. the FK is
> > placed on the M end...
> > In this case it would make sense to put 2 FKs in the Many end..
> >
> > What is the proper way of implementing this?
> >
> > Tnx,
> >
> > Mike
Received on Wed Oct 04 2006 - 13:32:55 CEST