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.
-## Using non-standard sanitizers and token analyzers
+!!! warning
+ This API is currently in early alpha status. While this API is meant to
+ be a public API on which other sanitizers and token analyzers may be
+ implemented, it is not guaranteed to be stable at the moment.
-Sanitizer names (in the `step` property) and token analysis names (in the
-`analyzer`) may refer to externally supplied modules. There are two ways
+
+## Using non-standard modules
+
+Sanitizer names (in the `step` property), token analysis names (in the
+`analyzer`) and query preprocessor names (in the `step` property)
+may refer to externally supplied modules. There are two ways
to include external modules: through a library or from the project directory.
To include a module from a library, use the absolute import path as name and
somewhere in your project directory and then use the relative path to the
file. Include the whole name of the file including the `.py` ending.
+## Custom query preprocessors
+
+A query preprocessor must export a single factory function `create` with
+the following signature:
+
+``` python
+create(self, config: QueryConfig) -> Callable[[list[Phrase]], list[Phrase]]
+```
+
+The function receives the custom configuration for the preprocessor and
+returns a callable (function or class) with the actual preprocessing
+code. When a query comes in, then the callable gets a list of phrases
+and needs to return the transformed list of phrases. The list and phrases
+may be changed in place or a completely new list may be generated.
+
+The `QueryConfig` is a simple dictionary which contains all configuration
+options given in the yaml configuration of the ICU tokenizer. It is up to
+the function to interpret the values.
+
+A `nominatim_api.search.Phrase` describes a part of the query that contains one or more independent
+search terms. Breaking a query into phrases helps reducing the number of
+possible tokens Nominatim has to take into account. However a phrase break
+is definitive: a multi-term search word cannot go over a phrase break.
+A Phrase object has two fields:
+
+ * `ptype` further refines the type of phrase (see list below)
+ * `text` contains the query text for the phrase
+
+The order of phrases matters to Nominatim when doing further processing.
+Thus, while you may split or join phrases, you should not reorder them
+unless you really know what you are doing.
+
+Phrase types (`nominatim_api.search.PhraseType`) can further help narrowing
+down how the tokens in the phrase are interpreted. The following phrase types
+are known:
+
+::: nominatim_api.search.PhraseType
+ options:
+ heading_level: 6
+
+
## Custom sanitizer modules
A sanitizer module must export a single factory function `create` with the
### Sanitizer configuration
-::: nominatim.tokenizer.sanitizers.config.SanitizerConfig
- rendering:
- show_source: no
+::: nominatim_db.tokenizer.sanitizers.config.SanitizerConfig
+ 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
+::: nominatim_db.data.place_info.PlaceInfo
+ options:
heading_level: 6
#### PlaceName - extended naming information
-::: nominatim.data.place_name.PlaceName
- rendering:
- show_source: no
+::: nominatim_db.data.place_name.PlaceName
+ 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:
+
+!!! example
+ ``` 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 meant 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
+[`src/nominatim_db/tokenizer/sanitizers`](https://github.com/osm-search/Nominatim/tree/master/src/nominatim_db/tokenizer/sanitizers).
-::: nominatim.tokenizer.token_analysis.base.AnalysisModule
- rendering:
- show_source: no
+
+## Custom token analysis module
+
+::: nominatim_db.tokenizer.token_analysis.base.AnalysisModule
+ options:
heading_level: 6
-::: nominatim.tokenizer.token_analysis.base.Analyzer
- rendering:
- show_source: no
+::: nominatim_db.tokenizer.token_analysis.base.Analyzer
+ 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.
+
projects / nominatim.git / blobdiff