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add documentation for new configuration of ICU tokenizer

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Sarah Hoffmann 2021-10-07 11:55:53 +02:00
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153
docs/admin/Tokenizers.md
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@ -60,22 +60,23 @@ 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
@ -93,21 +94,36 @@ normalization:
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`.
The normalization and transliteration sections each must contain a list of
#### 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 **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
@ -119,6 +135,85 @@ and may again include other files.
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
@ -144,7 +239,7 @@ term.
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:
@ -171,7 +266,7 @@ To avoid automatic decomposition, use the '|' notation:
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:
@ -184,7 +279,7 @@ 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

10
nominatim/tokenizer/sanitizers/split_name_list.py
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@ -1,5 +1,9 @@
"""
Name processor that splits name values with multiple values into their components.
Sanitizer that splits lists of names into their components.
Arguments:
delimiters: Define the set of characters to be used for
splitting the list. (default: `,;`)
"""
import re
@ -7,9 +11,7 @@ from nominatim.errors import UsageError
def create(func):
""" Create a name processing function that splits name values with
multiple values into their components. The optional parameter
'delimiters' can be used to define the characters that should be used
for splitting. The default is ',;'.
multiple values into their components.
"""
delimiter_set = set(func.get('delimiters', ',;'))
if not delimiter_set:

7
nominatim/tokenizer/sanitizers/strip_brace_terms.py
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@ -1,11 +1,12 @@
"""
Sanitizer handling names with addendums in braces.
This sanitizer creates additional name variants for names that have
addendums in brackets (e.g. "Halle (Saale)"). The additional variant contains
only the main name part with the bracket part removed.
"""
def create(_):
""" Create a name processing function that creates additional name variants
when a name has an addendum in brackets (e.g. "Halle (Saale)"). The
additional variant only contains the main name without the bracket part.
for bracket addendums.
"""
def _process(obj):
""" Add variants for names that have a bracket extension.

45
nominatim/tokenizer/sanitizers/tag_analyzer_by_language.py
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@ -1,5 +1,28 @@
"""
Name processor for tagging the langauge of the name
This sanitizer sets the `analyzer` property depending on the
language of the tag. The language is taken from the suffix of the name.
If a name already has an analyzer tagged, then this is kept.
Arguments:
filter-kind: Restrict the names the sanitizer should be applied to
to the given tags. The parameter expects a list of
regular expressions which are matched against `kind`.
Note that a match against the full string is expected.
whitelist: Restrict the set of languages that should be tagged.
Expects a list of acceptable suffixes. When unset,
all 2- and 3-letter lower-case codes are accepted.
use-defaults: Configure what happens when the name has no suffix.
When set to 'all', a variant is created for
each of the default languages in the country
the feature is in. When set to 'mono', a variant is
only created, when exactly one language is spoken
in the country. The default is to do nothing with
the default languages of a country.
mode: Define how the variants are created and may be 'replace' or
'append'. When set to 'append' the original name (without
any analyzer tagged) is retained. (default: replace)
"""
import re
@ -75,24 +98,6 @@ class _AnalyzerByLanguage:
def create(config):
""" Create a function that sets the analyzer property depending on the
language of the tag. The language is taken from the suffix.
To restrict the set of languages that should be tagged, use
'whitelist'. A list of acceptable suffixes. When unset, all 2- and
3-letter codes are accepted.
'use-defaults' configures what happens when the name has no suffix
with a language tag. When set to 'all', a variant is created for
each on the spoken languages in the country the feature is in. When
set to 'mono', a variant is created, when only one language is spoken
in the country. The default is, to do nothing with the default languages
of a country.
'mode' hay be 'replace' (the default) or 'append' and configures if
the original name (without any analyzer tagged) is retained.
With 'filter-kind' the set of names the sanitizer should be applied
to can be retricted to the given patterns of 'kind'. It expects a
list of regular expression to be matched against 'kind'.
language of the tag.
"""
return _AnalyzerByLanguage(config)