XOM API for Processing XML with Java

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

At 9:38 AM -0400 6/18/03, John Cowan wrote:

> This is a classic datahead/dochead split, and the fact that you're
> ambivalent shows that you have some of each in your makeup.  :-)
> Dataheads think of an element as a container for its content, and
> if the container is removed, the content goes to Tumbolia with it.
> Docheads think of elements as basically annotations of ranges, and if
> the annotation is removed, the underlying content remains.
>
> I don't think you can make everyone happy here.  Just make sure that
> *some* path through the code makes it possible to do either operation.


I've been playing with the API, and I think something John suggested 
here is likely to work. First I'll rename makeElement to 
beginMakeElement and endElement to finishMakeElement. (Would 
beginMakingElement and finishMakingElement be more grammatical? or 
perhaps startMakingElement and finishMakingElement?)

Next, I'll move the actual attachment to the tree in XOMHandler into 
endElement instead of startElement. The element node will only be 
attached to the tree if finishMakeElement returns non-null. Thus 
returning null from beginMakeElement will remove the start-tag and 
end-tag, while leaving the contents intact. Returning null from 
finishMakeElement will remove the entire element including its 
contents. This is a more consistent API with no need to call detach.

The only downside I see to this approach is that it will no longer be 
possible to walk up the tree from the currently built element. For 
instance, it won't be possible to access the Document object that 
contains a node until after the entire document has been parsed. 
Looking at my samples, I don't think this is a major issue. Most use 
cases that require walking up the tree, normally have pretty random 
access that requires the entire tree to be in memory before beginning 
processing anyway. XSLT/XPath is the classic example. And if you 
really wanted to know what the ancestors were, you could always put a 
stack in the factory. Can anyone think of any problem that this new 
approach would make significantly more difficult to solve compared to 
the old approach?
--

  Elliotte Rusty Harold
  elharo AT metalab.unc.edu
  Processing XML with Java (Addison-Wesley, 2002)
  http://www.cafeconleche.org/books/xmljava
  http://www.amazon.com/exec/obidos/ISBN%3D0201771861/cafeaulaitA