Merge pull request #2974 from bloom256/main-tag-in-reverse-lookup

[nominatim.git] / docs / develop / Tokenizers.md

diff --git a/docs/develop/Tokenizers.md b/docs/develop/Tokenizers.md
index fe9b02aded8b08fa63e3537fb89bc1766fad2af8..273e65e2126381a65b2d27361d71269c2ec439c5 100644 (file)
--- a/docs/develop/Tokenizers.md
+++ b/docs/develop/Tokenizers.md
@@ -6,7 +6,7 @@ tokenizers that use different strategies for normalisation. This page describes
 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
 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
 
 
 ## Generic Architecture
 


@@ -50,7 +50,7 @@ tokenizer's internal token lists and creating a list of all token IDs for
 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 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
 for the exclusive use of the tokenizer.
 
 The Python part of the tokenizer returns a structured information about the


@@ -67,12 +67,17 @@ consequently not create any special indexes on it.
 
 ### Querying
 
 
 ### 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
 
 
 ## Tokenizer API
 


@@ -88,7 +93,7 @@ for a custom tokenizer implementation.
 
 Nominatim expects two files for a tokenizer:
 
 
 Nominatim expects two files for a tokenizer:
 

-* `nominiatim/tokenizer/<NAME>_tokenizer.py` containing the Python part of the
+* `nominatim/tokenizer/<NAME>_tokenizer.py` containing the Python part of the

   implementation
 * `lib-php/tokenizer/<NAME>_tokenizer.php` with the PHP part of the
   implementation
   implementation
 * `lib-php/tokenizer/<NAME>_tokenizer.php` with the PHP part of the
   implementation


@@ -100,7 +105,7 @@ 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>`.
 
 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
 
 Tokenizers may define custom settings for their configuration. All settings
 must be prefixed with `NOMINATIM_TOKENIZER_`. Settings may be transient or


@@ -185,22 +190,21 @@ be listed with a semicolon as delimiter. Must be NULL when the place has no
 house numbers.
 
 ```sql
 house numbers.
 
 ```sql

-FUNCTION token_addr_street_match_tokens(info JSONB) RETURNS INTEGER[]
+FUNCTION token_matches_street(info JSONB, street_tokens INTEGER[]) 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.
+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
 
 ```sql

-FUNCTION token_addr_place_match_tokens(info JSONB) RETURNS INTEGER[]
+FUNCTION token_matches_place(info JSONB, place_tokens INTEGER[]) 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.
+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.
+

 
 ```sql
 FUNCTION token_addr_place_search_tokens(info JSONB) RETURNS INTEGER[]
 
 ```sql
 FUNCTION token_addr_place_search_tokens(info JSONB) RETURNS INTEGER[]


@@ -211,33 +215,41 @@ 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
 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_keys(info JSONB) RETURNS SETOF TEXT
+```
+
+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.

 
 

-FUNCTION token_get_address_tokens(info JSONB) RETURNS SETOF token_addresstoken
+```sql
+FUNCTION token_get_address_search_tokens(info JSONB, key TEXT) RETURNS INTEGER[]

 ```
 
 ```
 

-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:
+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.
+
+```sql
+FUNCTION token_matches_address(info JSONB, key TEXT, tokens INTEGER[])
+```

 
 

- * _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.
+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.

 
 ```sql
 
 ```sql

-FUNCTION token_normalized_postcode(postcode TEXT) RETURNS TEXT
+FUNCTION token_get_postcode(info JSONB) RETURNS TEXT

 ```
 
 ```
 

-Return the normalized version of the given postcode. This function must return
-the same value as the Python function `AbstractAnalyzer->normalize_postcode()`.
+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.

 
 ```sql
 FUNCTION token_strip_info(info JSONB) RETURNS JSONB
 
 ```sql
 FUNCTION token_strip_info(info JSONB) RETURNS JSONB


@@ -248,3 +260,73 @@ 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.
 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.
+
+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)
+```
+
+The constructor of the class receives a database connection that can be used
+to query persistent data in the database.
+
+```php
+public function checkStatus()
+```
+
+Check that the tokenizer can access its persistent data structures. If there
+is an issue, throw an `\Exception`.
+
+```php
+public function normalizeString(string $sTerm) : string
+```
+
+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.
+
+```php
+public function tokensForSpecialTerm(string $sTerm) : array
+```
+
+Return the list of special term tokens that match the given term.
+
+```php
+public function extractTokensFromPhrases(array &$aPhrases) : TokenList
+```
+
+Parse the given phrases, splitting them into word lists and retrieve the
+matching tokens.
+
+The phrase array may take on two forms. In unstructured searches (using `q=`
+parameter) the search query is split at the commas and the elements are
+put into a sorted list. For structured searches the phrase array is an
+associative array where the key designates the type of the term (street, city,
+county etc.) The tokenizer may ignore the phrase type at this stage in parsing.
+Matching phrase type and appropriate search token type will be done later
+when the SearchDescription is built.
+
+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.
+