Re: MV Keys (was: Key attributes with list values)

From: Marshall Spight <marshall.spight_at_gmail.com>
Date: 26 Feb 2006 16:46:43 -0800
Message-ID: <1141001203.183508.309920_at_i40g2000cwc.googlegroups.com>


Bob Hairgrove wrote:

>

> It's not quite that simple. As David pointed out, a "mushroom and
> onion pizza" is not necessarily different than an "onion and mushroom
> pizza". But the ordering of the bits in an integer is significant,
> whereas the ordering of ingredients for a pizza isn't (although I'd
> definitely want to make the crust before I put the tomato sauce on
> it<g>).

For sure. An int is a list of bits, unless what you want to do is use an int to represent numbers in the range 0 - 32. :-)

> One of the fundamental things in RM is that the Cartesian join of two
> relations is commutative. Think about the implications of this when
> trying to decide what requirements a MV key would have to fulfill.

I thought about it a bit and it seems to me the issue raised is one of equality testing. To do an equijoin, one has to be able to determine equality. So if one was joining on a relation valued attribute, one needs to be able to decide whethe two relation values are equal. Which means the system has to be clear that {a, b} == {b, a}, which is certainly an issue.

Is there anything else you had in mind?

Marshall Received on Mon Feb 27 2006 - 01:46:43 CET

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