XOM API for Processing XML with Java

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

Thanks for the background, Mike.

Wolfgang.

On Oct 31, 2006, at 11:12 AM, Michael Kay wrote:

> > The way the saxon binding works is to predeclare
> > all ns declarations on XQuery setup, rather than via a
> > lookup(String) callback, as in Jaxen or JAXP. That's why I'd
> > need something like
> > getNamespaces() rather than lookup(String).
>
> The main reason Saxon needs access to all the in-scope namespaces,  
> rather
> than just a prefix-to-uri lookup method, is so that it can compile  
> code to
> do the prefix-to-uri mapping at run-time, without retaining  
> references to
> compile-time objects. There are only two constructs in standard  
> XQuery that
> need the mapping at run-time, namely computed element and attribute
> constructors, but there are a lot more in XSLT and of course Saxon  
> uses the
> same mechanisms; there are also extensions such as saxon:evaluate()  
> that use
> the namespace context dynamically.
>
> Saxon's StaticQueryContext does in fact have a
> setExternalNamespaceResolver() method, which will be used to look  
> up any
> namespace prefixes that have not been actively declared: but  
> looking at the
> code I'm not sure that it currently supports these run-time uses of
> namespace prefixes. And in any case the NamespaceResolver interface  
> itself
> has an iteratePrefixes() method which doesn't map onto anything in  
> XOM's
> XPathContext.
>
> (If you want to see a really badly designed interface, look at JAXP's
> javax.xml.namespace.NamespaceContext which for some weird reason  
> allows you
> to iterate over all the prefixes bound to a particular URI, but  
> doesn't
> allow you to get all the in-scope prefixes!)
>
> Michael Kay