Antw: Re: Sobre las querys en XML

["Gerhard Dieringer" <DieringG eba-haus de>]

>>> <rodrigo linuxave net> 19.10.2000  12.39 Uhr >>>
> Hi all!

> This is a message from Josemi, a friend of mine who I've been trying to get
> into gnome-db programming for the last year, and he now seems to be getting
> into it with this by proposing the following:
>
> why, instead of inventing the XML queries, don't we use XQL, which is an
> established standard and is being adopted by many database servers?
>
> I myself don't know much about XQL, so I don't know if this is a good idea or
> not. Please comment on it.
>
>cheers
>
> > Una preguntilla, mas que currarse desde cero algo para hacer querys en XML,
> > pq no utilizais un estandar como XQL, que lo van a soportar las bases de
> > datos ???
> >
> > http://www.w3.org/TandS/QL/QL98/pp/query-transform.html 
> >
> >A lo mejor es una burrada lo que he dicho, en ese caso sorry, else guay
> >
> > Salu2

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.'

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.

------------
Gerhard