[OSM-dev] History File Formats
brett at bretth.com
Wed May 11 14:31:00 BST 2011
With the recent discussions around deciding on file extensions (eg. osm,
osc, osh, pbf, etc) it seemed a good time to raise a question I've had for a
What is the relationship between osmChange (osc) files, and full history
files (osh?) with visible attributes?
When I first created the osc format for Osmosis, I also considered using the
visible attribute approach. At the time I decided against it for a couple
- I wanted to avoid confusion about what type of data is contained in a
- Code re-use and XML schema definition is more precise with osc because
the node/way/relation elements are always the same without optional elements
appearing in some formats and not others.
- At the time I considered the visible flag attribute an aspect of our
database implementation and not part of the OSM logical data model.
I then used the osc file format to create not only the commonly used
daily/hourly/minutely replication files, but also a complete dump of
database history updated daily (stored in one file per day).
I was slightly surprised then to see the creation of the new full history
files. Don't get me wrong, I don't have an issue with it and choice is
good. But I do wonder why we've now gone back to a single massive file
approach which is updated rarely and requires a full download each time when
the existing files allow incremental download of recent changes. Merging
all files into a single file can be done client-side if required without
much processing overhead.
It leaves me with a few questions:
- Are the Osmosis-based daily full history extracts even used? Should I
- Are the history extracts in an unsuitable format and hence unused?
- Should Osmosis switch over to using the osh format instead of osc to
represent change data?
- Does the full history single file contain additional useful data that
is required? Changesets perhaps?
What do people think?
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