Re: PostgreSQL and XML support

On Tue, 06 Sep 2005 18:48:01 +0400, Andrey Fomichev wrote:

> Hello!
>
> I would like to raise a discussion about XML support in PostgreSQL. I'm a
> person who is quite experienced in XML data management and new to
> PostgreSQL. So, excuse me if I ask trivial questions about PostgreSQL...
>
> I tried to find something about support for XML in PostrgreSQL. As far as
> I understand, PosgreSQL does not have native support for XML. But I've
> found several works around.
> 1. XML databases build on top of PostgreSQL. They are XpSQL and XDB
> (sorry,
>    if I missed something). Are they alive and functionable?
> 2. Contribution made by John Gray (xml and xml2). This is a tool that uses
>    'shredding' for storing XML in relational tables (another words, it
>    decomposes XML document into nodes and places these nodes into tables
>    in such a way that we can reconstruct this document back). What do you
>    think about this tool?
>

Actually, it doesn't do anything to the document - it just treats it as a
text string (I believe XpSQL, for example, decomposes a document into
constituent parts). The xml2 contrib module is concerned with providing
convenient functions to use XPath queries against such documents. I'd love
to do better indexing of them, and have looked at GiST, but I haven't got
the understanding needed to accomplish that!

> In general, I have the following questions to PostgreSQL users. - Are
> there any of you who need to store and query XML data? - Do you already
> use PostgreSQL to store XML data or you are
>   just thinking about it?
> - If you store XML data in PostgreSQL, how do you do it? What tool
>   do you use?
> - Do you need some advanced query capabilities? Like XQuery, XPath 2.0 -
> Do you need some advanced update capabilities? Like node-level updates
>
>
> And I have the following question to PostgreSQL developers. Do you have
> any plans for native support for XML in PostgreSQL? By native support I
> understand persistent data structured specially developed for storing XML
> on disk and query/update it efficiently. As far as I know, native
> support for XML is a way other database vendors (Oracle, Microsoft, IBM)
> go.

I think there's quite a bit of "buzzword" usage going on from database
vendors - it depends on what your use case is what sort of approach you
want to take. The advantage of decomposing documents is that you can more
readily access the structure of them, but recomposing them is slower.
Storing documents as text strings has the advantage that they are easily
retrieved (and verified against digital signatures, which may be important
for some applications) but are more difficult to represent as a DOM
(though how that fits with a relational model at all is the question!)

Updates would be interesting - but quite a large project, I suspect.

I hope that helps. I am a developer more than a user and I can't speak for
people's usage. Others may well do that.

Regards

John