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

"Bob Badour" <bbadour_at_golden.net> wrote in message news:9OmdndmNiZQA36PdRVn_iw_at_golden.net...
> "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.

But given that types are orthogonal to relations, why is a List type non-relational? Or is it simply in the exposure in the logical model? For example, if I create a LIST type and operations over it, then define a relation with a LIST attribute, and use its operations as I've defined them, is that in some way non-relational or non-1NF?

Would that then apply to any "collection type" (e.g. set, array, etc.), other than relations themselves?

Just trying to identify the boundaries... the discussion of 1NF repeatedly cross the line between relations and types, depending on who's talking. Received on Fri Feb 27 2004 - 21:59:51 CET