Re: The Practical Benefits of the Relational Model
Date: Tue, 1 Oct 2002 11:42:52 +0200
Message-ID: <3d996e20$0$52166$edfadb0f_at_dspool01.news.tele.dk>
"John Jacob" <jingleheimerschmitt_at_hotmail.com> skrev i en meddelelse
news:72f08f6c.0209301959.41f55690_at_posting.google.com...
> We welcome criticism of the product and of the theory on which it is
> based as long as that criticism is well founded. This was the reason
> for my retort to Mikito. We actively search for solutions.
Well, this answer is far more precise than Nathans!
> I firmly believe we must maintain some degree of
> precision in these discussions. Sorry if I used D4 syntax, but I feel
> it is fairly clear, perhaps even more so than SQL because it
> explicitly outlines the operations taking place.
I will accept that answer. For my part, I do believe that I understand D4 syntax.
> While I must admit that the statement does sound like a bullet from a
> data sheet, it is in no way a vacuous remark. Perhaps we could
> rephrase it thus: all the operators of the relational algebra have
> well-defined semantics regarding updatability. These semantics work in
> concert with each other to effect updatability no matter what
> operators are involved in a given expression, just as the retrieval
> operations have a specific affect, so the update operations have a
> specific effect, meaning that there is a kind of updatability closure
> over the operators of the relational algebra. Therefore, for any
> combination of relational operators used to define a given view,
> including ones involving scalar expressions such as extend, we can
> determine the effect of an update against that view. One of those
> effects is obviously an error.
Kind regards
Peter Koch Larsen
Received on Tue Oct 01 2002 - 11:42:52 CEST