From: Sam Roberts <sroberts@...>
Date: 2003-06-28T10:22:36+09:00
Subject: Re: REXML and Namespaces.


This seems similar to APIs in XOM, which I've been reading about. Have
you looked at it, and the design discussion behind it?

  http://www.cafeconleche.org/XOM/

Sam

Quoteing ser@germane-software.com, on Sat, Jun 28, 2003 at 04:30:34AM +0900:
> > the element "b" would get the w3.org namespace, and foo:a would get the
> > foo.org namespace.
> 
> This is an interesting idea.  I was thinking along the same lines, but
> with setting the context in the node tree itself:
> 
>    a = doc.add_element("a")          # New element, no namespace
>    a.define_namespace( "foo", "http://foo.org/b" ) 
>                                      # Assoc. namespace w/ prefix
>    a.namespace = "http://foo.org/b"  # Set a's namespace 
>    b = a.add_element("b")        # Add b to a; no default (no) 
>                                  # namespace
>    c = a.add_element("c", "http://x.org") 
>                                  # Add c to a in x.org namespace
>    d = c.add_element("d")        # Add d to c, in default (x.org) 
>                                  # namespace
>    e = c.add_element("e", '')    # Add e to c, w/ empty namespace
> 
> My hesitation with doing things this way is that it marginalizes
> prefixes, which is how XML is defined.  However, it is not the way
> people think about namespaces.  It also hides the nature of default
> namespaces, which I really don't like.
> 
> > A sidenote: Sean, I'd like to pick your brain some time, since I'm
> > planning to set up a way of indexing content of XML documents in a
> > separate index file, and it may make XPath searches much faster and add
> > the possibly of disk-based access instead of parse-whole-tree access of
> > docs for XPath.
> 
> If you can think of a way to do this, I'd really like to hear about
> it.  At one point I wrote a version of XPath that used indexed trees,
> in the hopes that I could speed it up.  I discovered that the time
> consuming aspects of XPath are things that are not indexable:
> predicates.  Predicates must be evaluated in the context of a node. 
> Ironically, having to deal with namespaces also really slows down
> XPath searches.  In the end, the cost of indexing a document offset
> any speed gains the indexing provided; in fact, for simple 'a/b'
> XPaths, the indexed version was only faster where the indexing cost
> was amortized over multiple searches.
> 
> It sounds like you've got something in mind that bypasses parsing the
> XML document at all, which would be interesting; to be honest, I can't
> imagine how you could evaluate an XPath in that context, but feel free
> to email me about it -- I'd love to hear your ideas.
> 
> --- SER
>