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

"paul c" <toledobythesea_at_oohay.ac> wrote in message news:EGupi.4117$rX4.2472_at_pd7urf2no...
> 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?
>
> p

Each tuple in a relation with N attributes corresponds to a point in an N-dimensional space, with each attribute being orthogonal to all of the others. Received on Thu Jul 26 2007 - 03:13:34 CEST