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At 12:52 PM -0700 5/7/02, Jonathan Robie wrote:
>One use case is the Use Case R, which is currently too complex
>precisely because it lacks a schema, which forces us to use casts to
>get some things to come out right. Here are some examples:
>
>1.4.4.2 Q2 - as is:
>
><result>
> {
> for $i in document("items.xml")//item_tuple
> let $b := document("bids.xml")//bid_tuple[itemno = $i/itemno]
> where contains($i/description, "Bicycle")
> return
> <item_tuple>
> { $i/itemno }
> { $i/description }
> <high_bid>{ max(for $z in $b/bid return decimal($z)) }</high_bid>
> </item_tuple>
> sortby(itemno)
> }
></result>
>
>Without the cast, max() would sort according to the string value,
>not the decimal value.
I would propose more simply that max() and similar functions always
treat their arguments as numbers. I personally have never heard of a
max() function that operates on strings anyway. Even if you tried to
define it as the last in sort-order or some such, it really depends
on the sort order, so you need an additional argument, not that this
is a natural thing to do in the first place.
I suppose you might have a more logical max on date and time types,
but again it's not common. I propose instead a latest() and
earliest() which would always treat their arguments as dates. This
seems much more natural to me than either of the solutions you
propose.
Similarly, the avg() function should convert all nodes passed to it
to numbers, as if by the XPath 1.0 number() function.
>You can pick through the whole Use Case R and see many examples like
>this. Every single cast is superfluous in these use cases, present
>only because there is no schema.
>
I skimmed them. Nothing jumped out at me that couldn't be handled by
my proposal, but maybe I missed something. In brief, I suggest if you
pass something to a function that expects a number, it's converted to
a number. If you pass something to a function that expects a date,
it's converted to a date. No muss, no fuss. What am I missing?
>There are two reasons I don't like these casts. One is that it is
>tedious. The other is that when I cast, I tell the static type
>system that I think I'm smarter than it is, and it will simply
>believe me that $z is a decimal. If I'm wrong, this may result in an
>error which I will not encounter until run time.
>
Casting presumes types. If we eliminate static typing from the
language casting is no longer needed, just like in XSLT 1.0 where all
the conversions are automatic.
--
+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
+-----------------------+------------------------+-------------------+
| The XML Bible, 2nd Edition (Hungry Minds, 2001) |
| http://www.cafeconleche.org/books/bible2/ |
| http://www.amazon.com/exec/obidos/ISBN=0764547607/cafeaulaitA/ |
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