Re: XQuery support

Andrew Dunstan wrote:
>
>
> Matthias Brantner wrote:
>>>> I know this has been discussed several times and it seems the
>>>> conclusin was it's impossible if we would like to use existing XQuery
>>>> external modules (some are by license reasons and some are by
>>>> techinical reasons).
>>>>
>>>> So it seems the only way to support XQuery is, developing our own
>>>> XQuery functionality from scratch. I'm wondering if other people reach
>>>> the same conclusion as me, or is it a totaly impossible project?
>>>>
>>
>>
>>> Well xquilla on top of xerces should get us pretty much were we need
>>> to go. They are both under the Apache 2 license, which I believe
>>> would be ok. But they are C++ so I don't know if we could use them.
>>> I found Zorba, its C++ and Apache 2. But I don't know much about it.
>>> But it looks promising.
>>> http://www.zorba-xquery.com/
>>>
>> Sounds like a great project. Please, let us know
>> (zorba-users(at)lists(dot)sourceforge(dot)net) if you need any help or have
>> questions with regard to plugging Zorba to PostGreSQL. We would love
>> to see this happen and help.
>>
>>
>>
>
> Well, maybe you can answer the questions I had last time I looked at it,
> namely:
>
>> XQuery is a whole other question. Adding another library dependency is
>> something we try to avoid. Zorba <http://www.zorba-xquery.com/> might
>> work, but it appears to have its own impressive list of dependencies
>> (why does it require both libxml2 and xerces-c? That looks a bit
>> redundant.)
>>
>> Even if we did implement XMLTABLE, I think I'd probably be inclined to
>> start by limiting it to plain XPath, without the FLWOR stuff. I think
>> that would satisfy the vast majority of needs, although you might feel
>> differently. (Do a Google for XMLTABLE - every example I found uses
>> plain XPath expressions.)
>
> A much more urgent need we have, IMNSHO, than for XQuery, is for XSLT
> support that actually works. But maybe that's just me.

I've been playing around with Zorba and xQilla today. I couldn't
actually get Zorba to build on my system. It looks like the two share a
common (or similar) C API though. Zorba also had perl, Python, Ruby and
PHP bindings (which I also couldn't get to work) but would be nice to be
able to use from plperl, plpython, plruby also.

If it were possible to drop the xerces dependency from Zorba and use
libxml2 for parsing, that would be a strong case for it. The other big
dependency for Zorba was ICU for converting character sets. I'm not
familiar with that part of Postgres. But it seems to me that we would
have our own libraries for that sort of thing.

I'm not a big fan of doing XSLT in the database. But xQilla would give
you XSLT 2.0 support.

Scott