Re: set-valued values
From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 08 Dec 2006 01:10:11 GMT
Message-ID: <TX2eh.439310$1T2.321088_at_pd7urf2no>
>> Another maybe crazy question - if instead of 'atomic values' (whatever
>> that means) a relational engine (note for David, I've avoided using
>> the term 'DBMS' !) expressed only values made up of sets, would the
>> presence of the empty set in both true and false extensions create any
>> problems? (I'm thinking that the relational requirement of attribute
>> names means there is no problem, eg., the presence of empty sets is
>> just an artifact of the mechanism that can usually be safely ignored.)
>>
>> As for representation, sometimes such values can't be represented
>> without access to other 'attributes', eg., values that are internal to
>> an engine. My attitude (no reasoning involved I'm afraid to say) is
>> that it's okay to give the builtin result 'true' in such cases. That
>> way, the engine can proceed to manipulate the expression if further
>> requests of made of it, concerning that result.
>>
>> p
Date: Fri, 08 Dec 2006 01:10:11 GMT
Message-ID: <TX2eh.439310$1T2.321088_at_pd7urf2no>
Bob Badour wrote:
> paul c wrote: >
>> Another maybe crazy question - if instead of 'atomic values' (whatever
>> that means) a relational engine (note for David, I've avoided using
>> the term 'DBMS' !) expressed only values made up of sets, would the
>> presence of the empty set in both true and false extensions create any
>> problems? (I'm thinking that the relational requirement of attribute
>> names means there is no problem, eg., the presence of empty sets is
>> just an artifact of the mechanism that can usually be safely ignored.)
>>
>> As for representation, sometimes such values can't be represented
>> without access to other 'attributes', eg., values that are internal to
>> an engine. My attitude (no reasoning involved I'm afraid to say) is
>> that it's okay to give the builtin result 'true' in such cases. That
>> way, the engine can proceed to manipulate the expression if further
>> requests of made of it, concerning that result.
>>
>> p
>
>
> I don't see why the value would appear in both sets. An empty set is
> different from a set containing the empty set as it's only element.
>
> {} != {{}}
It's a conundrum for me. On one hand, if the empty set is contained in one extension, de Morgan tells us it is not in the other. On the other hand, its lack of an attribute seems to make it a member of both sets.
p Received on Fri Dec 08 2006 - 02:10:11 CET