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 Tue Aug 15 2006 - 18:55:09 CDT
