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From "Scherler, Thorsten" <thors...@apache.org>
Subject Re: XML-Query language
Date Mon, 01 Dec 2003 21:21:50 GMT
Marc Portier wrote:

> nope, not that I know of
> 
I thought so looking into the examples.


> 
> hm, you are looking at XMLQuery as a way to query around in some kind of 
> document-database.  This will only be performant if there are some 
> indexes pre-created for the available documents targetted for the 
> queries you are going to launch...

The website I mentioned before is doing it with the help of of a DTD. 
That way the parser "knows" where to look. I think the authors where not 
refering on a db but on "normal" xml-Files. I find that aproache quit 
nice :).
> 
> Hence you live more or less in the assumption of an XMLDatabase which is 
> more or less the natural habitat for XMLQuery implementations
> 
> (although there is a group of people that like the syntax more then XSLT 
> and would welcome the FLOWR expressions for single file transformations 
> as well. Haven't seen it happen however)
> 
The XPath approach of Xindice for 
example(http://xml.apache.org/xindice/guide-user.html#Querying+the+Database) 
has big disadvantages. Consider something like 
http://javaboutique.internet.com/tutorials/Murachs/index-2.html where 
you can put a SQL-String to search a db (I speak of "total" freedom of 
the Query-String). I didn't get something similar working with XPath.  e.g.:
with (where *expr* is a parameter parsed from a formular):
expr=date[date='Nov 28']
...
<xsl:param name="expr" />
...
<xsl:apply-templates select="{$expr}"/>
This is not working, neither *select="$expr"*, nor *select="'{$expr}'"* 
(or I did something wrong). I came to the conclusion that you can't use 
dynamic XPath expression.

Or do you?

> 
> What sizes are we talking about? For really small sets you might 
> consider aggregating all into one file and using plain XSLT (probably a 
> fair amount of xsl:key usage)

Ok, we talking about log-Files from Mail, FTP, HTTP,... So there will 
become quite big.

> 
> But again, this has the sound of pre-indexing all over it.  Depending on 
> the variety of queries you need to service you could consider making 
> these index files yourself or switch to some XMLDatabase. (or even a 
> bread-and-buther RDBMS)

But that will make it necessary to know the index (key) to make a query. 
That is not really user-friendly.
> 
> This would mean that you process the separate XML files when they are 
> being stored. (e.g. to put parts of the info they hold into the RDBMS)
> 
> regards,
> -marc=
Thanks for your reply Marc, maybe you have some comments ;-)

King regards
</thorsten>



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