XOM API for Processing XML with Java

[Wolfgang Hoschek <wolfgang.hoschek AT mac.com>]

> You can get a list of the namespaces in scope on an element using an
> XPath query such as
>
> Nodes namespaces = element.query("namespace::node()");
>
> This still ascends the tree, but at least you don't have to write your
> own code for doing so.
>
> I've written a simple benchmark to see just how bad the various  
> methods
> for iterating over namespaces really are.
>
> https://xom.dev.java.net/source/browse/xom/src/nu/xom/benchmarks/ 
> NamespaceLister.java?rev=1.1&view=markup
>
> I'm not finished yet, but so far I'm not sure there's a practical
> problem here. In my tests against http://www.rddl.org/ this code is  
> able
> to retrieve each and every namespace URI, both in scope and declared,
> for every element in the document in between .1 and .3 seconds. No
> caching is done. i.e. each element is treated independently of the
> others. Thus the time to retrieve namespaces declared or in scope for
> just one element would be a small fraction of that.

That doc is 50KB small, right? If so, that would mean about 500KB/s  
throughput - unusable from my point of view by about 2 orders of  
magnitude for non-XOM-core serialization algorithms related to XPath,  
XQuery, STAX, bnux, etc., as those need to iterate over the declared  
namespaces. I certainly wouldn't use anything like that.

Also note that element.query("namespace::node()") is inefficient for  
reasons that have nothing to do with namespace iteration, but rather  
with XPath setup.

Wolfgang.