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

On 26 juil, 03:13, "Bruce C. Baker" <b..._at_undisclosedlocation.net> wrote:
> "paul c" <toledobythe..._at_oohay.ac> wrote in message
>
> news:EGupi.4117$rX4.2472_at_pd7urf2no...
>
>
>
> > David Portas wrote:
> >> "beginner16" <kaja_love..._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.
What does that mean ? How is a single attribute orthogonal to N-1 attributes part of the same relation?. What do you exactly designate as *orthogonality*? Why would a tuple necessarily be a point and not a line ofr plane in geometrical N-space? What about degree 0/1 relations? How does a degree 0 relation represent a point in space? Received on Thu Jul 26 2007 - 12:39:47 CEST