Re: Multiple-Attribute Keys and 1NF


"JOG" <jog@xxxxxxxxxxxxx> wrote in message
news:1188303981.637381.32500@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I am still fighting with the theoretical underpinning for 1NF. As
such, any comments would be greatfully accepted. The reason for my
concern is that there /seems/ instances where 1NF is insufficient.

Insufficient for what? I wasn't able to infer this from your example.

An
example occurred to me while I was wiring up a dimmer switch (at the
behest of mrs. JOG, to whom there may only be obeyance). Now I don't
know the situation in the US, but in the UK a while back the colour
codes for domestic main circuit wiring changed. Naturally the two
schemes exist in tandem, as exhibited in every house I've had the joy
of doing some DIY in:

Brown -> live.
Red -> live
Blue -> neutral.
Black -> neutral.
Green and yellow -> earth.


In the US, house current is typically at a nominal 120V, except for a few
circuits, like stoves that are driven at a nominal 240V. Nominal 120V can
vary all the way down to 110V. At some point below that, "brown out"
begins.

Where the coded meaning of the wires gets to be "interesting" is where you
have an overhead light controlled by a wall switch. If there are two double
pole switches controlling the same light it gets more interesting.

In general, the meaning is:

Black -- live
Red -- live (out of phase with black)
White -- neutral
Green -- ground
bare -- ground.


However, in many homes, the wire from the appliance to the controlling
switch has been
The stove in my house has a clock/timer on it that is driven by 120V is
wired with the standard 3 connector wire consisting of a white wire, a black
wire, and a bare wire.

In this case, the black wire is used to carry (unswitched) power from the
overhead junction box to the switch. The companion white wire is used to
carry (switched) power from the switch to the power side of the light
circuit, which is a black wire.

The above results in a white wire being connected to a black wire. This
looks "wrong" to a DIY neophyte. The official code uses bits of colored
tape to indicate such things as "white coded as black", but that's over my
head.

The electrical wiring in some homes dates back about a century, before the
wires had colors. Things get really interesting then.

All of this is a digression from 1NF. Again, 1NF is insufficient for
what?



.

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