Re: ID field as logical address
Date: Sat, 30 May 2009 11:37:10 GMT
"Bernard Peek" <bap_at_shrdlu.com> wrote in message
> In message <xWQTl.1481$9L2.793_at_nwrddc02.gnilink.net>, Walter Mitty
> <wamitty_at_verizon.net> writes
>>Let's say that the design has followed the practice of including an
>>auto-generated key called ID in every table, and declaring the ID as the
>>PRIMARY KEY. Let's further assume a practice that says that you never
>>update the ID field of any tuple, once it's been assigned. Now let's say
>>you have a table that records values that look like (ID, value). In an
>>actual case, value would probably ityself be a tuple, so our tagged
>>might look like, for example, (ID, LastName, FirstName, PhoneNumber).
>>Now, if we update the LastName, the FirstName, and the Phone number of an
>>entry, it's still the same entry, because the ID field retains the same
> This appears to be an update anomaly but it's not as simple as that. If we
> think of the logical data structure the ID isn't in the same entity as the
> data we want to manage. It's in a separate entity with only one attribute.
> There is supposed to be a 1:1 relationship between the ID entity and the
> data entity, but this is not usually maintained by the database. The
> cardinality of that relationship is managed either programmatically or by
> external business processes.
> Updating the data without making a simultaneous update to the ID field is
> perfectly permissible within the relational model. They are after all in
> separate entities with only a tenuous connection. It's an update anomaly
> and it's caused by failure to fully normalise the data structure.
What would the data structure look like if it were fully normalized? Received on Sat May 30 2009 - 13:37:10 CEST