[OSM-dev] Representing differences between sets of OSM data

[Jon Burgess]

On Mon, 2007-08-20 at 08:46 +1000, Brett Henderson wrote:
>  From memory, one area that planetdiff is different is that it includes 
> the old and new versions of a modified entity.  Osmosis only includes 
> the new version.  Osmosis could include the old version but it adds 
> considerable complexity to database queries and is likely to adversely 
> affect performance.  I have no plans to do this unless there's a strong 
> requirement for it.

Yes the planetdiff includes both old and new objects. This is very
similar to the traditional unified diff format which list both added and
removed code blocks. This was a natural fit with the way the diff
algorithm operates and allows a high degree of confidence that we're
applying the diff on top of the correct file. 

In theory it would also allow a "-R" mode to remove a diff from a planet
dump and generate the previous one (I've not implemented this though).

I'll have to look a little more at the osmosis diffs. It would be good
to converge on a common format.

	Jon