Re: Recursive join - blind alley?

interesting articles...
but I don't understand the math in the first article he says

   function child_numer
   ( num integer, den integer, child integer )    RETURN integer IS
   BEGIN
      RETURN num*power(2, child)+3-power(2, child);    END;    function child_denom
   ( num integer, den integer, child integer )    RETURN integer IS
   BEGIN
      RETURN den*power(2, child);
   END;    select child_numer(3,2,3) || '/' ||

          child_denom(3,2,3) from dual

   19/16

but I get, using an evaluation order [power] -> [*/] -> [+-]

   num*power(2, child)+3-power(2, child)    3*power(2,3)+3-power(2,3)
   3*9+3-9
   27+3-9
   21

and

   den*power(2, child)
   2*power(2, 3)
   2*9
   18

so it should be 21/18 or my math wrong ?

"Mike MacSween" <mike.macsween.nospam_at_btinternet.com> wrote in message news:<3ff9ff22$0$52882$5a6aecb4_at_news.aaisp.net.uk>...
> "Mike Sherrill" <MSherrillnonono_at_compuserve.com> wrote in message
> news:3gtjvvk4t71etrf73iddsjqsb6qgu5fufi_at_4ax.com...
> > On Fri, 2 Jan 2004 08:53:47 -0000, "Mike MacSween"
> > <mike.macsween.nospam_at_btinternet.com> wrote:
> >
> > >This will be an orchestral management system. Musicians and other staff
> > >being booked/paid for jobs.
> > >
> > >A job may contain other jobs, e.g:
> > >
> > >World Tour contains
> > >US leg and Europe leg (and others)
> > >US leg contains State tours (and others)
> > >New Jersey tour contains Hoboken concert (and others)
> > >Hoboken concert contains dress rehearsal, 1st show, 2nd show
> >
> > I'd just observe that a world tour is probably a tour, not a job.
> > Whatever a job is. A tour isn't a leg. A leg isn't a job.
>
> As you aren't sure what a job is then I don't know how you can state that a
> world tour isn't one.
>
> It's perfectly clear what a job is. It's the name I've applied to an entity
> type. An instance of which may be related to other instances of the same
> entity type. This looks like the sort of thing that could be modelled using
> some sort of hierachical structure. You seem to have other ideas. Perhaps
> you could let me know what they are.
>
> > >Or a job may be single:
> > >
> > >My band plays at Simon Foreman's barmitzvah
> > >
> > >To account for the variability I imagined a recursive join.
> >
> > What else did you imagine?
>
> What does that mean? I imagined what I said I imagined. A recursive join.
>
> Since then I've found out about materialised paths and nested sets. Nested
> intervals look useful:
>
> http://dbazine.com/tropashko5.shtml
>
> But I'm afraid my maths isn't up to understanding it fully.
>
> Yours, Mike MacSween
Received on Tue Jan 06 2004 - 13:45:47 CET