Re: Cardinality - I really need help

"beginner16" <kaja_love160_at_yahoo.com> wrote in message news:1186255408.948471.113990_at_d55g2000hsg.googlegroups.com...
> hello
>
> I would really need some help here
>
> Some time ago I made a thread about cardinality and thought I
> understood it , but today I noticed that I actually misread a post
> explaining cardinality and realized that the subject still very much
> confuses me. Below are the original question and a reply ( the one I
> misread)
>
> >>1)
> >>The following quote ( well I shortened it a bit ) is from a chapter
> >>briefly describing MARTIN E-R notation:
> >>"Say we have entities ORDER and PRODUCT. One ORDER >>must include at
least one product, but it can also have more
> >>than one product. One PRODUCT can be related to zero or
> >>more ORDERS. Thus cardinality of PRODUCT is ( 1, N ) and
> >>cardinality of ORDER is ( 0, N )" But to my understanding, the
> >>cardinality of ORDER entity should be ( 1,N ) --> where 1
> >>means min number of connections and N max number of
> >>connections an individual ORDER entity can have. And
> >>cardinality of PRODUCT entity should be ( 0,N ). But my book claims just
the opposite!
> >>
> > I would have said it differently: the cardinality of the
> > PRODUCT-ORDER relationship with respect to ORDERS is
> > (1,N). the cardinality of the PRODUCT-ORDER relationship
> > with respect to PRODUCTS is (0,N). I think you and I are on
> > the same page, but may need to reread Martin.
>
>
> Cardinality tells a number of connections certain occurrence of entity
> type can have with instances of some other entity type.
>
> a)
> Here is a picture from my book:
>
>
http://s195.photobucket.com/albums/z194/beginner16/?action=view&current=kardinalnost.jpg

The diagram you show in the link is different from the diagarams I am accustomed to.

In the diagrams I am accustomed to, the "(0,1)" would have been placed near the line indicating that the specified cardinality applies to entity E2 in its participation in this particular relationship.

When an entity box participates in multiple relationships, each with its own cardinality, this needs to be kept clear to avoid confusion. Received on Sun Aug 05 2007 - 12:26:49 CEST