of the input data before it is added to the search index. It comes with a
selection of sanitizers and token analyzers which you can use to adapt your
installation to your needs. If the provided modules are not enough, you can
-also provide your own implementations. This section describes how to do that.
+also provide your own implementations. This section describes the API
+of sanitizers and token analysis.
!!! warning
This API is currently in early alpha status. While this API is meant to
### Sanitizer configuration
::: nominatim.tokenizer.sanitizers.config.SanitizerConfig
- rendering:
- show_source: no
+ options:
heading_level: 6
-### The sanitation function
+### The main filter function of the sanitizer
-The sanitation function receives a single object of type `ProcessInfo`
+The filter function receives a single object of type `ProcessInfo`
which has with three members:
- * `place`: read-only information about the place being processed.
+ * `place: PlaceInfo`: read-only information about the place being processed.
See PlaceInfo below.
- * `names`: The current list of names for the place. Each name is a
- PlaceName object.
- * `address`: The current list of address names for the place. Each name
- is a PlaceName object.
+ * `names: List[PlaceName]`: The current list of names for the place.
+ * `address: List[PlaceName]`: The current list of address names for the place.
While the `place` member is provided for information only, the `names` and
`address` lists are meant to be manipulated by the sanitizer. It may add and
#### PlaceInfo - information about the place
::: nominatim.data.place_info.PlaceInfo
- rendering:
- show_source: no
+ options:
heading_level: 6
#### PlaceName - extended naming information
::: nominatim.data.place_name.PlaceName
- rendering:
- show_source: no
+ options:
heading_level: 6
-## Custom token analysis module
-Setup of a token analyser is split into two parts: configuration and
-analyser factory. A token analysis module must therefore implement two
-functions:
+### Example: Filter for US street prefixes
+
+The following sanitizer removes the directional prefixes from street names
+in the US:
+
+``` python
+import re
+
+def _filter_function(obj):
+ if obj.place.country_code == 'us' \
+ and obj.place.rank_address >= 26 and obj.place.rank_address <= 27:
+ for name in obj.names:
+ name.name = re.sub(r'^(north|south|west|east) ',
+ '',
+ name.name,
+ flags=re.IGNORECASE)
+
+def create(config):
+ return _filter_function
+```
+
+This is the most simple form of a sanitizer module. If defines a single
+filter function and implements the required `create()` function by returning
+the filter.
+
+The filter function first checks if the object is interesting for the
+sanitizer. Namely it checks if the place is in the US (through `country_code`)
+and it the place is a street (a `rank_address` of 26 or 27). If the
+conditions are met, then it goes through all available names and
+removes any leading directional prefix using a simple regular expression.
+
+Save the source code in a file in your project directory, for example as
+`us_streets.py`. Then you can use the sanitizer in your `icu_tokenizer.yaml`:
+
+``` yaml
+...
+sanitizers:
+ - step: us_streets.py
+...
+```
+
+!!! warning
+ This example is just a simplified show case on how to create a sanitizer.
+ It is not really read for real-world use: while the sanitizer would
+ correctly transform `West 5th Street` into `5th Street`. it would also
+ shorten a simple `North Street` to `Street`.
+
+For more sanitizer examples, have a look at the sanitizers provided by Nominatim.
+They can be found in the directory
+[`nominatim/tokenizer/sanitizers`](https://github.com/osm-search/Nominatim/tree/master/nominatim/tokenizer/sanitizers).
+
+
+## Custom token analysis module
::: nominatim.tokenizer.token_analysis.base.AnalysisModule
- rendering:
- show_source: no
+ options:
heading_level: 6
::: nominatim.tokenizer.token_analysis.base.Analyzer
- rendering:
- show_source: no
+ options:
heading_level: 6
+
+### Example: Creating acronym variants for long names
+
+The following example of a token analysis module creates acronyms from
+very long names and adds them as a variant:
+
+``` python
+class AcronymMaker:
+ """ This class is the actual analyzer.
+ """
+ def __init__(self, norm, trans):
+ self.norm = norm
+ self.trans = trans
+
+
+ def get_canonical_id(self, name):
+ # In simple cases, the normalized name can be used as a canonical id.
+ return self.norm.transliterate(name.name).strip()
+
+
+ def compute_variants(self, name):
+ # The transliterated form of the name always makes up a variant.
+ variants = [self.trans.transliterate(name)]
+
+ # Only create acronyms from very long words.
+ if len(name) > 20:
+ # Take the first letter from each word to form the acronym.
+ acronym = ''.join(w[0] for w in name.split())
+ # If that leds to an acronym with at least three letters,
+ # add the resulting acronym as a variant.
+ if len(acronym) > 2:
+ # Never forget to transliterate the variants before returning them.
+ variants.append(self.trans.transliterate(acronym))
+
+ return variants
+
+# The following two functions are the module interface.
+
+def configure(rules, normalizer, transliterator):
+ # There is no configuration to parse and no data to set up.
+ # Just return an empty configuration.
+ return None
+
+
+def create(normalizer, transliterator, config):
+ # Return a new instance of our token analysis class above.
+ return AcronymMaker(normalizer, transliterator)
+```
+
+Given the name `Trans-Siberian Railway`, the code above would return the full
+name `Trans-Siberian Railway` and the acronym `TSR` as variant, so that
+searching would work for both.
+
+## Sanitizers vs. Token analysis - what to use for variants?
+
+It is not always clear when to implement variations in the sanitizer and
+when to write a token analysis module. Just take the acronym example
+above: it would also have been possible to write a sanitizer which adds the
+acronym as an additional name to the name list. The result would have been
+similar. So which should be used when?
+
+The most important thing to keep in mind is that variants created by the
+token analysis are only saved in the word lookup table. They do not need
+extra space in the search index. If there are many spelling variations, this
+can mean quite a significant amount of space is saved.
+
+When creating additional names with a sanitizer, these names are completely
+independent. In particular, they can be fed into different token analysis
+modules. This gives a much greater flexibility but at the price that the
+additional names increase the size of the search index.
+
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