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Re: [www-ql] <none>

From: Michael Dyck <MichaelDyck@home.com>
Date: Sun, 04 Mar 2001 11:50:59 -0800
Message-ID: <3AA29CA3.55610586@home.com>
To: www-ql@w3.org
Michael Kifer wrote:
> database languages are designed so that certain queries would be
> expressible *and most queries would not be*. The latter is important so
> that query processors would be able to perform non-trivial optimizations.

Could you give an example of a query that would not be expressible in a
database language?

> An algebra is a procedural language that exists in order to provide
> an intermediate, relatively high language to which you translate a
> declarative language.

So XQuery
    (e.g., FOR $b IN $bib/book WHERE $b/year = 1998 RETURN $b/title)
is declarative, but XML Query Algebra
    (e.g., for b in bib0/book do where b/@year/data() = 1998 do b/title)
is procedural?

I'd say, as far as declarative/procedural "feel" is concerned, they're quite
similar. Specifically, their informal semantics (as given in prose in the
respective WDs) are both phrased in fairly procedural terms (in my opinion,

What is it that makes XQuery declarative but the Algebra procedural?

Received on Sunday, 4 March 2001 14:54:38 UTC

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