[Tagging] Extended Conditions - response to votes
hermanns at ptt.uni-due.de
Thu Jul 5 10:39:52 BST 2012
Sorry, I didn't realise I was on the 'Tagging' instead of the 'Talk-de'
list. And the first link was wrong, too ... (note to self: drink
coffee first, write to list afterwards ...)
So, again in English:
/>>Honestly, for me this cause has become too complex, so I won't vote
In my understanding there is one k.o. criterium, mentioned by Walter in
the German forum (, post #81). He objected that there are problems
with SQL queries and the HSTORE scheme, Georg agreed (, Post #89). I
don't understand much of this but I agree that the queries have to work
in every case. So my question is: Can anybody solve the problem
mentioned by Walter in favour of the proposal? I'm talking about a real
query test, not statements like 'that should work in theory'.<</
And now, to make up for my blunder, here is a (rough) translation of
Walters and Georgs posts in the German forum:
'In Postgresql (the database OSM uses internally) tags are stored in the
form key=value. In the Simple-/Snapshot scheme the so called HSTORE is
used for this; that is a data structure for depositing any number of
information of an object (i.e. the tags of a node/way).
All postgresql specific HSTORE queries, changes, indexing - everything -
only can work with complete keys, the values can be arbitrary .
Queries like "/List all nodes with the key 'maxspeed' or
'maxspeed:wet'/" are no problem at all, but a query like "/List all
nodes with 'maxspeed%'/" doesn't work! (% is the wildcard for SQL).
Queries for values (what stands behind the "=") can be done easily and
with good performance, too.
In other words: *The database the entire OSM data is kept on doesn't
support variable keys when tagging.* You can save them but you cannot
And here Georgs (shortened) reply:
The problem of variable database keys (which coincide with the OSM keys)
mentioned by Walter persists.
Therefore: Variable conditions in the key prevent meaningful database
queries [...]. Variable conditions in the value on the other hand remain
a matter of applications'
Sorry for the mess,
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