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25 lines
1.2 KiB
Markdown
25 lines
1.2 KiB
Markdown
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# Basic Architecture
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Nominatim provides geocoding based on OpenStreetMap data. It uses a Postgresql
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database as a backend for storing the data.
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There are three basic parts to Nominatim's architecture: the data import,
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the address computation and the search frontend.
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The __data import__ stage reads the raw OSM data and extracts all information
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that is useful for geocoding. This part is done by osm2pgsql, the same tool
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that can also be used to import a rendering database. It uses the special
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gazetteer output plugin in `osm2pgsql/output-gazetter.[ch]pp`. The result of
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the import can be found in the database table `place`.
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The __address computation__ or __indexing__ stage takes the data from `place`
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and adds additional information needed for geocoding. It ranks the places by
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importance, links objects that belong together and computes addresses and
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the search index. Most of this work is done in Pl/pqSQL via database triggers
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and can be found in the file `sql/functions.sql`.
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The __search frontend__ implements the actual API. It takes queries for
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search and reverse geocoding queries from the user, looks up the data and
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returns the results in the requested format. This part is written in PHP
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and can be found in the `lib/` and `website/` directories.
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