XOM API for Processing XML with Java

[Elliotte Rusty Harold <elharo AT metalab.unc.edu>]

I've had an open action item for a while to consider whether 
additional namespace declarations should be reported to the 
NodeFactory so they can be filtered. Doing this would be really messy 
because XOM doesn't have any namespace class. What I came up with 
looked something like this:

public void makeNamespaceDeclaration(Element parent, String uri, String 
prefix)

This method would have to add the relevant namespace declaration to 
the passed Element. I also considered reworking the makeAttribute 
method to behave similarly.

However, today I think I finally convinced myself this was a bad idea 
for several reasons:

1. It's ugly as hell, and doesn't follow the Factory design pattern, 
or the general pattern of NodeFactory.

2. If you do need to muck with the additional namespace declarations, 
you can do it in endElement.

3. This is the kicker: I don't think depending on additional 
namespace declarations makes sense within XOM. They're tracked, and 
you can use them, but that's mostly for serialization. The right way 
to determine which namespace is in scope is by asking an element. 
Namespaces themselves don't really have any existence independent of 
the elements. Thus you shouldn't be filtering with respect to 
additional namespaces. (Filtering by element namespaces is perfectly 
OK, and supported now.) Furthermore, in practice additional 
namespaces often appear at the particular points they do simply to 
avoid having to be redeclared on several child elements in the same 
namespace. Their location has little if any meaning to the document 
itself. If you really want to adjust the additional namespaces, you 
can do it in endElement() anyway. They're just won't be a special 
callback for it.

Anyway, that's my thinking on this. It's a little blurred but I think 
I'm happy with it. However, if anyone wants to disagree or has a 
streaming use case that really needs to see additional namespace 
declaration in their own method, now is the time to speak up.


--

  Elliotte Rusty Harold
  elharo AT metalab.unc.edu
  Effective XML (Addison-Wesley, 2003)
  http://www.cafeconleche.org/books/effectivexml
  http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA