Re: more closed-world chatter

Marshall <marshall.spight_at_gmail.com> wrote:

>On May 5, 10:04 am, "David Cressey" <cresse..._at_verizon.net> wrote:
>> "David BL" <davi..._at_iinet.net.au> wrote in message
>>
>> news:1178377225.112732.324630_at_e65g2000hsc.googlegroups.com...
>>
>> > On May 5, 3:16 am, Marshall <marshall.spi..._at_gmail.com> wrote:
>>
>> > [snip]
>>
>> > > def pricedomain = set {1, 2};
>> > > def anotherdomain = set {3};
>>
>> > > def R1 = set(price) [price : pricedomain] {(1)};
>> > > def R2 = set(price) [price : anotherdomain] {(3)};
>>
>> > > def R = R1 & R2;
>> > > ---
>>
>> > > At this point, what is the value of R?
>>
>> > > R = set(price) [price:pricedomain; price:anotherdomain] {};
>>
>> > > Since the union of pricedomain and anotherdomain is empty:
>>
>> > IMO it's confusing to talk about taking a "union of the constraints".
>> > In a sense you are aggregating them. I would call it an ANDing of
>> > constraints as boolean valued expressions, which leads to set
>> > intersections not unions.
>>
>> Sorry to add to the confusion, but I will: the union of the constraints
>> yields the intersection of the data. Clear as mud?
>
>Yes, exactly.
>
>All the constraints that apply in a given context could be thought of
>as a set, or they could be thought of as a single constraint, with
>the terms ANDed together. Furthermore, a single constraint can be put
>in Conjunctive Normal Form and each term can then be separated.
>
>I remember reading about Prolog some years ago, and seeing:
>"the comma can be read as AND" and thinking WTF?! But
>if you have an expression like
>
> x > 0, x < 10
>
>then the comma certainly means AND.

     Not in C.

>http://en.wikipedia.org/wiki/Conjunctive_normal_form

Sincerely,

Gene Wirchenko

Computerese Irregular Verb Conjugation:

     I have preferences.
     You have biases.
     He/She has prejudices.