RE: XQuery

Just a nitpick: SQL WHERE clauses fail with a conversion error if a
conversion fails and the query processor executes a plan that leads to
the execution of the offending conversion.

Actually, the current XQuery rules are pretty close to SQL's rules in
that respect.



> -----Original Message-----
> From: public-qt-comments-request@w3.org [mailto:public-qt-comments-
> request@w3.org] On Behalf Of Bill Keese
> Sent: Thursday, October 16, 2003 7:11 PM
> To: public-qt-comments@w3.org
> Subject: Re: XQuery
> 
> 
> Guido, you suggested that null values be introduced into XQuery, and
met
> with a lot of opposition.  But, from your examples, it seems like what
> you really wanted was something like "use null semantics when
evaluating
> where conditions".  You don't actually want an XQuery expression to
> return null values, do you?  What if where clauses operated like SQL
> where clauses, returning false when there was a type conversion
> exception?  I guess this is pretty much what Michael Kay suggested.
(Of
> course, the counter-argument is that type-exception messages help
> programmers catch errors in their code and their data.   I understand
> both views.)
> 
> >    for $p in document("p.xml")//person
> >    where is_null((number) $p/@age)  /* not exactly XQuery syntax,
sorry
> */
> >    return $p/@name
> 
> You can write this query using the "instance of" operator, right?
> (http://www.w3.org/TR/xquery/#id-instance-of)
> 
> for $p in document("p.xml")//person
> where not($p/@age instance of xs:number)  /* I think this is xquery
syntax
> */
> return $p/@name
> 
> 
>  > Indeterminism sucks!
> By the way, I don't think anyone was really debating your argument
that
> non-deterministic languages have serious disadvantages.  Basically, if
I
> was to paraphrase all the responses, I would say that
"non-deterministic
> languages have many problems, but we can't make XQuery deterministic
> because the performance would be unacceptably bad".
> 
> Bill Keese
> 
> PS: it took me a while to figure out that existentialism has nothing
to
> do with Kafka.  (Especially since every Kafka book's main character is
> named "K", which is pronounced the same as "Kay"...)
>

Received on Thursday, 16 October 2003 22:15:51 UTC