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Re: newby (very) question on XML DB theory

From: Mikito Harakiri <mikharakiri_at_iahu.com>
Date: Wed, 14 Apr 2004 14:59:09 -0700
Message-ID: <LEifc.42$wb1.48@news.oracle.com>


"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:Eyhfc.71539$0O2.4854903_at_phobos.telenet-ops.be...
> //Courses[starts-with(.//@instructor_last_name, "VAN")]
>
> I've taught this stuff to CS students and non-CS students. I have no
> idea why you think this would be too difficult for the latter. I do,
> however, have an idea why a non-declarative query language that requires
> programming if queries get a little bit more difficult would be
> problematic for them.

May I suggest that XQuery is more complex than SQL? Because it's less pure:-?

Take outer join for, example. As purity is broken (by allowing nulls into result set) selection and outer join operation don't commute anymore. It took me some time (with usenet help) to realize that

select * from t1 left join t2 on t1.id=t2.id and t2.id=2

is different from

select * from t1 left join t2 on t1.id=t2.id where t2.id=2

for example. This is never an issue with ordinary joins and selections. Simplicity of the underlying algebra is the key for the query language success. (Hmm, what about SQL?) Received on Wed Apr 14 2004 - 16:59:09 CDT

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