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CREATE TEXT SEARCH DICTIONARY

Updated at: Mar 13, 2020 GMT+08:00

Function

CREATE TEXT SEARCH DICTIONARY creates a full-text retrieval dictionary. A dictionary is used to identify and process particular words during full-text retrieval.

Dictionaries are created by using predefined templates (defined in the PG_TS_TEMPLATE system catalog). Five types of dictionaries can be created, Simple, Ispell, Synonym, Thesaurus, and Snowball. Each type of dictionaries is used to handle different tasks.

Precautions

  • A user with the SYSADMIN permission can create a dictionary. Then, the user automatically becomes the owner of the dictionary.
  • A dictionary cannot be created in pg_temp mode.
  • After a dictionary is created or modified, any modification to the user-defined dictionary definition file will not affect the dictionary in the database. To make such modifications take effect in the dictionary in the database, run the ALTER statement to update the definition file of the dictionary.

Syntax

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CREATE TEXT SEARCH DICTIONARY name (
    TEMPLATE = template
    [, option = value [, ... ]]
);

Parameter Description

  • name

    Specifies the name of a dictionary to be created. (If you do not specify a schema name, the dictionary will be created in the current schema.)

    Value range: a string, which complies with the identifier naming convention. A value can contain a maximum of 63 characters.

  • template

    Specifies a template name.

    Valid value: templates (Simple, Synonym, Thesaurus, Ispell, and Snowball) defined in the PG_TS_TEMPLATE system catalog

  • option

    Specifies a parameter name. Each type of dictionaries has a template containing their custom parameters. Parameters function in a way irrelevant to their setting sequence.

    • Parameters for a Simple dictionary
      • STOPWORDS

        Specifies the name of a file listing stop words. The default file name extension is .stop. In the file, each line defines a stop word. Dictionaries will ignore blank lines and spaces in the file and convert stop-word phrases into lowercase.

      • ACCEPT

        Specifies whether to accept a non-stop word as recognized. The default value is true.

        If ACCEPT=true is set for a Simple dictionary, no token will be passed to subsequent dictionaries. In this case, you are advised to place the Simple dictionary at the end of the dictionary list. If ACCEPT=false is set, you are advised to place the Simple dictionary before at least one dictionary in the list.

      • FILEPATH

        Specifies the directory for storing dictionary files. The directory can be an OBS directory. The OBS directory format is obs://bucket_name/path accesskey=ak secretkey=sk region=rg. The default value is the directory where predefined dictionary files are located. If any of the FILEPATH and STOPWORDS parameters is specified, the other one must also be specified.

    • Parameters for a Synonym dictionary
      • SYNONYM

        Specifies the name of the definition file for a Synonym dictionary. The default file name extension is .syn.

        The file is a list of synonyms. Each line is in the format of token synonym, that is, token and its synonym separated by a space.

      • CASESENSITIVE

        Specifies whether tokens and their synonyms are case sensitive. The default value is false, indicating that tokens and synonyms in dictionary files will be converted into lowercase. If this parameter is set to true, they will not be converted into lowercase.

      • FILEPATH

        Specifies the directory for storing Synonym dictionary files. The directory can be an OBS directory. The OBS directory format is obs://bucket_name/path accesskey=ak secretkey=sk region=rg. The default value is the directory where predefined dictionary files are located.

    • Parameters for a Thesaurus dictionary
      • DICTFILE

        Specifies the name of a dictionary definition file. The default file name extension is .ths.

        The file is a list of synonyms. Each line is in the format of sample words : indexed words. The colon (:) is used as a separator between a phrase and its substitute word. If multiple sample words are matched, the TZ selects the longest one.

      • DICTIONARY

        Specifies the name of a subdictionary used for word normalization. This parameter is mandatory and only one subdictionary name can be specified. The specified subdictionary must exist. It is used to identify and normalize input text before phrase matching.

        If an input word cannot be recognized by the subdictionary, an error will be reported. In this case, remove the word or update the subdictionary to make the word recognizable. In addition, an asterisk (*) can be placed at the beginning of an indexed word to skip the application of a subdictionary on it, but all sample words must be recognizable by the subdictionary.

        If the sample words defined in the dictionary file contain stop words defined in the subdictionary, use question marks (?) to replace them. Assume that a and the are stop words defined in the subdictionary.
        ? one ? two : swsw

        a one the two and the one a two will be matched and output as swsw.

      • FILEPATH

        Specifies the directory for storing dictionary definition files. The directory can be an OBS directory. The OBS directory format is obs://bucket_name/path accesskey=ak secretkey=sk region=rg. The default value is the directory where predefined dictionary files are located.

    • Parameters for an Ispell dictionary
      • DICTFILE

        Specifies the name of a dictionary definition file. The default file name extension is .dict.

      • AFFFILE

        Specifies the name of an affix file. The default file name extension is .affix.

      • STOPWORDS

        Specifies the name of a file listing stop words. The default file name extension is .stop. The file content format is the same as that of the file for a Simple dictionary.

      • FILEPATH

        Specifies the directory for storing dictionary files. The directory can be an OBS directory. The OBS directory format is obs://bucket_name/path accesskey=ak secretkey=sk region=rg. The default value is the directory where predefined dictionary files are located.

    • Parameters for a Snowball dictionary
      • LANGUAGE

        Specifies the name of a language whose stemming algorithm will be used. According to spelling rules in the language, the algorithm normalizes the variants of an input word into a basic word or a stem.

      • STOPWORDS

        Specifies the name of a file listing stop words. The default file name extension is .stop. The file content format is the same as that of the file for a Simple dictionary.

      • FILEPATH

        Specifies the directory for storing dictionary definition files. The directory can be an OBS directory. The OBS directory format is obs://bucket_name/path accesskey=ak secretkey=sk region=rg. The default value is the directory where predefined dictionary files are located. If any of the FILEPATH and STOPWORDS parameters is specified, the other one must also be specified.

    The name of a dictionary definition file can contain only lowercase letters, digits, and underscores (_).

  • value

    Specifies a parameter value. If the value is not an identifier or a number, enclose it with single quotation marks (''). You can also enclose identifiers and numbers.

Examples

See examples in Configuration Examples.

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