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abnormal forms

From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 12 Apr 2006 17:22:56 GMT
Message-ID: <QHa%f.6021$WI1.5342@pd7tw2no>


JOG wrote:
> Change bothers me. Especially in database schema, and specifically when
> we want to accomodate change in the cardinalities of the relationships
> we are modelling. ...

(I made a new subject because I didn't have anything particular to say about the original multiplicity question except that it refreshed questions about rva's that have been troubling me for a couple of months.)

My questions are equally fuzzy, but I'll post them in case somebody can make a comment that gives me a better angle than the ones I've thought of so far.

First, I have a presumption that two relations can express the same value in different ways, ie., via different descriptions or expressions.

    For example, most people are familiar with the axiomatic attitude that different writings of attribute/column order don't change anything material.

The first question is, is there anything axiomatic about an sva (single-valued attributes) relation when compared to an rva relation that has the same attributes?

For example, (using ttm-style braces and for convenience omitting type names), is a SUPP{S#} relation logically the same value as a SUPP{{S#}} relation that is (somehow) constrained to have only one tuple? (not to be confused with one that somehow allows multiple tuples).

pc Received on Wed Apr 12 2006 - 12:22:56 CDT

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