X-Git-Url: https://git.openstreetmap.org./nominatim.git/blobdiff_plain/78d11fe62830fac30d7241d05cf0c2b74dfeeb00..f3c4196c758a7720aefc26a7043bf1c6553028e2:/docs/develop/Tokenizers.md?ds=sidebyside

diff --git a/docs/develop/Tokenizers.md b/docs/develop/Tokenizers.md
index fe9b02ad..529315e4 100644
--- a/docs/develop/Tokenizers.md
+++ b/docs/develop/Tokenizers.md
@@ -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 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
@@ -67,12 +67,17 @@ consequently not create any special indexes on it.
 
 ### 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
 
@@ -248,3 +253,73 @@ 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.
+
+### 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.
+