Re: boolean datatype ... wtf?

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 - 16:27:08 CEST