[OSM-talk] What is an ID?

[Lester Caine]

Rather than comment on the id stability thread, I though it better to turn the 
question around ...

In my own data trail, an ID *IS* unique, and is directly linked to the piece of 
data it relates to. If I change the data then the version number goes up. If I 
delete the data, then the ID number remains since it identifies the HISTORY 
relating to that item. The idea that someone is going to 'reuse' id's because 
they are no being used raises alarm bells. I thought we had history relating to 
every element nowadays, so how do you know what the history relates to if you 
reuse the ID? Also the idea of 'renumbering' everything is equally alarming, 
given that every old changeset would have to be updated?

If we are running out of ID's, then a switch to 64 bit is an urgent requirement 
simply to prevent the existing data and history trail from being corrupted.

Now having said all that ... USING the internal ID for external purposes, while 
potentially practical, is not the most sensible way forward as has been 
highlighted in several ways. I'm probably in agreement on a 'link server' 
approach, but I think that there are a number of areas where additional 'ID's 
need to be stored in the database and managed in parallel. Postcodes, 
bus/tramstop id's, Airport codes, telephone area codes, and so on. We had a 
little discussion on parallel databases, and that slots in with the 'link 
server', but I think that in order to make ANY parallel database system work, 
then the core ID's have to be stable and consistent, even if they do return 
'deleted' ... at which point on needs to be able to ask 'why' and possibly roll 
back a change that should not have happened? If a item has history then it's ID 
can't be reused.

http://www.openstreetmap.org/browse/node/<xxx>/history simply has to be 
consistent? Then what may be missing IS a tag for 'split_from' or 'merged_with' 
but the linked ID's must also be consistent?

-- 
Lester Caine - G8HFL
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