Re: Codd provided appropriate mathematics ... (was Re: Relational and MV (response to "foundations of relational theory"))

"Eric Kaun" <ekaun_at_yahoo.com> wrote in message news:k6r%b.50112$LX2.42031_at_newssvr33.news.prodigy.com...
> As an aside in this discussion, I've seen "multivalued" defined 2
different
> ways in explanations of relational (some of which are really bad).
>
> 1. Where attribute A can hold a list of values (type LIST)
> 2. Where there are attributes A1, A2, A3, A4 (for example), all of the
same
> type and meaning. For example, ADDR1, ADDR2, etc.
>
> Does 1NF refer to both of these? If not, what's the proper terminology for
> each of these cases?

The second is not really a repeating group. It is an ill-advised design choice, but it does not violate 1NF.

A repeating group refers to structure exposed logically regardless whether the structure is a set, list, array etc. The key distinction is whether the logical data model treats the value as something other than a single value with defined operations. Thus the NF^2 models complicate matters by extending the operations on relations to operate on a more complex structure whereas a relational dbms leaves the relational operations as they are and adds domain operations instead. Received on Thu Feb 26 2004 - 20:00:54 CET