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Home -> Community -> Usenet -> comp.databases.theory -> Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Paul Vernon wrote:
>Humm. I think I can counter my argument:
>
>TYPE TINY_INT POSREP( {-1,0,1 } );
>
>TYPE TINY_PI
>POSREP( {-1.5 PI, -1 PI, -.5 PI, 0 PI, 0.5 PI, 1 PI, 1.5 PI, 2 PI } );
>
>TYPE TINY_R2 POSREP( { 0 SQRT2, 1 SQRT2 } );
>
>TYPE TINY_POINT
>POSREP POINT_XY (X TINY_INT, Y TINY_INT)
>POSREP POINT_RT (R TINY_R2, T TINY_PI
> CONSTRAINT IF R = 0 SQRT2 THEN T = 0 PI );
>
>Now both poss reps are equivalent, so this is a well constructed type and as
>such not a bad example of a type with more than one possible representation.
>
>:-)
>
>Regards
>Paul Vernon
>Business Intelligence, IBM Global Services
>
>
>
I'm lost on who is countering whose argument here, but you have
described one type that represents the 9 points on and at the
center of the 2 x 2 square at the origin of Z x Z, and another type
that represents 9 points on and at the center of a circle (I think you
may have meant to allow -0.75PI, ..., 0.75PI, 1 PI), instead of twice
these values).
These certainly represent very different subsets of cartesian space, so what do you mean by saying these are equivalent? Once you stray from points of the cartesian form (N,0) and (0,N), I don't think you'll have much luck finding equivalent polar and cartesian representations.
SK
>
>
Received on Wed Feb 26 2003 - 23:46:25 CST