Builtin SPARQL functions

Besides the functions built in the SPARQL 1.1 syntax, type casts and functional properties, Tracker supports a number of SPARQL functions. Some of these functions have correspondences in XPath.

String functions

`fn:lower-case`

fn:lower-case (?string)

Converts a string to lowercase, equivalent to LCASE.

`fn:upper-case`

fn:upper-case (?string)

Converts a string to uppercase, equivalent to UCASE.

`fn:contains`

fn:contains (?haystack, ?needle)

Returns a boolean indicating whether ?needle is found in ?haystack. Equivalent to CONTAINS.

`fn:starts-with`

fn:starts-with (?string, ?prefix)

Returns a boolean indicating whether ?string starts with ?prefix. Equivalent to STRSTARTS.

`fn:ends-with`

fn:ends-with (?string, ?suffix)

Returns a boolean indicating whether ?string ends with ?suffix. Equivalent to STRENDS.

`fn:substring`

fn:substring (?string, ?startLoc)
fn:substring (?string, ?startLoc, ?endLoc)

Returns a substring delimited by the integer ?startLoc and ?endLoc arguments. If ?endLoc is omitted, the end of the string is used.

`fn:concat`

fn:concat (?string1, ?string2, ..., ?stringN)

Takes a variable number of arguments and returns a string concatenation of all its returned values. Equivalent to CONCAT.

`fn:string-join`

fn:string-join ((?string1, ?string2, ...), ?separator)

Takes a variable number of arguments and returns a string concatenation using ?separator to join all elements.

`fn:replace`

fn:replace (?string, ?regex, ?replacement)
fn:replace (?string, ?regex, ?replacement, ?flags)

Performs string replacement on ?string. All matches of ?regex are replaced by ?replacement in the returned string. This function is similar to REPLACE.

The ?flags argument is optional, a case search is performed if not provided.

If ?flags contains the character “s”, a dot metacharacter (“.”) in ?regex matches all characters, including newlines. Without it, newlines are excluded.

If ?flags contains the character “m”, the “start of line” (^) and “end of line” ($) constructs match immediately following or immediately before any newline in the string. If not set these constructs will respectively match the start and end of the full string.

If ?flags contains the character “i”, search is caseless.

If ?flags contains the character “x”, ?regex is interpreted to be an extended regular expression.

`tracker:case-fold`

tracker:case-fold (?string)

Converts a string into a form that is independent of case.

`tracker:title-order`

tracker:title-order (?string)

Manipulates a string to remove leading articles for sorting purposes, e.g. “Wall, The”. Best used in ORDER BY clauses.

`tracker:ascii-lower-case`

tracker:ascii-lower-case (?string)

Converts an ASCII string to lowercase, equivalent to LCASE.

`tracker:normalize`

tracker:normalize (?string, ?option)

Normalizes ?string. The ?option string must be one of nfc, nfd, nfkc or nfkd.

`tracker:unaccent`

tracker:unaccent (?string)

Removes accents from a string.

`tracker:coalesce`

tracker:coalesce (?value1, ?value2, ..., ?valueN)

Picks the first non-null value. Equivalent to COALESCE.

`tracker:strip-punctuation`

tracker:strip-punctuation (?string)

Removes any Unicode character which has the General Category value of P (Punctuation) from the string.

DateTime functions

`fn:year-from-dateTime`

fn:year-from-dateTime (?date)

Returns the year from a xsd:date type, a xsd:dateTime type, or a ISO8601 date string. This function is equivalent to YEAR.

`fn:month-from-dateTime`

fn:month-from-dateTime (?date)

Returns the month from a xsd:date type, a xsd:dateTime type, or a ISO8601 date string. This function is equivalent to MONTH.

`fn:day-from-dateTime`

fn:day-from-dateTime (?date)

Returns the day from a xsd:date type, a xsd:dateTime type, or a ISO8601 date string. This function is equivalent to DAY.

`fn:hours-from-dateTime`

fn:hours-from-dateTime (?date)

Returns the hours from a xsd:dateTime type or a ISO8601 datetime string. This function is equivalent to HOURS.

`fn:minutes-from-dateTime`

fn:minutes-from-dateTime (?date)

Returns the minutes from a xsd:dateTime type or a ISO8601 datetime string. This function is equivalent to MINUTES.

`fn:seconds-from-dateTime`

fn:seconds-from-dateTime (?date)

Returns the seconds from a xsd:dateTime type or a ISO8601 datetime string. This function is equivalent to SECONDS.

`fn:timezone-from-dateTime`

fn:timezone-from-dateTime (?date)

Returns the timezone offset in minutes. This function is similar, but not equivalent to TIMEZONE or TZ.

Full-text search functions

`fts:rank`

fts:rank (?match)

Returns the rank of a full-text search match. Must be used in conjunction with fts:match.

`fts:offsets`

fts:offsets (?match)

Returns a string describing the offsets of a full-text search match. Must be used in conjunction with fts:match. The returned string has the format:

prefix:property:offset prefix:property:offset prefix:property:offset

`fts:snippet`

fts:snippet (?match)
fts:snippet (?match, ?delimStart, ?delimEnd)
fts:snippet (?match, ?delimStart, ?delimEnd, ?ellipsis)
fts:snippet (?match, ?delimStart, ?delimEnd, ?ellipsis, ?numTokens)

Returns a snippet string in accordance to the full-text search string. Must be used in conjunction with fts:match.

The ?delimStart and ?delimEnd parameters allow specifying the delimiters of the match strings inside the snippet.

The ?ellipsis parameter allows specifying the string used to separate distant matches in the snippet string.

The ?numTokens parameter specifies the number of tokens the returned string should containt at most.

URI functions

`tracker:uri-is-parent`

tracker:uri-is-parent (?parent, ?uri)

Returns a boolean value expressing whether ?parent is a parent of ?uri.

`tracker:uri-is-descendant`

tracker:uri-is-descendant (?uri1, ?uri2, ..., ?uriN, ?child)

Returns a boolean value expressing whether one of the given URIs are a parent (direct or indirect) of ?child.

`tracker:string-from-filename`

tracker:string-from-filename (?filename)

Returns a UTF-8 string from a filename.

Geolocation functions

`tracker:cartesian-distance`

tracker:cartesian-distance (?lat1, ?lat2, ?lon1, ?lon2)

Calculates the cartesian distance between 2 points expressed by ?lat1 / ?lon1 and ?lat2 / ?lon2.

`tracker:haversine-distance`

tracker:haversine-distance (?lat1, ?lat2, ?lon1, ?lon2)

Calculates the haversine distance between 2 points expressed by ?lat1 / ?lon1 and ?lat2 / ?lon2.

Identification functions

`tracker:id`

tracker:id (?urn)

Returns the internal ID corresponding to a URN. Its inverse operation is tracker:uri.

`tracker:uri`

tracker:uri (?id)

Returns the URN that corresponds to an ID. Its inverse operation is tracker:id

Full-text search

Full-text search (FTS) is a built-in feature of Tracker, it allows for efficient search of individual terms across large collections of text.

String properties are not searchable through the full-text index by default, only properties with the nrl:fulltextIndexed property enabled can be searched with FTS.

# Enable FTS search on the example:title property
example:title a rdf:Property;
  rdfs:range xsd:string ;
  nrl:fulltextIndexed true .

Multiple full-text indexed properties may be defined, either in the same or different classes.

In order to tap into the full-text search index, the SPARQL query must use the fts:match pseudo-property, e.g.:

SELECT ?res { ?res fts:match "term1 term2" }

This property will match the resources that match the search terms, independently of the order and separation between those terms in the searched text. Any full-text indexed property is candidate for these matches.

In order to complement this pseudo-property, there are additional functions to extract more information from the full-text index:

fts:rank to get a ranking order for the matched element. To be used in ORDER BY clauses.
fts:offsets to get a list of offsets of the lookup terms as found in the searched text.
fts:snippet to get a short string representation of the lookup terms in the searched text.

These functions work on each of the matches provided by fts:match, the following example puts all FTS features together at work:

# Get resource IRI, snippet and match offsets of every
# document matching "GNOME"
SELECT
  ?u
  fts:snippet(?u)
  fts:offsets(?u)
{
  ?u a nfo:Document ;
    fts:match "GNOME" .
}
ORDER BY DESC (fts:rank(?u))

Full-text search is case insensitive, and the content of its index may be subject to stemming, stop word lists and other methods of pre-processing, these settings may changed via the TrackerSparqlConnectionFlags set on a local connection.