Hi,
On 05/31/11 23:43, Sergey Galuzo wrote:
Obvious differences between full and change are explicit
create/modify/delete tags.
We have full history OSM files and normal OSM files (both use .osm
extension and <osm>...</osm>), and we have simple diffs and replication
diffs (both use .osc and <osmChange>...</osmChange>).
Normal OSM files never have a "visible" attribute, and they contain at
most one version of every object.
Objects in full history OSM files contain a "visible" attribute, and
these files may contain different versions of the same object, with at
most one having visible=true. If there is a version with visible=true,
it will be the highest numbered version of that object. They do not
necessarily contain a full sequence of versions, i.e. you could have a
full history file that only has versions 2 and 5 of something.
(There are also .osm files as written by the JOSM editor; these do not
have a "visible" attribute but may have an "action" attribute which, if
set to "delete", has a similar effect. This is a niche case.)
The diffs contain <delete>, <modify>, and <create> blocks. A version in
<create> is usually 1. (Current implementation means it is *always* 1
but this could be changed; it is not specified in the API that the first
version of something must always be 1.) A version in <create> or
<modify> can never have visible=false.
If you have full replication diffs then one diff can contain the same
object multiple times, with different version numbers. It is possible
for the same object to appear in the <create>, <modify>, and <delete>
section of the same replication diff. Versions are not guaranteed to be
sorted, i.e. you could first encounter version 6 in a <delete> block and
later encounter version 5 in a <modify>.
Since multiple edits are conflated in a simple diff, it is possible that
a simple diff contains an object as version 2 in a <modify> block but
the consumer has never before seen that object (because the version 1
that would have been in a <create> has happened in the same diff
interval as the modification to version 2).
In short, your assumption
var changeTag = !Visible ? "delete" : Version == 1 ? "create" : "modify";
is mostly true but it depends very much on the context in which you want
to use it; there's a lot of things to trip you over.
Bye
Frederik
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