Re: [xml] namespace handling

[Daniel Veillard <veillard redhat com>]

On Mon, May 12, 2003 at 06:09:49PM +0200, Kasimier Buchcik wrote:
> premise:
> If a namespace-node is created, libxml2 wants it to reference a
> namespace declaration (node->ns --> some-node->nsDef) existent in the
> ancestor-or-self axis.

  yes

>    Now, let's take some DOM 2 methods:
>    createElementNs(...)
>      If I create an element like this I have to ensure that the namespace
>      is available in libxml2 - even if I may never add this element to
>      a tree.
[...]
>      Are there any other solutions existent?

  Admit that DOM is severely broken as an API.

>    createAttributeNs(...)
>      Here it gets a bit messy: where to declare the namespace?
>      I cannot attach it to any nsDef since there might be no tree
>      existent yet (if building a tree from scratch).
>      Does a solution exist?

  No clean solution. Creating the Attribute/Element without any context
is a serious problem.

>    importNode(...)
>      If I import a tree (deep=true) into an other document and would use
>      xmlDocCopyNode, this function would lead to xmlStaticCopyNode and
>      xmlCopyProp being processed, both trying to reconciliate namespaces,
>      resulting in all namespaces being recreated at the given tree.
>      Adding this tree to the desired document would imply:
>        a. Leave the created namespaces - this could lead to a lot of
>           declarations.
>        b. OR try substitute the namespaces with proper namespaces in the
>           ancestor axis.

  Undefined in the spec. Do whatever.

>    removeChild(...)
>      If I detach a tree from the document, namespace references to
>      "out of the tree" may still exist. What to do?

 From the detached tree ? yes but it's not deletion. If deleting, then
no you should not have this problem if deletion is recursive.

> Considering these examples, I might doubt if libxml2's philosophy of
> handling namespaces is adequate for working with DOM 2 (or DOM 3).

  libxml2 namespace handling predates DOM2. It's far cleaner, i.e.
the href to prefix mapping is associated in a single place, it is also
more efficient in term of space requirement.

> So you may want to consider the following proposals:
>
> 1. A list of namespaces on the xmlDoc.

  Was okay with namespaces from 1998, completely useless with current
namespaces which are scope based I'm afraid.
  I don't think I'm ready to completely break libxml2 and libxslt code
to handle namespaces in a very different way. It would also impact 
all the APIs which work with xmlNsPtr, really no I don't think it's
an option at this point.

Daniel

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