Re: Database design pattern question

In article <1121628648.995189.91800@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, --CELKO-- <jcelko212@xxxxxxxxxxxxx> writes 
This design fallacy is called attribute splitting.  You are putting
things that belong to one entity split over multiple tables.


I'm afraid I don't understand this point.

Temporal things are stored with a (start, end) timestamp pair.  They
have durations and are not points in time.  You can get the details at
University of Arizona's website -- look up Rick Snodgrass and download
his book.


The book looks very interesting. Thank you.

I suppose it might help if I explain a bit more about my application. Some of the data comes from different sources, with different levels of reliability. So for instance my event tables might store information about the source of the data as well as the time stamp and the data itself. I can also imagine wanting queries which use data from the most reliable source rather than the most recent.

A better example attribute might be surveying a person's favourite colour at different times. Really all you have is a snapshot in time. There isn't really an interval of validity resulting from the survey. Although once I have read Snodgrass I might get a feel for whether it is helpful to use an interval for which the information is most current.

The disadvantage of this approach would be that I could no longer simply merge multiple copies of the database by forming unions of the event tables.

I should really emphasise that the ability to update multiple copies of the database then merge them is the key issue I am trying to solve. Keeping a transaction log may be a better solution than what I was proposing, but I have a prejudice against having the same information recorded in multiple places.

--
Andrew McLean
.

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