# Re: All hail Neo!

Date: Sun, 23 Apr 2006 13:58:14 GMT
Message-ID: <WJL2g.64598\$VV4.1223196_at_ursa-nb00s0.nbnet.nb.ca>

Frank Hamersley wrote:

```>> Frank Hamersley wrote:
>>
```

>
> [..]
>
```>>>> In that line of thought, here's an interesting question that Date et
>>>> al have posed before to the n-VL folks:
>>>>
>>>> If "exists but empty" is true and "doesn't exist" is false, what is
>>>> null?
>>>
>>> Neither and both!
>>
>> I find that sort of handwaving to be a complete non-answer.
```

>
> I suspect you are wearing the darkly tinted glasses of preconception.
> Whilst I was trying to show a little wit, the current 3VL state of
> affairs still seems to me to fit that description.
>
```>> A much more intellectually honest reply would be: "I don't know."
```

>
> Not from this black duck (on this occasion)!
>
```>> or "Null has no similar analog in set theory."
```

>
> I wasn't comparing/contrasting the RM with set theory. Perhaps for you
> it is implicit?

No, it is quite explicit. Relations are sets. Relational algebra is the equivalent of set theory, and relational calculus is the equivalent of predicate calculus.

```>> True and 1 both have the exact same analog in set theory. False and 0
```

>
> Perhaps but insistence on a parallel form for the RM does not seem to
```>> This has a certain elegance and symmetry.
```

>
> I agree that and readily subscribe to that in my own endeavours.
>
```>> In canonical form:
>>
>> {} = 0 = false
>> {{}} = 1 = true
>>
>> What is the similar analog for null?
```

>
> My prior knowledge of your/the notation is non existent but I can prolly
> deduce its intent. So having a stab at it how about ...
>
> {}{} = null

> As an aside (and with no malice aforethought) I am curious why the 0 and
> 1 figure at all? Forced to conform I would probably go with ...
>
> {}{} = -1 = null