Re: [External] : Re: Indentation with spaces

[Emanuel Berg]

Drew Adams wrote:

>>   The Closed World Assumption (CWA) is the assumption that
>>   what is not known to be true must be false. The Open
>>   World Assumption (OWA) is the opposite. In other words,
>>   it is the assumption that what is not known to be true is
>>   simply unknown.
>> 
>> Interesting! OWA seems reasonable but how did they come up
>> with CWA, when is that useful
>
> It's simpler to reason with. If you don't know something to
> be true then you conclude that it's false. This is a common
> approach - databases, Prolog etc. Cf. `completing-read' with
> arg REQIUIRE-MATCH = t.
>
> Of course, one can interpret "no match" as just "dunno" or
> "unproven", but often it's acted on as "false". And as Tomas
> perhaps hinted, it's not just about classifying as true,
> false, and dunno.
>
> It's about the difference between any such closed
> classification and a representation or system that's based
> on the idea that both (a) the set of stuff that's classified
> and (b) the classification of that stuff both (1) are
> inherently incomplete and (2) can change.
>
> CWA is akin to not-proven-guilty-means-innocent (or
> not-proven-innocent-means-guilty). OWA assumes only that
> not-proven means not-proven.
>
>> and what's closed about it,
>
> It doesn't allow for the possibility that there are
> unknowns. It assumes that, at any time, what's known to be
> true is all there is.
>
> It's a useful simplification. But it presents difficulties
> wrt the nature of real knowledge and its evolution.
>
>> that you know what you know to be true and every thing else
>> you then and by that can tell is false. So it's a complete
>> state of the knowledge sphere, that's what's closed
>> about it?
>
> Exactly. At any given time. And a system that allows for
> increasing or changing knowledge has somehow to deal with
> non-monotonic changes in what's known (in particular).

I understand, thanks.

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