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   Re: XML query language

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  • From: Paul Janssens <paul.janssens@skynet.be>
  • To: xml-dev@ic.ac.uk
  • Date: Tue, 30 Mar 1999 16:27:36 +0200

Oren Ben-Kiki wrote:
> Paul Janssens <paul.janssens@skynet.be> wrote:
> >I think (iii)
> (results should be XML)
> >should not be a requirement of an XML query language. The
> >result of a query  could be a vector of tuples of pointers to the
> >individual matches. Whatever needs to be done with that output can be
> >done in a layer above that.
> I fail to see the benfit in inventing a new format for query results. First,
> a set of tuples with pointers, or whatever else, can be easily expressed in

No problem there, my point was that ONLY this information should be the
output of a query, preferably in an XML format :-)

> Second, if one wants to obtain 'pointers to the output', then it should
> be a simple matter of constructing in the result a pointer to the matched
> tree (<A href="..."> or something) instead of the matched tree itself.
> AFAIK all XML QL proposals produce XML as output.
> >Just because SQL mixes content with style
> >doesn't mean an XML query language should.
> You lost me here; this is the first time I've heard that SQL has anything to
> do with style. The result of an SQL query is a table and is typically
> accessed via some programming API which has nothing to do with presentation.
> I agree that an XML query should do the same thing - that is, create an XML
> tree as a result without worrying about presentation. The fact that I think
> that _the transformational part_ of XSL should do this is perfectly
> consistent, since I see this part as being a general independent mechanism
> and not just a "style" language.

Ok, sql ALLOWS you to mix style (or semantics) with content, as in

SELECT '<A href='||col1||'>'||col2||'</A>' FROM table1

For the same reason, if an xml query language allows you to arbitrarily
construct result trees, lazy users will abuse that feature to put style
or semantics in the output so they will not have to postprocess it with

If on the other hand, only pointers to the resulting matches are
returned by the query language, anyone that wants an output is FORCED to
use XSL.

In my opinion, an xml query language should only describe a set of
equations, an xml query language implementation should only solve these
equations, and whatever is done with the result is NO business of the
query language.

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