XOM API for Processing XML with Java

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

On Sep 24, 2006, at 8:02 PM, Tatu Saloranta wrote:

> --- Elliotte Harold <elharo AT metalab.unc.edu> wrote:
>
> > Tatu Saloranta wrote:
> >
> > > On a related note: it is still possible to get
> > proper
> > > prefix rewriting on output (such that result is
> > output
> > > with localName/URI pairs being correct and there
> > being
> > > no prefix conflicts, which may require prefix
> > > changes),
> >
> > This should simply not be necessary. XOM does not
> > allow prefix
> > conflicts. If you can construct a document that
> > contains one using XOM,
> > then that's a bug; and I should fix it.
>
> So much for that idea then. ;-)

One would expect a repairing and non-repairing Stax XMLStreamWriter  
impl to yield equal output (wrt. Canonical XML) when serializing XOM  
documents, because a XOM document is guaranteed to be wellformed due  
too XOM's hard coded internal sanity checks. On assembling an  
Element, XOM already rejects namspace conflicts with wellformedness  
exceptions. In XOM, assembling an element is a stage that precedes  
serialization. In the serialization stage there are no namespace  
conflicts anymore, and nothing needs to be repaired. Thus, repairing  
mode (a standard feature of StAX) offers no benefits for serializing  
XOM documents.

However, XOM offers no automatic assistance to generate a namespace- 
wellformed document in the presence of actual or potential namespace  
conflicts (it simly rejects them with an exception to begin with).  
So, it is the responsibility of the client to figure out how to  
resolve conflicts on element construction, if any.

In contrast, repairing mode is part of a later stage, namely  
serialization, and intended to relieve the (typically non-XOM) client  
of such responsibility. Repairing mode moves the burden of "fixing  
up" conflicting namespaces with non-conflicting namespaces into the  
serializer (XMLStreamWriter), thus generating ns wellformed documents  
no matter what conflicting namespace info the client passes to the  
StAX writer.

In practise, the absense of a repairing mode often seems to be a non- 
issue, but sometimes the safety of repairing mode comes in handy. In  
particular when multiple independent third party library modules are  
all writing to the same element or document.

Wolfgang.