This topic describes the types of tokens the Greenplum Database text search parser produces from raw text.

    Text search parsers are responsible for splitting raw document text into tokens and identifying each token’s type, where the set of possible types is defined by the parser itself. Note that a parser does not modify the text at all — it simply identifies plausible word boundaries. Because of this limited scope, there is less need for application-specific custom parsers than there is for custom dictionaries. At present Greenplum Database provides just one built-in parser, which has been found to be useful for a wide range of applications.

    The built-in parser is named pg_catalog.default. It recognizes 23 token types, shown in the following table.

    Alias Description Example
    asciiword Word, all ASCII letters elephant
    word Word, all letters mañana
    numword Word, letters and digits beta1
    asciihword Hyphenated word, all ASCII up-to-date
    hword Hyphenated word, all letters lógico-matemática
    numhword Hyphenated word, letters and digits postgresql-beta1
    hword_asciipart Hyphenated word part, all ASCII postgresql in the context postgresql-beta1
    hword_part Hyphenated word part, all letters lógico or matemática in the context lógico-matemática
    hword_numpart Hyphenated word part, letters and digits beta1 in the context postgresql-beta1
    email Email address foo@example.com
    protocol Protocol head http://
    url URL example.com/stuff/index.html
    host Host example.com
    url_path URL path /stuff/index.html, in the context of a URL
    file File or path name /usr/local/foo.txt, if not within a URL
    sfloat Scientific notation -1.234e56
    float Decimal notation -1.234
    int Signed integer -1234
    uint Unsigned integer 1234
    version Version number 8.3.0
    tag XML tag <a href=”dictionaries.html”>
    entity XML entity &
    blank Space symbols (any whitespace or punctuation not otherwise recognized)

    Note

    The parser’s notion of a “letter” is determined by the database’s locale setting, specifically lc_ctype. Words containing only the basic ASCII letters are reported as a separate token type, since it is sometimes useful to distinguish them. In most European languages, token types word and asciiword should be treated alike.

    email does not support all valid email characters as defined by RFC 5322. Specifically, the only non-alphanumeric characters supported for email user names are period, dash, and underscore.

    It is possible for the parser to produce overlapping tokens from the same piece of text. As an example, a hyphenated word will be reported both as the entire word and as each component:

    1. SELECT alias, description, token FROM ts_debug('foo-bar-beta1');
2. alias      |               description                |     token
3. -----------------+------------------------------------------+---------------
4. numhword        | Hyphenated word, letters and digits      | foo-bar-beta1
5. hword_asciipart | Hyphenated word part, all ASCII          | foo
6. blank           | Space symbols                            | -
7. hword_asciipart | Hyphenated word part, all ASCII          | bar
8. blank           | Space symbols                            | -
9. hword_numpart   | Hyphenated word part, letters and digits | beta1

    This behavior is desirable since it allows searches to work for both the whole compound word and for components. Here is another instructive example:

    1. SELECT alias, description, token FROM ts_debug('http://example.com/stuff/index.html');
2. alias   |  description  |            token
3. ----------+---------------+------------------------------
4. protocol | Protocol head | http://
5. url      | URL           | example.com/stuff/index.html
6. host     | Host          | example.com
7. url_path | URL path      | /stuff/index.html

    Parent topic: Using Full Text Search