Re: [xml-dev] RE: defining xml diff/changes in xml : XUpdate etc

[Brian OBrien <bobrien18@yahoo.com>]

Is there no way off this list??????



--- Robin Berjon <robin.berjon@expway.fr> wrote:

> On Apr 12, 2006, at 20:47, Adrian Mouat wrote:
> > The IETF had a bof on the subject of xml patching
> - the notes can  
> > be found here:
> >
> >
> http://www3.ietf.org/proceedings/05nov/xmlpatch.html
> >
> > Basically there seems to be no current support for
> the creation of  
> > a standard.
> 
> Have you taken a look at REX? It is not intended to
> be a generic XML  
> patch language, but since the list of supported
> events is to be made  
> open-ended, you could devise a set of events that
> correspond to  
> patching operations. It may not be an ideal
> solution, but it does  
> have strong support in terms of moving the standard
> forward so piggy- 
> backing that might be a good idea.
> 
> > Michael Kay wrote:
> >> * must the effect of applying diffs be
> independent of the order in  
> >> which
> >> they are applied?
> >
> > Surely impossible?? I can't add a node to a
> subtree that doesn't  
> > exist. Or do you have a completely different
> format in mind?
> 
> It depends on whether you have the constraint of
> being able to create  
> a WF XML document at each step, or if your patches
> can work on  
> intermediate in-memory representations that may not
> hold the entire  
> tree and may have ghost nodes. IIRC in theory MPEG-B
> updates can send  
> you fragment updates that are inside nodes that you
> don't yet have  
> (you would use the path to create stubs). In
> practice I'm not sure  
> it's fully supported, but I can ask.
> 
> >> * do diff files need to be human-readable?
> >
> > I think not - they can be transformed into human
> readable formats.
> 
> I guess the question is also about whether they have
> to be XML. I  
> think it's best but then I'm an integrist :)
> 
> >> * do diff files need to be small?
> >
> > Is XML ever?
> 
> Yes of course, just use an efficient XML format! Oh
> wait, it's not  
> Friday, sorry.
> 
> >> * what kind of changes need to be diff'ed? Do
> they include, for  
> >> example,
> >> renaming of nodes? Do they include any bulk
> changes, such as  
> >> deleting all
> >> instances of a particular attribute? Do they
> include changes at  
> >> the lexical
> >> level, e.g. changing the expansion text of an
> internal entity? Do  
> >> they
> >> include DTD changes?DUL doesn't handle
> expressions like this, and  
> >> I don't think it should - leave that to XQuery
> update.
> > Entities are a hard question - there are even more
> questions if you  
> > consider whether they should be resolved or not.
> DTD changes are  
> > not supported in DUL.
> 
> I would personally opt for supporting only what the
> XPath DM  
> supports, but I realise that this limits some of the
> use cases.
> 
> The EXI WG is working on a similar issue related to
> the fidelity of  
> efficient XML encodings, which is basically the
> issue of the Infoset,  
> namely what "matters" in an XML document. XML itself
> is defined  
> entirely at the syntax level, but for some problems
> if you stick just  
> to that you end up with good old gzip (for the
> efficient XML case) or  
> good old diff (for the diff case). Presumably there
> are use cases  
> that require more than what those options can bring
> to the table,  
> which is where things get interesting. Currently I'm
> working on a  
> scale measuring fidelity along the following lines.
> It is meant to  
> evaluate efficient XML formats, but I think it could
> be usefully  
> adapted to work on XML diff languages:
> 
>   -1: does not support "very basic" parts of the
> Infoset, such as PIs  
> or comments
>    0: supports what can be captured by the Infoset,
> except notations  
> (and perhaps unresolved entities -- under
> discussion)
>    1: supports everything that is captured by the
> Infoset
>    2: supports the Infoset plus items that the
> Infoset does not take  
> into account but that cannot be discounted as purely
> syntactic (e.g.  
> element and attribute declarations)
>    3: supports the above plus some completely
> syntactic constructs,  
> such as CDATA sections, all the way to perhaps
> attribute quote  
> characters, the variants in empty elements, or the
> amount of space  
> between attributes or between target and data.
> 
> There's still some fair amount of fuzz in there of
> course, but I'd be  
> very interested in feedback on the matter.
> 
> FYI REX could support renaming (by transmitting the
> corresponding DOM  
> mutation events) and batch changes (by using an
> XPath selector that  
> matches several nodes -- this is currently in the
> draft but I think  
> it'll be dropped).
> 
> -- 
> Robin Berjon
>     Senior Research Scientist
>     Expway, http://expway.com/
> 
> 
> 
>
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