how tokenizers are expected to work and the public API that needs to be
implemented when creating a new tokenizer. For information on how to configure
a specific tokenizer for a database see the
-[tokenizer chapter in the administration guide](../admin/Tokenizers.md).
+[tokenizer chapter in the Customization Guide](../customize/Tokenizers.md).
## Generic Architecture
the specific place. This list is later needed in the PL/pgSQL part where the
indexer needs to add the token IDs to the appropriate search tables. To be
able to communicate the list between the Python part and the pl/pgSQL trigger,
-the placex table contains a special JSONB column `token_info` which is there
+the `placex` table contains a special JSONB column `token_info` which is there
for the exclusive use of the tokenizer.
The Python part of the tokenizer returns a structured information about the
### Querying
-The tokenizer is responsible for the initial parsing of the query. It needs
-to split the query into appropriate words and terms and match them against
-the saved tokens in the database. It then returns the list of possibly matching
-tokens and the list of possible splits to the query parser. The parser uses
-this information to compute all possible interpretations of the query and
-rank them accordingly.
+At query time, Nominatim builds up multiple _interpretations_ of the search
+query. Each of these interpretations is tried against the database in order
+of the likelihood with which they match to the search query. The first
+interpretation that yields results wins.
+
+The interpretations are encapsulated in the `SearchDescription` class. An
+instance of this class is created by applying a sequence of
+_search tokens_ to an initially empty SearchDescription. It is the
+responsibility of the tokenizer to parse the search query and derive all
+possible sequences of search tokens. To that end the tokenizer needs to parse
+the search query and look up matching words in its own data structures.
## Tokenizer API
### Directory Structure
-Nominatim expects two files for a tokenizer:
-
-* `nominiatim/tokenizer/<NAME>_tokenizer.py` containing the Python part of the
- implementation
-* `lib-php/tokenizer/<NAME>_tokenizer.php` with the PHP part of the
- implementation
-
-where `<NAME>` is a unique name for the tokenizer consisting of only lower-case
+Nominatim expects a single file `src/nominatim_db/tokenizer/<NAME>_tokenizer.py`
+containing the Python part of the implementation.
+`<NAME>` is a unique name for the tokenizer consisting of only lower-case
letters, digits and underscore. A tokenizer also needs to install some SQL
functions. By convention, these should be placed in `lib-sql/tokenizer`.
If the tokenizer has a default configuration file, this should be saved in
the `settings/<NAME>_tokenizer.<SUFFIX>`.
-### Configuration and Persistance
+### Configuration and Persistence
Tokenizers may define custom settings for their configuration. All settings
must be prefixed with `NOMINATIM_TOKENIZER_`. Settings may be transient or
### Python Tokenizer Class
-All tokenizers must inherit from `nominatim.tokenizer.base.AbstractTokenizer`
+All tokenizers must inherit from `nominatim_db.tokenizer.base.AbstractTokenizer`
and implement the abstract functions defined there.
-::: nominatim.tokenizer.base.AbstractTokenizer
- rendering:
- heading_level: 4
+::: nominatim_db.tokenizer.base.AbstractTokenizer
+ options:
+ heading_level: 6
### Python Analyzer Class
-::: nominatim.tokenizer.base.AbstractAnalyzer
- rendering:
- heading_level: 4
+::: nominatim_db.tokenizer.base.AbstractAnalyzer
+ options:
+ heading_level: 6
### PL/pgSQL Functions
house numbers.
```sql
-FUNCTION token_addr_street_match_tokens(info JSONB) RETURNS INTEGER[]
+FUNCTION token_is_street_address(info JSONB) RETURNS BOOLEAN
```
-Return the match token IDs by which to search a matching street from the
-`addr:street` tag. These IDs will be matched against the IDs supplied by
-`token_get_name_match_tokens`. Must be NULL when the place has no `addr:street`
-tag.
+Return true if this is an object that should be parented against a street.
+Only relevant for objects with address rank 30.
```sql
-FUNCTION token_addr_place_match_tokens(info JSONB) RETURNS INTEGER[]
+FUNCTION token_has_addr_street(info JSONB) RETURNS BOOLEAN
```
-Return the match token IDs by which to search a matching place from the
-`addr:place` tag. These IDs will be matched against the IDs supplied by
-`token_get_name_match_tokens`. Must be NULL when the place has no `addr:place`
-tag.
-
-```sql
-FUNCTION token_addr_place_search_tokens(info JSONB) RETURNS INTEGER[]
-```
+Return true if there are street names to match against for finding the
+parent of the object.
-Return the search token IDs extracted from the `addr:place` tag. These tokens
-are used for searches by address when no matching place can be found in the
-database. Must be NULL when the place has no `addr:place` tag.
```sql
-CREATE TYPE token_addresstoken AS (
- key TEXT,
- match_tokens INT[],
- search_tokens INT[]
-);
-
-FUNCTION token_get_address_tokens(info JSONB) RETURNS SETOF token_addresstoken
+FUNCTION token_has_addr_place(info JSONB) RETURNS BOOLEAN
```
-Return the match and search token IDs for explicit `addr:*` tags for the place
-other than `addr:street` and `addr:place`. For each address item there are
-three pieces of information returned:
-
- * _key_ contains the type of address item (city, county, etc.). This is the
- key handed in with the `address` dictionary.
- * *match_tokens* is the list of token IDs used to find the corresponding
- place object for the address part. The list is matched against the IDs
- from `token_get_name_match_tokens`.
- * *search_tokens* is the list of token IDs under which to search the address
- item. It is used when no corresponding place object was found.
+Return true if there are place names to match against for finding the
+parent of the object.
```sql
-FUNCTION token_normalized_postcode(postcode TEXT) RETURNS TEXT
+FUNCTION token_matches_street(info JSONB, street_tokens INTEGER[]) RETURNS BOOLEAN
```
-Return the normalized version of the given postcode. This function must return
-the same value as the Python function `AbstractAnalyzer->normalize_postcode()`.
+Check if the given tokens (previously saved from `token_get_name_match_tokens()`)
+match against the `addr:street` tag name. Must return either NULL or FALSE
+when the place has no `addr:street` tag.
```sql
-FUNCTION token_strip_info(info JSONB) RETURNS JSONB
+FUNCTION token_matches_place(info JSONB, place_tokens INTEGER[]) RETURNS BOOLEAN
```
-Return the part of the `token_info` field that should be stored in the database
-permanently. The indexer calls this function when all processing is done and
-replaces the content of the `token_info` column with the returned value before
-the trigger stores the information in the database. May return NULL if no
-information should be stored permanently.
-
-### PHP Tokenizer class
-
-The PHP tokenizer class is instantiated once per request and responsible for
-analyzing the incoming query. Multiple requests may be in flight in
-parallel.
+Check if the given tokens (previously saved from `token_get_name_match_tokens()`)
+match against the `addr:place` tag name. Must return either NULL or FALSE
+when the place has no `addr:place` tag.
-The class is expected to be found under the
-name of `\Nominatim\Tokenizer`. To find the class the PHP code includes the file
-`tokenizer/tokenizer.php` in the project directory. This file must be created
-when the tokenizer is first set up on import. The file should initialize any
-configuration variables by setting PHP constants and then require the file
-with the actual implementation of the tokenizer.
-The tokenizer class must implement the following functions:
-
-```php
-public function __construct(object &$oDB)
+```sql
+FUNCTION token_addr_place_search_tokens(info JSONB) RETURNS INTEGER[]
```
-The constructor of the class receives a database connection that can be used
-to query persistent data in the database.
+Return the search token IDs extracted from the `addr:place` tag. These tokens
+are used for searches by address when no matching place can be found in the
+database. Must be NULL when the place has no `addr:place` tag.
-```php
-public function checkStatus()
+```sql
+FUNCTION token_get_address_keys(info JSONB) RETURNS SETOF TEXT
```
-Check that the tokenizer can access its persistent data structures. If there
-is an issue, throw an `\Exception`.
+Return the set of keys for which address information is provided. This
+should correspond to the list of (relevant) `addr:*` tags with the `addr:`
+prefix removed or the keys used in the `address` dictionary of the place info.
-```php
-public function normalizeString(string $sTerm) : string
+```sql
+FUNCTION token_get_address_search_tokens(info JSONB, key TEXT) RETURNS INTEGER[]
```
-Normalize string to a form to be used for comparisons when reordering results.
-Nominatim reweighs results how well the final display string matches the actual
-query. Before comparing result and query, names and query are normalised against
-this function. The tokenizer can thus remove all properties that should not be
-taken into account for reweighing, e.g. special characters or case.
+Return the array of search tokens for the given address part. `key` can be
+expected to be one of those returned with `token_get_address_keys()`. The
+search tokens are added to the address search vector of the place, when no
+corresponding OSM object could be found for the given address part from which
+to copy the name information.
-```php
-public function tokensForSpecialTerm(string $sTerm) : array
+```sql
+FUNCTION token_matches_address(info JSONB, key TEXT, tokens INTEGER[])
```
-Return the list of special term tokens that match the given term.
+Check if the given tokens match against the address part `key`.
+
+__Warning:__ the tokens that are handed in are the lists previously saved
+from `token_get_name_search_tokens()`, _not_ from the match token list. This
+is an historical oddity which will be fixed at some point in the future.
+Currently, tokenizers are encouraged to make sure that matching works against
+both the search token list and the match token list.
-```php
-public function extractTokensFromPhrases(array &$aPhrases) : TokenList
+```sql
+FUNCTION token_get_postcode(info JSONB) RETURNS TEXT
```
-Parse the given phrases, splitting them into word lists and retrieve the
-matching tokens.
+Return the postcode for the object, if any exists. The postcode must be in
+the form that should also be presented to the end-user.
-For each phrase in the list of phrases, the function must analyse the phrase
-string and then call `setWordSets()` to communicate the result of the analysis.
-A word set is a list of strings, where each string refers to a search token.
-A phrase may have multiple interpretations. Therefore a list of word sets is
-usually attached to the phrase. The search tokens themselves are returned
-by the function in an associative array, where the key corresponds to the
-strings given in the word sets. The value is a list of search tokens. Thus
-a single string in the list of word sets may refer to multiple search tokens.
+```sql
+FUNCTION token_strip_info(info JSONB) RETURNS JSONB
+```
+Return the part of the `token_info` field that should be stored in the database
+permanently. The indexer calls this function when all processing is done and
+replaces the content of the `token_info` column with the returned value before
+the trigger stores the information in the database. May return NULL if no
+information should be stored permanently.
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