# Re: Extending my question. Was: The relational model and relational

From: Bernard Peek <bap_at_shrdlu.com>
Date: Sun, 23 Feb 2003 23:02:27 +0000
Message-ID: <POmBX4LDMVW+Ewgf_at_diamond9.demon.co.uk>

>"Bernard Peek" <bap_at_shrdlu.com> wrote in message
>news:Mg9p99xYCBW+EwiW_at_diamond9.demon.co.uk...
>> In message <7Ik5a.164\$8e.17186852_at_mantis.golden.net>, Bob Badour
>>
>> >> You and Date insist that cardinality can only be determined by
>counting,
>> >> which
>> >> requires distinguishability. I have a scale that allows me to
>determine
>> >> the cardinality
>> >> of a multiset of tuna cans by their collective weight.
>> >
>> >If you cannot identify the cans of tuna, how do you place them on the
>scale?
>>
>> You pick one of them up (any one will do) and put it on the scale.
>
>Exactly! And by picking one you have identified it.

Nope. You have one can but its presence in your hand is not an intrinsic property of the can and so does not identify it. The can you hold and any of the others could be exchanged without affecting any of the data in the system.

>
>
>>You
>> don't need to identify which can you are choosing (given the assumption
>> that all of the cans have the same weight).
>
>Ah, but the very action of picking one can up identifies the can. It becomes
>the can in my hand and then the can on the scale. It becomes identified as
>separate and different from all other cans.

>
>If the cans were not identifiable, you would not be able to knowingly pick
>one or to knowingly grasp one.

>
>
>> >And before you can calculate a count from a weight, you must first count
>> >identifiable cans then weigh them.
>>
>> No, you have to count cans. You do not have to count identifiable cans.
>
>How do you know whether you are weighing cans if you cannot identify any?

>For the time the cans are on the scale, they are identifiable and are
>distinguishable from all other cans both on and off the scale.

If you take some cans from the multiset and place some of them on the scale you have split one multiset into two multisets. If you drop all of the cans into a bag after you have finsished weighing some of them, how do you pick out the cans you claim to have identified?

>
>If you cannot identify cans, how do you know which cans you have already
>counted and which cans remain to count?

At no point do you need to identify any specific cans. You can place the cans you have weighed into one pile and the ones you haven't into another. What this does is to create a new attribute that didn't exist before you sorted the cans. You could just as easily take a sharpie and write a Can Number on each one.

```--
Bernard Peek
bap_at_shrdlu.com
www.diversebooks.com: SF & Computing book reviews and more.....

In search of cognoscenti
```
Received on Mon Feb 24 2003 - 00:02:27 CET

Original text of this message