Re: More on identifiers

From: Walter Mitty <>
Date: Fri, 05 Jun 2009 14:05:08 GMT
Message-ID: <oC9Wl.801$>

<> wrote in message On Jun 5, 1:25 pm, "Walter Mitty" <> wrote:

>> Consider two electrons. They both have the same mass, and they have the
>> same charge. They might have opposite spins. But the minute we add a
>> third
>> electron, the spin of two of them is going to be identical. It seems
>> that,
>> on the surface at least, electrons do not have enough properties to carry
>> identity.

>If objects are really not distinguishable then why someone would want
>to artificially identify them? Wouldnít be better to record just their

Good point. So there are some case where identity is not important.

(Incidentally, the other response where the comment was made that two electrons must occupy different states leads to a slippery slope. Using state to identify implies that a change of state is in effect a change of identity. This is related to Brian's claim that all attributes of an entity are mutable. (Am I misinterpreting your claim, Brian?)

A case where identity seems unimportant to the requirements is products bearing UPC codes on supermarket shelves. The UPC identifies the product as a member of a class of interchangeable things on the shelf. It doesn't matter which one you take to the chckout counter, they are all going to ring up the same, for both pricing purposes and inventory control purposes. There might be a unique identifier somewhere on the product, but it's not obvious.

Supermarket sales slips are a notorious example of a situation where what is presented on the slip is not a set of things bought, but a list of things bought. In a list, each item can be identified by its position. Thus two items with the same content but different position will not be treated as "the same item included twice." Confusion between sets, lists, and bags is responsible for a large number of bugs. Received on Fri Jun 05 2009 - 16:05:08 CEST

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