Re: Sets and Lists, again

On 23 May 2006 10:12:40 -0700, "Marshall" <marshall.spight_at_gmail.com> wrote:

>Gene Wirchenko wrote:
>> On 22 May 2006 17:49:21 -0700, "dawn" <dawnwolthuis_at_gmail.com> wrote:
>> >>
>> >> Indexes are physical, not logical.
>> >
>> >No. I am using the term as an index of an array. Array[n] where n is
>> >the index. If there is a list in a DBMS named emailAddresses, then the
>> >3rd element of that array is (logically) emailAddresses[2] (or [3],
>> >depending on the implementation of Arrays) and '2' (or '3') is the
>> >value of the index for that element.
>>
>> Since you are discussing implementation, it is physical.
>
>"Index" has more than one meaning. Yes, "index" in the context
>of CREATE INDEX is physical, but that is not what is being
>discussed here.

     Nor are we discussing book indexes. Your point is irrelevant.

>If you have, say, a list of email addresses to send a notification
>to, with the order determining which ones to try, in order,
>until successful delivery, then the order is part of the logical
>model. The fact that this list can be physically represented
>as an ArrayList or a LinkedList without affecting the logical
>model makes it even more apparent that the order here
>is logical.

     In short: The order is logical. The index is physical.

     Now, reread what I wrote. I said the second part. I understood the first part implicitly.

Sincerely,

Gene Wirchenko Received on Tue May 23 2006 - 19:24:43 CEST