[Geocoding] Word order in query

[Sarah Hoffmann]

Hi,

On Sat, Jun 01, 2013 at 04:47:08PM +0200, Dariusz Bączkowski wrote:
> Hello,
> 
> I have noticed strange behavior on Nominatim. In some queries word ordering do 
> not have impact on results in some it has. Below are 2 examples of this 
> inconsistency. Should this queries return identical results? Is this a bug or 
> there is some architectural explanation for it? Can it be fixed?

It is more of an architectural thing. To Nominatim, these two queries are vastly
different. One is a search for a full name ("Konstantego Ildefonsa Gałczyńskiego"
is tagged exactly like that), for the other one it has to look for partial
matchings because it has the name backwards in its database. To keep the search 
load acceptable, Nominatim doesn't go through all potential partial matchings, 
so wether or not you get a result depends on how far down the list the right 
query is.

To see what I mean have a look at the debug output:
(1) http://nominatim.openstreetmap.org/search.php?q=Ga%C5%82czy%C5%84skiego+Konstantego+Ildefonsa%2C+Koszalin&debug=1
(2) http://nominatim.openstreetmap.org/search.php?q=Wyszy%C5%84skiego+Kardyna%C5%82a+Stefana%2C+Koszalin&debug=1

You can ignore most of the noise. Just have a look at the large table, it
contains the final queries that are sent to the DB. The query that would return
a result is in both cases the one with the three parts in the name column
(a partial query made up of three single words is needed). For (2) that query
is at rank 6, so it will still be evaluated. In (1) it ended up at rank 7 (because
there actually is a road called "Gałczyńskiego Konstantego Ildefonsa" somewhere
even though it is not the one in Koszalin) and you can see below that Nominatim
stops after rank 6.

There is certainly some room for improvement in the ranking of these search
queries especially when it comes to partial searches but in the end it is always
a question of weighing performance against completeness.

Sarah


> 
> Konstantego Ildefonsa Gałczyńskiego, Koszalin (RESULT)
> http://nominatim.openstreetmap.org/search.php?q=Konstantego+Ildefonsa+Ga%C5%82czy%C5%84skiego%2C+Koszalin&viewbox=-94.93%2C46.2%2C94.93%2C-46.2
> 
> Gałczyńskiego Konstantego Ildefonsa, Koszalin (NO RESULT)
> http://nominatim.openstreetmap.org/search.php?q=Ga%C5%82czy%C5%84skiego+Konstantego+Ildefonsa%2C+Koszalin&viewbox=16.18%2C54.2%2C16.2%2C54.19
> 
> Kardynała Stefana Wyszyńskiego, Koszalin (RESULT)
> http://nominatim.openstreetmap.org/search.php?q=Kardyna%C5%82a+Stefana+Wyszy%C5%84skiego%2C+Koszalin&viewbox=16.17%2C54.2%2C16.19%2C54.18
> 
> Wyszyńskiego Kardynała Stefana, Koszalin (RESULT)
> http://nominatim.openstreetmap.org/search.php?q=Wyszy%C5%84skiego+Kardyna%C5%82a+Stefana%2C+Koszalin&viewbox=-112.5%2C46.2%2C112.5%2C-46.2
> 
> -- 
> Pozdrawiam,
> Dariusz Bączkowski
> 
> ESYSCODER Dariusz Bączkowski
> e-mail: biuro at esyscoder.pl
> tel.: +48 720 820 220
> fax: +48 947 166 554
> http://esyscoder.pl/
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