Re: boolean datatype ... wtf?

From: David BL <davidbl_at_iinet.net.au>
Date: Thu, 30 Sep 2010 07:27:08 -0700 (PDT)
Message-ID: <4048f43d-331f-4a70-82bc-1b647919a7c7_at_x18g2000pro.googlegroups.com>



On Sep 30, 9:41 pm, David BL <davi..._at_iinet.net.au> wrote:

> Example : I have the means to measure (x,y) in a cave but not z. I
> want to record pH measurements taken on every stalagmite or
> stalactite. Relation is
>
> pHLevels(x,y, isStalagmite,pH)
>
> isStalagmite is part of the key.

My example is no good. Obviously it is easy to eliminate the 2-valued attribute in this case by introducing two relations

	Stalagmites(x,y,pH)
	Stalactites(x,y,pH)

One can always remove a 2-valued attribute by using a pair of relvars (irrespective of whether it is part of the key). If this is done repeatedly the number of relvars grows exponentially.

In my example of recording a relation with 4 boolean attributes, one could in fact introduce 16 relvars that each have an empty heading and hold DEE or DUM.

So a "compelling example" would need a key involving perhaps 5 or more 2-valued attributes in the key such that splitting into many relvars is awkward.

Tricky... Received on Thu Sep 30 2010 - 09:27:08 CDT

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