It is basically a way to store XML in it's native format (i.e.
hierarchically) within DB2 instead of having to "translate" it into
relational format in order to store it. This means you don't have to
parse the XML on its way in to decompose it into side tables and such
... which normally leads to better performance. In addition, less
application coding needs to be done in order to decompose/compose so
that saves $$ in application costs.

Larry E.

I think you have to differentiate between the XML discussion and the
technology discussion.

XML is everywhere. Many documents are passed between companies using XML
and for legal reasons they must be stored as they are.
Now you have to decide to either operate on that XML as it is, or push
it into the relational model. The later in the very least duplicates
your storage requirements.
Now that is one aspect. Another aspect is that XML is inherently way
more flexible and more robust that the rigid relational layout where
every schema evolution has be well thought through.
Examples for areas with high levels of schema evolution are:
Taxes - New York (city??) is handling taxes in XML now.
Insurance - Insurance rules keep evolving and you need to preserve the
old ones while adding new ones.
So to that end XQuery is used to query the XML as is.

Now pureXML is IBM's labeling for the way the XML is stored in the
database. Anyone vendor who has a type "XML" can claim "native support",
but that says nothing about the quality of the implementation.
So by "pureXML" IBM means that the document is neither shredded into
relational, nor laid down as a text (or compressed binary) string.
Instead, as Larry notes, it is layed down in a hierarchical format which
matches XML's natural makeup.

How much room there is for good and bad performance is nicely
illustrated by another vendor who claims a 15x performance improvement
upon their already "native" XML between two releases....

If you are interesting in performance measuring and benchmarking pureXML
against other vendors take a look at:
http://tpox.sourceforge.net

Cheers
Serge