Re: [Qexo-general] Interface between XQuery-Engine and XML-DB

[Per Bothner]

Maik Thiele wrote:
> > It's quite possible.  I'd write a class in Java that acts as an
> > XQuery function whose result is the filtered output.  Your class
> > would emit calls to the Consumer that Qexo provides.
>
> Sounds good. But can you describe it with a little example please.
> It's quite difficult for me to understand the oodles of code.
> Is there point in the parsing procedure of Qexo where xpath expressions
> were picked out explicit so I can work with them?

I don't think you'r question makes sense.  Remember that XQuery
is a superset of XPath, so "picking out xpath expressions"
doesn't happen.  Xpath expressions can be mixed in with
other expressons in all kinds of convoluted ways, and there
is no shipping of xpath expressions to a separate xpath engine.
If the Qexo implementation of xpath expressions is defective,
then we need to improve Qexo.

What I meant was that if you have some expression that takes
an input XML dataset, and then applies an xpath transformation
on that to filter the data, before doing some more complex
non-xpath computation, then you might write some Java code
that pre-filters the dataset using some external xpath engine
before passing the filtered data as input to Qexo.  Especially
if the external xpath engine can make use of indexes or whatever
to improve speed.

> I don't
> understand want you mean with the class which emit calls to
> the Consumer.

My idea is that the combined action of reading some xml and
applying an xpath filter can be viewed as a special-purpose
"intelligent" xml parser or an "xml producer".  In Qexo an
xml producer can generate xml-style data by invoking
the methods of a Consumer object that it is passed in.
--
        --Per Bothner
address@hidden   http://per.bothner.com/