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Re: Fw: XML query language

  • From: Paul Prescod <paul@p...>
  • To: XML List <xml-dev@i...>
  • Date: Wed, 31 Mar 1999 11:48:59 -0600

Re: Fw: XML query language
Oren Ben-Kiki wrote:
> 
> >You don't need an element. You just need a nodelist. Look at the DOM's
> >brutally named "getElementsByTagName" method.
> 
> You mean the NodeList contains the matched nodes directly, and not XPointers
> which point to them. 

Right. Pointers to, not copies of, the nodes. And the pointers should be
in the most efficient "syntax" allowed by the system. In a Python program
it is a PyObject reference. In C++ it is a DOMNode *. In a
process-portable XML encoding it is an XPointer. Everybody is focused on
this last case but it is only a special case.

> >If you are asking me what is the syntax for a nodelist then I'll say it
> >has no syntax. It is an abstraction like the record set returned by a
> >database. If you have to move the query result between machines then you
> >can choose an encoding (quite likely XML) but that's outside of the realm
> >of the query language itself -- it is akin to report writing.
> 
> No standard way to represent a query result as text? I find this strange.

I didn't say that there should be no standard way. I said that the
standard way is not something that the query language should specify. If
there are 6 query languages (some standardized and some proprietary) and 6
result encoding syntaxes (some standardized and some proprietary) then you
should be able to use any query language with any encoding syntax.

> Both XML-QL and XQL have ways to construct results (CONSTRUCT and
> <xql:result>). 

There is no such element type described in
http://www.w3.org/TandS/QL/QL98/pp/xql.html

> OK, if what you are saying is:
> 
> - We have two languages:
>   (i) matching of XML elements, which we'll call XQL for the moment, and is
> basically the XSL match pattern language;
>   (ii) constructing XML trees from other XML trees which we'll call XTL for
> the moment and is basically the <xsl:*> tags.
> - XSL is the combination of both (plus FO objects).
> - XQL is usable in other contexts then XTL.
> - There's no other standard XML construction syntax other then XTL.
> 
> Then we agree. 

Yes!

> I'd also add:
> 
> - We should have separate specs for XQL, XTL, and FOs. The XTL spec should
> simply reference the XQL spec. The FO spec should be independent.

Techically a good idea but I think that it is politically impossible to
separate XSL and its matching language at this point. Maybe XSL 2.0 will
depend on whatever XML QL is eventually standardized.

> - XQL should be used wherever a set of XML elements needs to be selected
> from an XML tree.
> - So therefore CSS should allow using XQL in its selectors. For that matter,
> CSS should allow an XML syntax :-)
> - And also XPointers?

I agree with all of this but changes to CSS are unlikely in the
short->medium term.

-- 
 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself
 http://itrc.uwaterloo.ca/~papresco

"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
http://www.wired.com/news/news/culture/story/10124.html

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