Re: Antw: Re: Sobre las querys en XML

[Vivien Malerba <malerba gears linuxave net>]

On Fri, Oct 20, 2000 at 10:04:16AM +0200, rodrigo linuxave net wrote:
> > First some Citations:
> > 'XQL is a notation for retrieving information from a document'
> > and :
> > 'The XQL Proposal, a superset of the XSL pattern syntax, addresses the
> > information retrieval aspects of queries.'
> > and:
> > 'An important area commonly associated with query languages is
> > database management functions including operations such as
> > create, delete, update, insert. This area is not currently addressed
> > by either XML-QL or by  XSL.'
> >
> 
> ok, so for the moment, it's not database-oriented but document-oriented?
> 
> >
> > Conclusion:
> > XQL is some (powerfull) kind of (SQL-) select, that allows to extract data
> > from within a arbitrary complex DOM-tree, but:
> > - It doesn't support joins
> > - AFAIK it doesn't support grouping
> > - it has only one aggregate method count(), that AFAIK does something like
> >      'SELECTCOUNT(*) FROM table WHERE condition'
> >
> > So I think XQL is no substitute for XmlQuery
> >
> > Of course there is a non-empty intersection of XQL and XmlQuery:
> >
> > If the XmlQuery happens to be a select, that extracts some data from
> > a single table, it could by replaced by the correnponding XQL equivalent,
> > because each table could be identified with a simple structured XML document.
> >
> > IMO this small intersection does justify a total redesign of XmlQuery.
> 
> well Gerhard, you and Vivien are the people who had put their work on the
> XML queries, so I think a redesign of XmlQuery is ok only (and only if) there is
> something useful to be added to what you've done. So, if you think XML queries are
> more powerful than this XQL stuff, let's continue like this, and if in the future
> we find that XQL are useful we can:
> * add support to XML queries for XQL
> * add XQL as an option "query language" to the report engine (that is, it will
> support SQL, XML Queries and XQL)
> 
> or we could do what Derek says: create our own free standard (just dreaming?)
> 
> cheers
> 

I also think that it is better to continue with the XML queries. The XQL is
however an attempt to make queries expressed in a universal way. It is quite
incomplete, and not really suited to our needs. We can also have a look
at a specification which is the latest from the W3C regarding XML Query.

at http://www.w3.org/XML/Query there are some interresting things.
also at http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html there
is a library which AFAIK implements the XML Query as proposed by the W3C.
I don't know what its license is though!

As I said I think we should keep with our XML queries model (and thanks to
Gerhard we will soon have something to test), and keep an eye on the W3C
XML Query. IF then the XML Query is adopted and IF we need some features
which are difficult to do with our XML queries THEN we may think about moving
to the W3C XML Queries. This is my point of view.

There is no point at changing now for no good reason.

Cheers,

Vivien