Re: I think my book may be wrong about cardinality, but I'm not sure

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 24 Jul 2007 19:12:27 -0300
Message-ID: <46a6791f$0$8850$9a566e8b@news.aliant.net>

paul c wrote:

> David Portas wrote:
>

>> "beginner16" <kaja_love160_at_yahoo.com> wrote in message 
>> news:1185301676.680771.29780_at_b79g2000hse.googlegroups.com...
>>
>>
>>> 2)
>>> Relationship between two entities is called binary connection or
>>> second degree relationship. But connection can exists between more
>>> than just two entities. Level of connection is determined by the
>>> number of different entity types that exist in a connection.
>>>
>>> Now as far as relational DB goes, don't tables have only binary
>>> connections ( second degree relationship )?
>>>
>>
>>
>> No. An N-degree table implements an N-ary relationship between 
>> attributes - attributes which may well identify other entities. Do not 
>> assume relationship = foreign key. A foreign key is just one type of 
>> constraint (not necessarily the only one) for enforcing referential 
>> integrity in RM.
>>

>
> 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?

They each describe a single relationship of a particular arity. Received on Tue Jul 24 2007 - 17:12:27 CDT