Re: I think my book may be wrong about cardinality, but I'm not sure
From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 25 Jul 2007 01:32:43 GMT
Message-ID: <%Kxpi.4401$fJ5.2147_at_pd7urf1no>
>
>
> It means something else. It is the count of relations related
> (with the understanding that a relation could appear more than once
> and thus be counted more than once).
>
> invoice to client: 2-ary
> part number to warehouse to client: 3-ary
>
Date: Wed, 25 Jul 2007 01:32:43 GMT
Message-ID: <%Kxpi.4401$fJ5.2147_at_pd7urf1no>
Gene Wirchenko wrote:
> paul c <toledobythesea_at_oohay.ac> wrote:
>
> [snip]
>
>
>>Just a side question, since I see the term "N-ary relationship" quite >>often. If a relation has N attributes, doesn't it implement (2**N)-1 or >>2**N relationships or thereabouts? Or is that what the term means and >>I've been misunderstanding it all this time?
>
>
> It means something else. It is the count of relations related
> (with the understanding that a relation could appear more than once
> and thus be counted more than once).
>
> invoice to client: 2-ary
> part number to warehouse to client: 3-ary
>
Yes, thanks,
p Received on Wed Jul 25 2007 - 03:32:43 CEST