Re: If you were to implement the original relation algebra language...

"Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message news:<bpkvlo$1h6a$1_at_gazette.almaden.ibm.com>...

> > a*b+c = (a*b)+c
> >
>
> I guess we would be better off moving away from infix operators and using
> prefix/functional operations instead in relational algebra grammers.

It is unimportant IMO.

> "I have added prefix JOIN and prefix UNION here, to allow more than two
> operands in each case.
>
> Tutorial D as currently defined has only infix versions of these operators.
> UNION ( a, b, c ) is
>
> equivalent to ( a UNION b ) UNION c, not that it matters where you put the
> parentheses, of
>
> course. Similarly, JOIN ( a, b, c ) is equivalent to ( a JOIN b ) JOIN c,
> and again it doesn't matter
>
> where you put the parens."

According to TTM ( a UNION b ) UNION c is also equivalent to a UNION b UNION c

But it does not work (like other things) with the Tutorial D grammar we can find in Hugh's page.

But of course a UNION b UNION c should be converted to a single UNION during the expression normalization process.

Regards
  Alfredo Received on Sat Nov 22 2003 - 19:23:39 CET