On 3/8/2011 5:34 PM, Darren New wrote:
> Is it the same telephone pole if I dig it up and plant it somewhere
> else? Sure, maybe. But am I ever going to need to know that if my job
> involves routing cables? Probably not. Am I going to need to know that
> if my job involves replacing them when they wear out? Most definitely.
>
> How often do you replace the little tags on the side of the pole that
> give the pole number? Not very often. Is there any reason if that ID tag
> gets replaced that you can't just update in the database everyplace that
> appears? Probably not.
>

Poles move all of the time, but they are considered 'new' poles and not 
related to the old poles :-)  pole tags usually do not change, but if 
the tag is missing on one day, it could have a new one the next.  In 
fact, the power companies here tag their poles according to geographical 
coordinates - likely they use it as their primary key.  But I have seen 
some wrong tags that will likely get changed.

>> But sure, especially if you're recording historical data (which is of
>> course especially unlikely to change), there's no real need for a
>> synthetic key.
>
> I contend that most primary data in the database should be historical.
>
>> Until the GPS coordinates turn out to have been inaccurate.
>
> Then you fix it. There never *was* an intersection with those GPS
> coordinates. So you fix it. The point is to avoid collisions, not to
> necessarily have a PK that never changes.
>
> Given that the BIGGEST TRANSACTIONAL DATABASE IN THE WORLD (*)
> identifies street intersections with GPS coordinates, I'm gonna have to
> go with GPS coordinates on this one. ;-)
>
>
> Assuming those don't change, they're probably based on geometry also.
> The point of using GPS coordinates is that they are guaranteed not to
> change. If you enter them in the database wrong, then you have bad data,
> but that's not because the intersection moved.
>

I will stay out of this one....  I think I will stick with auto number 
fields for now - just to keep my head on straight.

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