Re: [xml] lazy libxml

[Daniel Veillard <veillard redhat com>]

On Mon, Jun 19, 2006 at 01:50:42PM +0100, Nic James Ferrier wrote:
> I want a lazy implementation of libxml for my XRT project.
> 
> I am collecting my thoughts on how to build lazyness into libxml2.
> 
> If anyone has any views on how to do it, or has already done any work
> on it then please contact me, or make suggestions on this thread.
> 
> 
> 
> For those of you who don't know... lazy xml is the introduction of
> delayed computation of XML trees inside the dom. This means that you
> can have a part of the tree that is not known until the tree is
> serialized or until nodes within the tree are required.
> 
> For example, pseudo-code:
> 
>    DOM x = new DOM()
>    El  a = x.new_element_child("a")
>    El a_b = a.new_element_child(lazy_element("b"))
> 
> at this point a_b is not computed, it is present in the tree and it's
> type is known but the content, it's length and all the other details
> are hidden from view, indeed, they do not yet exist.
> 
> If we now do:
> 
>    print x.content()
> 
> then that causes element a_b to be serialized and thus the computation
> that produces the tree must be run and we get the correct output.
> 
> 
> So, really, lazy XML is just a way of introducing a sub-type into the
> libxml2 type definitions to indicate whether an object is computed or
> not. A function pointer will have to be stored with the object to
> provide the implementation of the node.
> 
> This is pretty simple to do at the C level but it gets more
> complicated if nodes are implemented in a higher level language,
> Python say.

  The problem is that libxml2 core won't be aware of that subtype.
And adding a node type to libxml2 is not something I would do lightly.
I don't really understand what it is aiming at honnestly, nor the extend
of your question. You can always add up a function in the _private field
of a node, but that will only be interpreted by non-libxml2 code by
definition.

Daniel

-- 
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veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
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