Re: Implementation of boolean types.

Hi,
there was an error in my posting:

> Symbolic programming is a good solution for NULL values....
should be
Symbolic programming is a good solution for UNKNOWN values ...

NULL-a "as a pollution mechanism" are maybe not so bad as a practical solution when expressions with lot's of unknowns get large.

Greeting form Croatia,
Drago Ganic

"Drago Ganic" <drago.ganic_at_in2.hr> wrote in message news:dbdtp6$phk$1_at_sunce.iskon.hr...
> Marshall,
> Symbolic programming is a good solution for null values. See these trivial
> evaluations:
> y = 1+x --> 1+x
> y - x --> 1
>
> z = (1,1,x) --> 2 + x
> z - x -->2
>
> False and x --> False
> True or y --> True
> a = not b --> not b
> c = not a --> b
>
> Remember elementary algebra: We learned how to calculate with unknowns in
> elementary school :-)) But CS forgot to build it in computing. I strongly
> believe CAS [Computer Algebra Systems] are needed for solving the null
> problem.
>
> The practical problem is that expressions with "unknown variables"
> (symbols) tend to get really big
> (e.g. z + y --> (2 + x) + (1+x) -->3 + 2x).
>
> Greeting from Craotia,
> Drago Ganic
>
> "Marshall Spight" <marshall.spight_at_gmail.com> wrote in message
> news:1121534821.846347.260300_at_o13g2000cwo.googlegroups.com...
>> Mikito Harakiri wrote:
>>> Tony Andrews wrote:
>>> > That would be a dumb treatment, really. NULLs propagate in
>>> > computations for numbers, because it makes sense to do so: we really
>>> > don't know what 1+NULL is equal to.
>>>
>>> Not quite: 1+NULL = NULL while sum(1,1,NULL) = 2
>>> No elementary consistency.
>>
>> yeah, that's really weird. the 1+null case shows null
>> having 'unknown' semantics. the sum(1,1,null) case shows
>> null having 'missing value' semantics. So which is it?
>> Clearly, there is no particular consistency.
>>
>> I would prefer a treatment with better consistency.
>> In particular, I see value in using 'missing value'
>> semantics, because how they should behave is quite
>> clear, whereas unknown introduces 3vl which I find
>> unattractive, from the standpoint that it introduces
>> a lot of complexity for little payback. I also think
>> that unknown semantics are better handled by user-defined
>> special values.
>>
>>
>> Marshall
>>
>
>
Received on Sun Jul 17 2005 - 17:54:23 CEST