Re: Natural keys vs Aritficial Keys
Date: Thu, 28 May 2009 11:56:46 GMT
Message-ID: <2_uTl.1221$9L2.373_at_nwrddc02.gnilink.net>
"David BL" <davidbl_at_iinet.net.au> wrote in message
news:f20bd044-adea-41d5-b301-9dd0f57ed736_at_z16g2000prd.googlegroups.com...
> The ORM idea makes the blunder because it assumes incorrectly that the
> values within a set can be identified independently of their value.
> ORM wants to make this assumption so that a variable that records a
> set of values can instead be interpreted as a set of variables.
>
The last several exchanges in this thread have gone over my head. Oddly enough, this last paragraph brings the discussion full circle, back to where I started.
Consider a set of tuples. Or maybe a set of current states of tuple-variables. (That's the part that's over my head.) Now consider a set of simple identifiers, called ID. ID could have values like 1,2,3,... or any other sequence that can be auto generated and guarantees identity. (The word "sequence" rather than the word "set" is intentional here.) Now merge ID with the original set of tuples, by arranging the set in an some arbitrary sequence. now associate the first tuple with the first ID, the second tuple with the second ID, etc. etc. until every tuple in the set has been identified with an ID. Call this the tagged set of tuples.
Now what you have is a set of tuples where the ORM assumption makes sense, after a fashion. The values in the original set can now be identified independently of their value, because each of them has been tagged with this artificial key called ID, one that can be used for identification purposes.