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

Hi Bob,

The assignment text was misleading as it spoke of "breeding" and "conception".. I think thats were I screwed up.

I might have figured out where 1-1-M can/should be 2 binarys;

When a "Child" or entity on M end has total participation..the mother and father FKs are not nullable.. the relationship between mother and father is "secure"..

However, if the entity on the M end has partial participation..you can't be sure both entities on the 1 end participate in the relationship

Tnx,

Mike

Bob Badour wrote:
> miklesw_at_gmail.com wrote:
> > 1-1-M = Ternary Relationship (A,B,C)
> >
> > A can have 1 B and 1 C
>
> Thus A has two foreign key references: 1 to B and 1 to C.
>
>
> > B can have Many As and Cs
> > C can have Many As and Bs
>
> The question then becomes: Other than a shared A reference, which is
> already captured by the two foreign key references to B and C above, how
> are B and C related?
>
>
> > http://groups.google.com.mt/group/comp.databases.theory/tree/browse_frm/thread/33c2956edca34a75/0e88b26bd53dcb2c?rnum=1&hl=en&_done=%2Fgroup%2Fcomp.databases.theory%2Fbrowse_frm%2Fthread%2F33c2956edca34a75%2F0e88b26bd53dcb2c%3Fhl%3Den%26#doc_b95911d131acf57a
>
> Are you talking about A=child, B=mother, C=father? In this case, A has
> two binary relationships: the maternal relationship and the paternal
> relationship.
>
>
> > Bob Badour wrote:
> >
> >>miklesw_at_gmail.com wrote:
> >>
> >>>What do you mean by "A pointer that allows to design cardinalities"?
> >>>I'm not following..
> >>>
> >>>Cimode wrote:
> >>>
> >>>
> >>>>You are using an incorrect terminology. You believe a relationship is
> >>>>a pointer that allows to design cardinalities (it is not). The proper
> >>>>way for you to deal with the problem you are describing is to do some
> >>>>serious reading about relational model...Here is the reference...Hope
> >>>>this helps...
> >>>>
> >>>>Introduction to Database Theory by CJ DATE
> >>>>
> >>>>
> >>>>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
> >>
> >>Hi Mike,
> >>
> >>Cimode is a crank. In general, you can safely ignore him; however, his
> >>pointer to Chris Date is sound.
> >>
> >>I suspect the reason you have not received any better responses is
> >>nobody really has any idea what you are talking about.
> >>
> >>If you have any 1-1 relative cardinality between two relations, you can
> >>reduce that into a single relation, which would seem to leave you with a
> >>simple 1-M foreign key reference. However, I am not confident that I
> >>even know what you mean by 1-1-M.
> >
> >
Received on Wed Oct 04 2006 - 19:52:19 CEST