Re: extracting location info from string - Mailing list pgsql-sql

On 05/22/2011 09:42 PM, Craig Ringer wrote:
> On 23/05/2011 9:11 AM, Andrej wrote:
>> On 23 May 2011 10:00, Tarlika Elisabeth Schmitz
>> <postgresql3@numerixtechnology.de> wrote:
>>> On Sun, 22 May 2011 21:05:26 +0100
>>> Tarlika Elisabeth Schmitz<postgresql3@numerixtechnology.de> wrote:
>>>
>>>> A column contains location information, which may contain any of the
>>>> following:
>>>>
>>>> 1) null
>>>> 2) country name (e.g. "France")
>>>> 3) city name, region name (e.g. "Bonn, Nordrhein-Westfalen")
>>>> 4) city name, Rg. region name (e.g. "Frankfurt, Rg. Hessen")
>>>> 5) city name, Rg region name (e.g. "Frankfurt, Rg Hessen")
>>>
>>>
>>> I also need to cope with variations of COUNTRY.NAME and REGION.NAME.

That isn't a table structure, that's a freeform text structure.  You didn't 
state your question, Tarlika, but your database structure is terrible.  For 
example, "region" and "country" should be different columns.  Really!

How you get your raw data into those columns can be interesting.

> This is a hard problem. You're dealing with free-form data that might be
> easily understood by humans, but relies on various contextual information and
> knowledge that makes it really hard for computers to understand.
>
> If you want to do a good job of this, your best bet is to plug in 3rd party
> address analysis software that is dedicated to this task. Most (all?) such

These aren't really addresses, as the OP presents them.

> packages are commercial, proprietary affairs. They exist because it's really,
> really hard to do this right.
>
>> Another thing of great import is whether the city can occur in the
>> data column all by itself; if yes, it's next to impossible to distinguish
>> it from a country.
>
> Not least because some places are both, eg:
>
> Luxembourg
> The Vatican
> Singapore
>
> (The Grand Duchy of Luxembourg has other cities, but still serves as an example).

And,of course, you have to distinguish the City of London from London.  New 
York City comprises five boroughs (counties), each of which is itself a city.  (Brooklyn is one of the largest cities
inthe world all by itself.) 
 
"Region" has different meanings in different areas - it can mean part of a 
county, or state / province, or nation, or continent.  "The Baltic region", 
"the Northeast", "upstate", "the North Country", "Europe" are all regions.

The OP should share more about the semantics of their problem domain and 
whether they really intend those table structures to be table structures.  Really?

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg