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Re: Fwd: [bdbxml] xquery puzzle

From: Michael Dyck <jmdyck@ibiblio.org>
Date: Sat, 10 Dec 2005 15:43:01 -0800
Message-ID: <439B6805.BE58227@ibiblio.org>
To: www-ql@w3.org

"L.G. Meredith" wrote:
> 
> Michael,
> 
> Thanks for taking a whack at it. But, there was a slight
> misunderstanding. The predicates hold of a (sub)collection -- not of
> an element.

Ah, right. Well, that should be even easier:

  function decompose( input-set ):
    element coll {
       for bipartition in bipartitions( input-set, (), () )
       where p1(bipartition/coll[0]) and p2(bipartition/coll[1])
       return bipartition
    }

  function bipartitions( remaining-input, part1_so_far, part2_so_far ):
    if remaining-input is empty:
       element coll {
         element coll {part1_so_far},
         element coll {part2_so_far}
       }
    else
      let h := head(remaining-input),
          t := tail(remaining-input)
      return
      (
        bipartitions( t, part1_so_far + h, part2_so_far )
        ,
        bipartitions( t, part1_so_far, part2_so_far + h )
      )

Or, you could push the "p1 and p2" test into bipartitions(); it would
make the latter un-generic, but it might save space, depending on
the XQuery implementation.

-Michael

  
    

>        function decompose( input-set ):
>          element coll { foo( input-set, (), () ) }
> 
  function foo( remaining-input, p1s_so_far, p2s_so_far ):
>          if remaining-input is empty:
>             element coll {
>               element coll {p1s_so_far},
>               element coll {p2s_so_far}
>             }
>          else
>            let h := head(remaining-input), t :=
>      tail(remaining-input)
>            return
>              if p1(h): foo( t, p1s_so_far + h, p2s_so_far ) else:
>      ()
>              ,
>              if p2(h): foo( t, p1s_so_far, p2s_so_far + h ) else:
>      ()
> 
>      It should be fairly straightforward to translate that to
>      proper XQuery.
> 
>      -Michael
> 
> --
> L.G. Meredith
> 
> 505 N 72nd St
> Seattle, WA 98103
> 
> +1 206.650.3740
Received on Saturday, 10 December 2005 23:43:21 UTC

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