to OSM objects and the terms of an incoming query in order to make sure, they
can be matched appropriately.
-Nominatim offers different tokenizer modules, which behave differently and have
-different configuration options. This sections describes the tokenizers and how
-they can be configured.
+Nominatim currently offers only one tokenizer module, the ICU tokenizer. This section
+describes the tokenizer and how it can be configured.
!!! important
- The use of a tokenizer is tied to a database installation. You need to choose
+ The selection of tokenizer is tied to a database installation. You need to choose
and configure the tokenizer before starting the initial import. Once the import
is done, you cannot switch to another tokenizer anymore. Reconfiguring the
chosen tokenizer is very limited as well. See the comments in each tokenizer
section.
-## Legacy tokenizer
-
-The legacy tokenizer implements the analysis algorithms of older Nominatim
-versions. It uses a special Postgresql module to normalize names and queries.
-This tokenizer is automatically installed and used when upgrading an older
-database. It should not be used for new installations anymore.
-
-### Compiling the PostgreSQL module
-
-The tokeinzer needs a special C module for PostgreSQL which is not compiled
-by default. If you need the legacy tokenizer, compile Nominatim as follows:
-
-```
-mkdir build
-cd build
-cmake -DBUILD_MODULE=on
-make
-```
-
-### Enabling the tokenizer
-
-To enable the tokenizer add the following line to your project configuration:
-
-```
-NOMINATIM_TOKENIZER=legacy
-```
-
-The Postgresql module for the tokenizer is available in the `module` directory
-and also installed with the remainder of the software under
-`lib/nominatim/module/nominatim.so`. You can specify a custom location for
-the module with
-
-```
-NOMINATIM_DATABASE_MODULE_PATH=<path to directory where nominatim.so resides>
-```
-
-This is in particular useful when the database runs on a different server.
-See [Advanced installations](../admin/Advanced-Installations.md#importing-nominatim-to-an-external-postgresql-database) for details.
-
-There are no other configuration options for the legacy tokenizer. All
-normalization functions are hard-coded.
-
## ICU tokenizer
The ICU tokenizer uses the [ICU library](http://site.icu-project.org/) to
See the [Token analysis](#token-analysis) section below for more
information.
-During query time, only normalization and transliteration are relevant.
-An incoming query is first split into name chunks (this usually means splitting
-the string at the commas) and the each part is normalised and transliterated.
-The result is used to look up places in the search index.
+During query time, the tokeinzer is responsible for processing incoming
+queries. This happens in two stages:
+
+1. During **query preprocessing** the incoming text is split into name
+ chunks and normalised. This usually means applying the same normalisation
+ as during the import process but may involve other processing like,
+ for example, word break detection.
+2. The **token analysis** step breaks down the query parts into tokens,
+ looks them up in the database and assignes them possible functions and
+ probabilities.
+
+Query processing can be further customized while the rest of the analysis
+is hard-coded.
### Configuration
Here is an example configuration file:
``` yaml
+query-preprocessing:
+ - normalize
normalization:
- ":: lower ()"
- "ß > 'ss'" # German szet is unambiguously equal to double ss
The configuration file contains four sections:
`normalization`, `transliteration`, `sanitizers` and `token-analysis`.
+#### Query preprocessing
+
+The section for `query-preprocessing` defines an ordered list of functions
+that are applied to the query before the token analysis.
+
+The following is a list of preprocessors that are shipped with Nominatim.
+
+##### normalize
+
+::: nominatim_api.query_preprocessing.normalize
+ options:
+ members: False
+ heading_level: 6
+ docstring_section_style: spacy
+
+
#### Normalization and Transliteration
The normalization and transliteration sections each define a set of
##### split-name-list
-::: nominatim.tokenizer.sanitizers.split_name_list
+::: nominatim_db.tokenizer.sanitizers.split_name_list
options:
members: False
heading_level: 6
##### strip-brace-terms
-::: nominatim.tokenizer.sanitizers.strip_brace_terms
+::: nominatim_db.tokenizer.sanitizers.strip_brace_terms
options:
members: False
heading_level: 6
##### tag-analyzer-by-language
-::: nominatim.tokenizer.sanitizers.tag_analyzer_by_language
+::: nominatim_db.tokenizer.sanitizers.tag_analyzer_by_language
options:
members: False
heading_level: 6
##### clean-housenumbers
-::: nominatim.tokenizer.sanitizers.clean_housenumbers
+::: nominatim_db.tokenizer.sanitizers.clean_housenumbers
options:
members: False
heading_level: 6
##### clean-postcodes
-::: nominatim.tokenizer.sanitizers.clean_postcodes
+::: nominatim_db.tokenizer.sanitizers.clean_postcodes
options:
members: False
heading_level: 6
##### clean-tiger-tags
-::: nominatim.tokenizer.sanitizers.clean_tiger_tags
+::: nominatim_db.tokenizer.sanitizers.clean_tiger_tags
options:
members: False
heading_level: 6
#### delete-tags
-::: nominatim.tokenizer.sanitizers.delete_tags
+::: nominatim_db.tokenizer.sanitizers.delete_tags
options:
members: False
heading_level: 6
#### tag-japanese
-::: nominatim.tokenizer.sanitizers.tag_japanese
+::: nominatim_db.tokenizer.sanitizers.tag_japanese
options:
members: False
heading_level: 6
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