Full-Text Module

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This XQuery Module extends the Full-Text features of BaseX: The index can be directly accessed, full-text results can be marked with additional elements, or the relevant parts can be extracted. Moreover, the score value, which is generated by the contains text expression, can be explicitly requested from items.

Conventions[edit]

All functions and errors in this module are assigned to the http://basex.org/modules/ft namespace, which is statically bound to the ft prefix.

Database Functions[edit]

ft:search[edit]

Signature 
ft:search(
  $db       as xs:string,
  $terms    as item()*,
  $options  as map(*)?    := map { }
) as text()*
Summary Returns all text nodes from the full-text index of the database $db that contain the specified $terms.
The options used for tokenizing the input and building the full-text will also be applied to the search terms. As an example, if the index terms have been stemmed, the search string will be stemmed as well.

The $options argument can be used to control full-text processing. The following options are supported (the introduction on Full-Text processing gives you equivalent expressions in the XQuery Full-Text notation):

  • mode: determine the mode how tokens are searched. Allowed values are any, any word, all, all words, and phrase. any is the default search mode.
  • wildcards: turn wildcard querying on or off. Allowed values are true and false. By default, wildcard querying is turned off.
  • fuzzy: turn fuzzy querying on or off. Allowed values are true and false. By default, fuzzy querying is turned off.
  • errors: control the maximum number of tolerated errors for fuzzy querying. By default, 0 is assigned (see Fuzzy Querying for more details).
  • ordered: indicate if all tokens must occur in the order in which they are specified. Allowed values are true and false. The default is false.
  • content: specify that the matched tokens need to occur at the beginning or end of a searched string, or need to cover the entire string. Allowed values are start, end, and entire. By default, the option is turned off.
  • scope: define the scope in which tokens must be located. The option has following sub options:
    • same: can be set to true or false. It specifies if tokens need to occur in the same or different units.
    • unit: can be sentence or paragraph. It specifies the unit for finding tokens.
  • window: set up a window in which all tokens must be located. By default, the option is turned off. It has following sub options:
    • size: specify the size of the window in terms of units.
    • unit: can be sentences, sentences or paragraphs. The default is words.
  • distance: specify the distance in which tokens must occur. By default, the option is turned off. It has following sub options:
    • min: specify the minimum distance in terms of units. The default is 0.
    • max: specify the maximum distance in terms of units. The default is ∞.
    • unit: can be words, sentences or paragraphs. The default is words.
Errors db:get: The addressed database does not exist or could not be opened.
db:no-index: the index is not available.
options: the fuzzy and wildcard option cannot be both specified.
Examples
  • ft:search("DB", "QUERY"): Return all text nodes of the database DB that contain the term QUERY.
  • Return all text nodes of the database DB that contain the numbers 2010 and 2020:
    ft:search("DB", ("2010", "2020"), map { 'mode': 'all' })
  • Return text nodes that contain the terms A and B in a distance of at most 5 words:
ft:search("db", ("A", "B"), map {
  "mode": "all words",
  "distance": map {
    "max": "5",
    "unit": "words"
  }
})
  • Iterate over three databases and return all elements containing terms similar to Hello World in the text nodes:
let $terms := "Hello Worlds"
let $fuzzy := true()
for $db in 1 to 3
let $dbname := 'DB' || $db
return ft:search($dbname, $terms, map { 'fuzzy': $fuzzy })/..

ft:tokens[edit]

Signature 
ft:tokens(
  $db      as xs:string,
  $prefix  as xs:string  := ()
) as element(value)*
Summary Returns all full-text tokens stored in the index of the database $db, along with their numbers of occurrences.
If $prefix is specified, the returned nodes will be refined to the strings starting with that prefix. The prefix will be tokenized according to the full-text used for creating the index.
Errors db:get: The addressed database does not exist or could not be opened.
db:no-index: the full-text index is not available.
Examples Returns the number of occurrences for a single, specific index entry: 
let $term := ft:tokenize($term)
return number(ft:tokens('db', $term)[. = $term]/@count)

General Functions[edit]

ft:contains[edit]

Signature 
ft:contains(
  $input    as item()*,
  $terms    as item()*,
  $options  as map(*)?  := map { }
) as xs:boolean
Summary Checks if the specified $input items contain the specified $terms.
The function does the same as the Full-Text expression contains text, but options can be specified more dynamically. The $options are the same as for ft:search, and the following ones exist:
  • case: determines how character case is processed. Allowed values are insensitive, sensitive, upper and lower. By default, search is case-insensitive.
  • diacritics: determines how diacritical characters are processed. Allowed values are insensitive and sensitive. By default, search is diacritical insensitive.
  • stemming: determines is tokens are stemmed. Allowed values are true and false. By default, stemming is turned off.
  • language: determines the language. This option is relevant for stemming tokens. All language codes are supported. The default language is en.
Errors options: specified options are conflicting.
Examples
  • Checks if jack or john occurs in the input string John Doe:
ft:contains("John Doe", ("jack", "john"), map { "mode": "any" })
  • Calls the function with stemming turned on and off:
(true(), false()) ! ft:contains("Häuser", "Haus", map { 'stemming': ., 'language':'de' })

ft:count[edit]

Signature 
ft:count(
  $nodes  as node()*
) as xs:integer
Summary Returns the number of occurrences of the search terms specified in a full-text expression.
Examples
  • ft:count(//*[text() contains text 'QUERY']) returns the xs:integer value 2 if a document contains two occurrences of the string "QUERY".

ft:score[edit]

Signature 
ft:score(
  $item  as item()*
) as xs:double*
Summary Returns the score values (0.0 - 1.0) that have been attached to the specified items. 0 is returned a value if no score was attached.
Examples
  • ft:score('a' contains text 'a') returns the xs:double value 1.

ft:tokenize[edit]

Signature 
ft:tokenize(
  $string   as xs:string?,
  $options  as map(*)?     := map { }
) as xs:string*
Summary Tokenizes the given $string, using the current default full-text options or the $options specified as second argument, and returns a sequence with the tokenized string. The following options are available:
  • case: determines how character case is processed. Allowed values are insensitive, sensitive, upper and lower. By default, search is case insensitive.
  • diacritics: determines how diacritical characters are processed. Allowed values are insensitive and sensitive. By default, search is diacritical insensitive.
  • stemming: determines is tokens are stemmed. Allowed values are true and false. By default, stemming is turned off.
  • language: determines the language. This option is relevant for stemming tokens. All language codes are supported. The default language is en.

The $options argument can be used to control full-text processing.

Examples
  • ft:tokenize("No Doubt") returns the two strings no and doubt.
  • ft:tokenize("École", map { 'diacritics': 'sensitive' }) returns the string école.
  • declare ft-option using stemming; ft:tokenize("GIFTS") returns a single string gift.

ft:normalize[edit]

Signature 
ft:normalize(
  $string   as xs:string?,
  $options  as map(*)?     := map { }
) as xs:string
Summary Normalizes the given $string, using the current default full-text options or the $options specified as second argument. The function accepts the same arguments as ft:tokenize; special characters and separators will be preserved.
Examples
  • ft:normalize("Häuser am Meer", map { 'case': 'sensitive' }) returns the string Hauser am Meer.

ft:thesaurus[edit]

Signature 
ft:thesaurus(
  $node     as node(),
  $term     as xs:string,
  $options  as map(*)?    := map { }
) as xs:string*
Summary Looks up a $term in a Thesaurus Structure supplied by $node. The following $options exist:
  • relationship: determines the relationship between terms
  • levels: determines the maximum number of levels to traverse
Examples Returns happy and lucky: 
ft:thesaurus(
  <thesaurus>
    <entry>
      <term>happy</term>
      <synonym>
        <term>lucky</term>
        <relationship>RT</relationship>
      </synonym>
    </entry>
  </thesaurus>,
  'happy'
)

Highlighting Functions[edit]

ft:mark[edit]

Signature 
ft:mark(
  $nodes  as node()*,
  $name   as xs:string  := ()
) as node()*
Summary Puts a marker element around the resulting $nodes of a full-text request.
The default name of the marker element is mark. An alternative name can be chosen via the optional $name argument.
Please note that:
  • The full-text expression that computes the token positions must be specified as argument of the ft:mark() function, as all position information is lost in subsequent processing steps. You may need to specify more than one full-text expression if you want to use the function in a FLWOR expression, as shown in Example 2.
  • The supplied node must be a Database Node. As shown in Example 3, update or transform can be utilized to convert a fragment to the required internal representation.
Examples Example 1: The following query returns <XML><mark>hello</mark> world</XML>, if one text node of the database DB has the value "hello world": 
ft:mark(db:get('DB')//*[text() contains text 'hello'])

Example 2: The following expression loops through the first ten full-text results and marks the results in a second expression: 

let $start := 1
let $end   := 10
let $term  := 'welcome'
let $test  := function($node) { $node/text() contains text { $term } }
for $ft in (db:get('DB')//*[$test(.)])[position() = $start to $end]
return ft:mark($ft[$test(.)])

Example 3: The following expression returns <xml>hello <b>word</b></xml>: 

copy $p := <xml>hello world</xml>
modify ()
return ft:mark($p[text() contains text 'word'], 'b')

ft:extract[edit]

Signature 
ft:extract(
  $nodes   as node()*,
  $name    as xs:string   := (),
  $length  as xs:integer  := ()
) as node()*
Summary Extracts and returns relevant parts of full-text results. It puts a marker element around the resulting $nodes of a full-text index request and chops irrelevant sections of the result.
The default element name of the marker element is mark. An alternative element name can be chosen via the optional $name argument.
The default length of the returned text is 150 characters. An alternative length can be specified via the optional $length argument. Note that the effective text length may differ from the specified text due to formatting and readibility issues.
For more details on this function, please have a look at ft:mark.
Examples
  • The following query may return <XML>...<b>hello</b>...<XML> if a text node of the database DB contains the string "hello world":
ft:extract(db:get('DB')//*[text() contains text 'hello'], 'b', 1)

Errors[edit]

Code Description
options Both wildcards and fuzzy search have been specified as search options.

Changelog[edit]

Version 9.6
Version 9.1
Version 9.0
  • Updated: error codes updated; errors now use the module namespace
Version 8.0
Version 7.8
Version 7.7
  • Updated: the functions no longer accept Database Nodes as reference. Instead, the name of a database must now be specified.
Version 7.2
  • Updated: ft:search (second argument generalized, third parameter added)
Version 7.1
Retrieved from "https://old.docs.basex.org/index.php?title=Full-Text_Module&oldid=16821"