Re: Multiple-Attribute Keys and 1NF

From: David Cressey <>
Date: Tue, 28 Aug 2007 13:35:59 GMT
Message-ID: <3xVAi.147$_A5.50_at_trndny03>

"JOG" <> wrote in message
> 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? Received on Tue Aug 28 2007 - 15:35:59 CEST

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