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Re: MERGE as the imperative form of aggregation

From: paul c <toledobythesea_at_oohay.ac>
Date: Mon, 16 Apr 2007 04:10:06 GMT
Message-ID: <yGCUh.82245$aG1.56433@pd7urf3no>


Brian Selzer wrote:
...
> Update may be "ugly," but it's a necessary and primative operation. It is
> not just a combination of insert and delete. Because a key value can only
> be used to identify a tuple in single database state, update provides the
> means to correlate the tuples in the preceding state with those in the
> succeeding state so that transition constraints can be enforced.
...

Whenever I've heard people say that update is not a combination of delete and update, without exception they've failed to describe it using any kind of fundamental algebra or calculus. Once, I even heard it described as the equivalent of replacing the upper metal on a traffic stop sign, the notion being that the post holding up the sign stayed intact.

That is why I continue to think that UPDATE is a creation of a dbms's environment and no more than that. Nothing wrong with such convenient devices, but they are not fundamental. Any equivalence that is present resembles low-level assembler macros, not the model itself.

INSERT is clearly the rm's set union and DELETE a conjunction of a negation.

p Received on Sun Apr 15 2007 - 23:10:06 CDT

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