[xquery-talk] Linking Saxon through to exist database

[Michael Kay]

> 
> I've installed exist and using it's sandbox its working fine.
> 
> Can I connect a query to that database and use Saxon for the 
> query engine?
> 

Only if you want to treat eXist as a simple substitute for a filestore
containing XML documents that can be retrieved by name/URI. You can do that,
but the performance is going to be very similar to what you get when the
documents are actually in filestore - or possibly worse.

You're not going to see Saxon decomposing your query (or XPath expression)
and shipping parts of it to eXist to take advantage of eXist's indexes, or
to retrieve only the parts of the documents that your expression actually
needs. That's not because it's technically infeasible, but because it's a
pretty sophisticated piece of technology that would cost a lot to develop
and test and would be priced correspondingly.

The DataDirect XQuery engine does this kind of query decomposition to access
data from multiple data sources, but as far as I know it currently accesses
only relational back-end databases and XML in filestore, not XML databases.
I'm sure the technology is quite capable of accessing an XML data source,
but the cost of integrating each supported data source is likely to be high.

Michael Kay
http://www.saxonica.com/