[OSM-dev] Timestamp in PBF files

Jochen Topf jochen at remote.org
Tue Dec 4 06:50:03 GMT 2012

On Tue, Dec 04, 2012 at 12:09:16AM +0100, Frederik Ramm wrote:
> On 03.12.2012 22:27, Jochen Topf wrote:
> >Why the "osmosis" in there? That seems rather strange to me. Either it is some
> >general thing that works with all programs, then it shouldn't be named after a
> >specific program. Or it is not, then it shouldn't be in a general file standard.
> It is the replication technology used by Osmosis on the server side.
> It works with all programs that use the Osmosis algorithm. It
> doesn't work with every thinkable replication mechanism because
> those might require other data. Trying to invent something "future
> proof" seldom works.
> For example, the way the directories are structured below the
> replication URL (http://planet.openstreetmap.org/replication/minute/000/118/578.osc.gz)
> is something specific to the way Osmosis handles its replication; a
> program that consumes these files needs knowledge about that.
> If you wanted to encode some kind of generic replication information
> then you'd probably boil it down to a simple string field called
> "replication_information" and that would then contain something like
> "replication_type=osmosis sequence_number=1234
> url=http://something/replication/minute" or so.
> That would be possible, but it would force every single
> writer/consumer of these files to serialize/deserialize the
> replication information string (tabs or spaces? spaces allowed after
> the equal sign or not? order significant? type=osmosis or
> type=Osmosis? ...) - making them top-level fields saves us from
> that.

That still isn't specific to Osmosis. Somebody else could implement this
algorithm. Markus seems to have done so, albeit a bit differently. The
algorithm should be documented somewhere and if you think there can be
other algorithms, maybe this one should get a name. But it should not be
named after one of the programs that happen to implement it.

This is a similar issue as with the main OSM map, which was named "Mapnik"
after the rendering program which lead to no end of confusion.

Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298

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