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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 ...) <br>
<br>
So, again in English:<br>
<i>>>Honestly, for me this cause has become too complex, so I
won't vote (for now).<br>
In my understanding there is one k.o. criterium, mentioned by
Walter in the German forum ([1], post #81). He objected that there
are problems with SQL queries and the HSTORE scheme, Georg agreed
([2], 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'.<<</i><br>
<br>
<br>
And now, to make up for my blunder, here is a (rough) translation of
Walters and Georgs posts in the German forum:<br>
<br>
'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).<br>
All postgresql specific HSTORE queries, changes, indexing -
everything - only can work with complete keys, the values can be
arbitrary [3].<br>
Queries like "<i>List all nodes with the key 'maxspeed' or
'maxspeed:wet'</i>" are no problem at all, but a query like "<i>List
all nodes with 'maxspeed%'</i>" doesn't work! (% is the wildcard
for SQL).<br>
Queries for values (what stands behind the "=") can be done easily
and with good performance, too.<br>
In other words: <b>The database the entire OSM data is kept on
doesn't support variable keys when tagging.</b> You can save them
but you cannot query them.'<br>
[...]'<br>
<br>
<br>
And here Georgs (shortened) reply:<br>
<br>
'[...]<br>
The problem of variable database keys (which coincide with the OSM
keys) mentioned by Walter persists.<br>
Therefore: Variable conditions in the key prevent meaningful
database queries [...]. Variable conditions in the value on the
other hand remain a matter of applications'<br>
<br>
<br>
<br>
Sorry for the mess,<br>
Seoman<br>
<br>
<br>
[1] <a
href="http://forum.openstreetmap.org/viewtopic.php?pid=252489#p252489">http://forum.openstreetmap.org/viewtopic.php?pid=252489#p252489</a><br>
[2] <a class="moz-txt-link-freetext"
href="http://forum.openstreetmap.org/viewtopic.php?pid=252834#p252834">http://forum.openstreetmap.org/viewtopic.php?pid=252834#p252834</a>
<br>
[3] <a href="http://www.postgresql.org/docs/9.1/static/hstore.html">http://www.postgresql.org/docs/9.1/static/hstore.html</a><br>
<br>
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