Re: [xml] lazy libxml

[Daniel Veillard <veillard redhat com>]

On Tue, Jun 20, 2006 at 09:51:00AM +0100, Nic James Ferrier wrote:
> XRT has to handle all types of content though, not just XML. I would
> like XRT to be able to handle binary types (like raster images) by
> representing them as XML binary objects (as Tim Bray has suggested)
> thusly:
>
>   <element xml:binary="base64">
>      RUlQOiAwMDczOls8YTAxOThlMGE+XSBDUFU6IDAgTm90IHRhaW50ZWQgRVNQOiAwMDdiOmEwMjNi
[..]

  If I remember that blog from last year it wqas really intended only
for minimal size blob, like an icon or a thumbnail. Oh and using the
xml namespace for something not coming from a W3C recommendation is a
very risky business.

> Consider this example of imagined XRT:
>
>    <xsl:variable name="pngfile"  select="lazy.get('adabyron.png')"/>
>    
>    <xsl:variable name="jpgfile" select="lazy.convert($pngfile, 'jpg')"/>
>
> The idea here is that there is a lazy object representing the
> pngfile which is then converted to another lazy object which
> represents a jpg file.

  Embedding the full image in the XML does not make sense to me:

    - it's inefficient in bandwidth (HTTP can transport binary fine)
    - it defeats all potential caching in HTTP from server to client

 Technologically this sounds wrong to me from an content service over HTTP
perspective, but my opinion is only that.

> Only when I do:
>
>    <xsl:value-of select="$jpgfile"/>
>
> does the actual import of the png file and it's conversion to jpg
> actually happen.

  And since all the generation there is really driven by low level 
libxml2 C code that's where the conversion woult had to be done.

> > 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.
>
> That's right. This would seem to be some scary fundamental change.
>
> What I would have to do is replace all the code which currently
> handles the content of a node and make it check to see whether the
> node is delayed/lazy or not and if lazy, compute it.

  and this scattered all over the place, in libxml2 tree, XPath, and in
libxslt. I really don't see how to extend libxml2 model to put this in without
changes all other the code, a very risky business.

> FWIW SXML already has an understanding of lazy XML I believe:
>
>   http://okmij.org/ftp/Scheme/SXML.html

  first time I heard of SXML. Well they use high level language to 
process the content, adding this kind of extensions may be easier for them.

Daniel

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