Re: A real world example

Ultimately I think it's comes to this:

• If you need to compare an entity over time, you must pick a key that will allow consistent identification over time (a surrogate if necessary).
• If there is _nothing_ that is consistent over time, then the entites you thought were the same thing, are not.
• If a key value must be changed for some reason, but it is only the "label" that is changing (e.g. if two companies surrogates must be merged, the new surrogates are still subsitutes for the exact same distinguishing attributes as they were before), then this also must be done retroactively to old relation values to maintain inter-rv integrity.

As an example to illustrate the last point, consider if the company was taken over by a french corporation, who demanded the database be translated to french. This necessarily requires changing old relation values too if one wants to make comparisons, and thats certainly no flaw in relational theory. Received on Wed Aug 16 2006 - 01:55:09 CEST