xml-dev - Re: XML-QL

[Joe Lapp <jlapp@webMethods.com>]

At 05:53 AM 9/2/98 -0700, Don Park wrote:
>No.  XSL is definitely not a query language although it uses ideas which
>could be useful for querying.

I would argue that XSL patterns is definitely a query language, but that
the template language portion of XSL (the big picture) probably is not.

>[...]
>When we are talking about XML query language, are we talking about
>expressing a query in XML or are we talking about an expression, not
>necessarily in XML, that will return information from data sources, not
>necessarily XML document repositories, in XML format?

I can represent SQL in XML, OQL in XML, even XPointers in XML.  XML is a
way to represent data structures.  I can represent C, C++, Java, and Pascal
all in XML if I want to.  I can chose an XML representation that provides
exactly the information found in the non-XML representation.

This suggests to me that the more interesting challenge is to create a
language that queries data structures that are represented in XML, not to
just create a query language that is expressed in XML.

I don't mean to make any statement about whether this language for querying
XML should itself be expressed in XML -- that's an orthogonal issue.

>[...]
>BTW, there is another topic related to XML-QL which is XBE or
>XML-[query]-By-Example.  I am not sure if anyone is working on it because I
>just thought of it <g>.  You just write an example of the XML document you
>want by specifying the tags as you want it and fill in the values to match.
>XBE engine uses it to return the data the way you want exactly, rejecting
>mismatches and weeding out unwanted information.

Interesting approach -- sort of the inverse of XSL -- but I suspect that in
order to be useful it won't be so simple.  In its simplest form, you'd only
return the elements that you provided, serving only as an existence test,
returning no other information.  QBE at a minimum requires wildcards, and
it would be interesting to find an appropriate set of wildcards.
--
Joe Lapp, Senior Engineer | jlapp@webMethods.com
webMethods, Inc.          | Voice: 703-267-1726
http://www.webMethods.com |   Fax: 703-352-0370

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