Re: DBDesign Q

Too bad you're not.

"Bob Badour" <bbadour_at_golden.net> wrote in message news:0vOdnX5rxah44l-iRVn-iQ_at_golden.net...
> Alan,
>
> Very briefly, you are an ignoramus. Multiple foreign key references among
> relations and cyclical references among relations are perfectly normal and
> acceptable.
>
> "Alan" <alan_at_erols.com> wrote in message
> news:bpttkf$1rvv8s$1_at_ID-114862.news.uni-berlin.de...
> > Very briefly. An ERD models business entities and relationships, and
there
> > can be > 1 relationship between the same enities. When you map the ERD
to
> a
> > realtional schema these multiple relationships combine into
non-redundant
> > tables.
> >
> >
> > "Bob Badour" <bbadour_at_golden.net> wrote in message
> > news:rtGdnVlFq_Dx1l-iRVn-ig_at_golden.net...
> > > "Alan" <alan_at_erols.com> wrote in message
> > > news:bpthmj$1t348d$1_at_ID-114862.news.uni-berlin.de...
> > > > It is correct on an ERD, but incorrect in a relational schema.
> > >
> > > That's a rather astounding statement. How do you propose to support
your
> > > assertion?
> > >
> > >
> > > > "Andy" <net__space_at_hotmail.com> wrote in message
> > > > news:edb90340.0311232036.e0eeae5_at_posting.google.com...
> > > > > Can two entities have more than one relationship between them?
> > > > >
> > > > > A(A_ID PK,..., bID FK)
> > > > >
> > > > > B(B_ID PK,..., aID FK)
> > > > >
> > > > > A.bID refers to B.B_ID
> > > > > B.aID refers to A_ID
> > > > >
> > > > > 2. Does it make sense?
> > > > >
> > > > > Product (ProductID PK, Name,., SpecialAttrID FK)
> > > > >
> > > > > Attribute (AttrID PK, Name,..,ProductID FK)
> > > > >
> > > > > Product can have many attributes. One attribute belongs to only
one
> > > > product.
> > > > > There is only one main("special") attribute for each product
> > > > >
> > > > > Thank you in advance,
> > > > > Andy
> > > >
> > > >
> > >
> > >
> >
> >
> >
>
>
Received on Tue Nov 25 2003 - 21:43:43 CET