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   Re: Fw: XML query language

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  • From: Paul Prescod <paul@prescod.net>
  • To: XML List <xml-dev@ic.ac.uk>
  • Date: Tue, 30 Mar 1999 09:48:30 -0600

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. 

It isn't about a format. Query languages do not typically work on formats.
They have an input data model (i.e. a relational data base) and they have
an output model (i.e. a set of records). An XML Query Language should also
work in terms of the XML data model (the information set).

> First,
> a set of tuples with pointers, or whatever else, can be easily expressed in
> XML. 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.

The IDL for an XML QL should be something like:

NodeList XMLQuery( DOC doc, String query )

Your alternative is:

String XMLQuery( String inputdoc, String query )
DOM XMLQuery( DOM inputdoc, String query )

That's just forcing the query engine to do more work -- much of it
unnecessary in most cases.

Let's put it this way: you are saying that the query engine should build a
list of pointers, build a tree, generate XPointer attributes just so that
an application can get back the original list of pointers!

If the application wants to turn the list of pointers into a tree, it can
do so. That's what XSL does.

> AFAIK all XML QL proposals produce XML as output.

No, XQL goes out of its way to NOT require that the output be XML. "The
specification does not indicate the output format. The result of a query
could be a node, a list of nodes, an XML document, an array, or some other
structure. That is, XQL does not dictate the binary format of the returns,
but rather the logical returns." The same is true of XSL patterns.

 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself

"Perpetually obsolescing and thus losing all data and programs every 10
years (the current pattern) is no way to run an information economy or
a civilization." - Stewart Brand, founder of the Whole Earth Catalog

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