Re: DBDesign Q

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 Mon Nov 24 2003 - 22:58:55 CET