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"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message <news:bsira5$jlt$1_at_news.netins.net>...
> Marshall agreed with me on something, so I'll dare post one of the many
> questions I have related to relational database theory.
>
> In Date's June 2003 paper entitled "What First Normal Form Really Means" he
> asks questions about MultiValue systems, which he (and no one else I've
> read) abbreviates as "MVS". I am preparing answers to these questions.
> Date writes "...MVS fields are ordered left to right (and so MVS files are
> certainly not relations, and the system is certainly not relational)."
>
> I've been puzzled by this for quite a while, just figuring that relational
> theorists have this wrong. But the writings seem so sure of this. I had
> thought that the relations in relational database theory were mathematical
> relations, but I am beginning to think that might not be the case. My
> masters in mathematics was quite some time ago, so I hauled out some books
> and googled a bit and everything I find that is mathematics, rather than
> database theory, indicates what I thought about relations -- a relation is a
> set of ordered tuples -- right? What am I missing here? An element of a
> relation would be of the form (a1, a2, ... an) where a1 is an element of S1
> etc. They ARE ORDERED LEFT TO RIGHT. Am I misunderstanding something or is
> there some other mathematical definition of "relation" that is the one on
> which relational database theory is based?
A tuple is a set of ordered pairs of the form (attribute, value). Defining an ordering for the attributes would be superfluous.
URL:http://en2.wikipedia.org/wiki/Ordered_pair
You have much to unlearn, Grasshopper.
-- Joe Foster <mailto:jlfoster%40znet.com> On the cans? <http://www.xenu.net/> WARNING: I cannot be held responsible for the above They're coming to because my cats have apparently learned to type. take me away, ha ha!Received on Fri Dec 26 2003 - 21:36:32 CST