normalize names and queries. It also offers configurable decomposition and
abbreviation handling.
+To enable the tokenizer add the following line to your project configuration:
+
+```
+NOMINATIM_TOKENIZER=icu
+```
+
### How it works
-On import the tokenizer processes names in the following four stages:
+On import the tokenizer processes names in the following three stages:
-1. The **Normalization** part removes all non-relevant information from the
- input.
-2. Incoming names are now converted to **full names**. This process is currently
- hard coded and mostly serves to handle name tags from OSM that contain
- multiple names (e.g. [Biel/Bienne](https://www.openstreetmap.org/node/240097197)).
-3. Next the tokenizer creates **variants** from the full names. These variants
- cover decomposition and abbreviation handling. Variants are saved to the
- database, so that it is not necessary to create the variants for a search
- query.
-4. The final **Tokenization** step converts the names to a simple ASCII form,
- potentially removing further spelling variants for better matching.
+1. During the **Sanitizer step** incoming names are cleaned up and converted to
+ **full names**. This step can be used to regularize spelling, split multi-name
+ tags into their parts and tag names with additional attributes. See the
+ [Sanitizers section](#sanitizers) below for available cleaning routines.
+2. The **Normalization** part removes all information from the full names
+ that are not relevant for search.
+3. The **Token analysis** step takes the normalized full names and creates
+ all transliterated variants under which the name should be searchable.
+ See the [Token analysis](#token-analysis) section below for more
+ information.
-At query time only stage 1) and 4) are used. The query is normalized and
-tokenized and the resulting string used for searching in the database.
+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.
### Configuration
transliteration:
- !include /etc/nominatim/icu-rules/extended-unicode-to-asccii.yaml
- ":: Ascii ()"
-variants:
- - language: de
- words:
- - ~haus => haus
- - ~strasse -> str
- - language: en
- words:
- - road -> rd
- - bridge -> bdge,br,brdg,bri,brg
+sanitizers:
+ - step: split-name-list
+token-analysis:
+ - analyzer: generic
+ variants:
+ - !include icu-rules/variants-ca.yaml
+ - words:
+ - road -> rd
+ - bridge -> bdge,br,brdg,bri,brg
```
-The configuration file contains three sections:
-`normalization`, `transliteration`, `variants`.
+The configuration file contains four sections:
+`normalization`, `transliteration`, `sanitizers` and `token-analysis`.
+
+#### Normalization and Transliteration
+
+The normalization and transliteration sections each define a set of
+ICU rules that are applied to the names.
+
+The **normalisation** rules are applied after sanitation. They should remove
+any information that is not relevant for search at all. Usual rules to be
+applied here are: lower-casing, removing of special characters, cleanup of
+spaces.
-The normalization and transliteration sections each must contain a list of
+The **transliteration** rules are applied at the end of the tokenization
+process to transfer the name into an ASCII representation. Transliteration can
+be useful to allow for further fuzzy matching, especially between different
+scripts.
+
+Each section must contain a list of
[ICU transformation rules](https://unicode-org.github.io/icu/userguide/transforms/general/rules.html).
The rules are applied in the order in which they appear in the file.
You can also include additional rules from external yaml file using the
YAML syntax. You should therefore always enclose the ICU rules in
double-quotes.
+#### Sanitizers
+
+The sanitizers section defines an ordered list of functions that are applied
+to the name and address tags before they are further processed by the tokenizer.
+They allows to clean up the tagging and bring it to a standardized form more
+suitable for building the search index.
+
+!!! hint
+ Sanitizers only have an effect on how the search index is built. They
+ do not change the information about each place that is saved in the
+ database. In particular, they have no influence on how the results are
+ displayed. The returned results always show the original information as
+ stored in the OpenStreetMap database.
+
+Each entry contains information of a sanitizer to be applied. It has a
+mandatory parameter `step` which gives the name of the sanitizer. Depending
+on the type, it may have additional parameters to configure its operation.
+
+The order of the list matters. The sanitizers are applied exactly in the order
+that is configured. Each sanitizer works on the results of the previous one.
+
+The following is a list of sanitizers that are shipped with Nominatim.
+
+##### split-name-list
+
+::: nominatim.tokenizer.sanitizers.split_name_list
+ selection:
+ members: False
+ rendering:
+ heading_level: 6
+
+##### strip-brace-terms
+
+::: nominatim.tokenizer.sanitizers.strip_brace_terms
+ selection:
+ members: False
+ rendering:
+ heading_level: 6
+
+##### tag-analyzer-by-language
+
+::: nominatim.tokenizer.sanitizers.tag_analyzer_by_language
+ selection:
+ members: False
+ rendering:
+ heading_level: 6
+
+
+
+#### Token Analysis
+
+Token analyzers take a full name and transform it into one or more normalized
+form that are then saved in the search index. In its simplest form, the
+analyzer only applies the transliteration rules. More complex analyzers
+create additional spelling variants of a name. This is useful to handle
+decomposition and abbreviation.
+
+The ICU tokenizer may use different analyzers for different names. To select
+the analyzer to be used, the name must be tagged with the `analyzer` attribute
+by a sanitizer (see for example the
+[tag-analyzer-by-language sanitizer](#tag-analyzer-by-language)).
+
+The token-analysis section contains the list of configured analyzers. Each
+analyzer must have an `id` parameter that uniquely identifies the analyzer.
+The only exception is the default analyzer that is used when no special
+analyzer was selected.
+
+Different analyzer implementations may exist. To select the implementation,
+the `analyzer` parameter must be set. Currently there is only one implementation
+`generic` which is described in the following.
+
+##### Generic token analyzer
+
+The generic analyzer is able to create variants from a list of given
+abbreviation and decomposition replacements. It takes one optional parameter
+`variants` which lists the replacements to apply. If the section is
+omitted, then the generic analyzer becomes a simple analyzer that only
+applies the transliteration.
+
The variants section defines lists of replacements which create alternative
spellings of a name. To create the variants, a name is scanned from left to
right and the longest matching replacement is applied until the end of the
words in the configuration because then it is possible to change the
rules for normalization later without having to adapt the variant rules.
-#### Decomposition
+###### Decomposition
In its standard form, only full words match against the source. There
is a special notation to match the prefix and suffix of a word:
simply changes "hauptstrasse" to "hauptstr" and "rote strasse" to "rote str".
-#### Initial and final terms
+###### Initial and final terms
It is also possible to restrict replacements to the beginning and end of a
name:
``` yaml
-- ^south => n # matches only at the beginning of the name
+- ^south => s # matches only at the beginning of the name
- road$ => rd # matches only at the end of the name
```
So the first example would trigger a replacement for "south 45th street" but
not for "the south beach restaurant".
-#### Replacements vs. variants
+###### Replacements vs. variants
The replacement syntax `source => target` works as a pure replacement. It changes
the name instead of creating a variant. To create an additional version, you'd
The simple arrow causes an additional variant to be added. Note that
decomposition has an effect here on the source as well. So a rule
-```yaml
-- ~strasse => str
+``` yaml
+- "~strasse -> str"
```
means that for a word like `hauptstrasse` four variants are created:
projects / nominatim.git / blobdiff