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add documentation for new query preprocessing

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Sarah Hoffmann
2024-12-13 16:53:08 +01:00
parent 2b87c016db
commit fbb6edfdaf
3 changed files with 101 additions and 27 deletions
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docs/customize/Tokenizers.md
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@@ -4,12 +4,11 @@ The tokenizer module in Nominatim is responsible for analysing the names given
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
@@ -43,10 +42,19 @@ On import the tokenizer processes names in the following three stages:
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
@@ -58,6 +66,8 @@ have no effect.
Here is an example configuration file:
``` yaml
query-preprocessing:
- normalize
normalization:
- ":: lower ()"
- "ß > 'ss'" # German szet is unambiguously equal to double ss
@@ -81,6 +91,22 @@ token-analysis:
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