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Re: Autoexpanding ZIP archives?

From: Michael Sinz <Michael.Sinz_at_sinz.org>
Date: 2005-12-08 05:28:29 CET

Peter N. Lundblad wrote:
> On Wed, 7 Dec 2005, Malcolm Rowe wrote:
>>On Wed, Dec 07, 2005 at 12:49:20PM -0500, John Peacock wrote:
>>Note that the same argument essentially applies to any structured
>>document for which there is a 'better' (more space efficient, better able
>>to represent changes) delta mechanism than a binary diff: zip files,
>>compound OLE documents (e.g., Microsoft Office files), XML files,
>>potentially even C code.
> Why wouldn't the binary diff algorithm be suitable for XML documents?

I think people are talking by/past each other here. There are really
two different "diff" methods/algorithms involved here.

The one that is very visible is that of "svn diff" which currently only
works in line mode on text files. This is also the diff and merge/patch
mechanism within Subversion's merging feature.

There is also the diff "svndiff" mechanism(s) that are used in the backend
storage system. This algorithm is binary in nature and treats all files
the same. Its main purpose is to provide some level of delta compression
for the revision histories of files, be they text or xml or whatever.

On the front-end side of things, having better and more plugable diff
mechanisms (and merge/patch) would be a major win, especially when you
start dealing with specialized methods for certain file types.

The backend just needs to provide reasonable performance, reasonable
storage efficiency, and absolute reliability/reproduceability.

So, be careful when one talkes about XML documents vs binary diff vs
the line-by-line diff of "svn diff" since they are not all within the
same domain of the Subversion system/problem set.

Michael Sinz                     Technology and Engineering Director/Consultant
"Starting Startups"                                mailto:michael.sinz@sinz.org
My place on the web                            http://www.sinz.org/Michael.Sinz
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Received on Thu Dec 8 05:29:42 2005

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