Tracker – 3.0: Builtin SPARQL functions
Description: Reference for Tracker-3.0: Builtin SPARQL functions

#### 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.