Apache Jena - Functions in ARQ

The regular expressions for fan:localname and afn:namespace were incorrect. SPARQL allows custom functions in expressions so that queries can be used on domain-specific data. SPARQL defines a function by URI (or prefixed name) in FILTER expressions. ARQ provides a function library and supports application-provided functions. Functions and property functions can be registered or dynamically loaded.

Applications can also provide their own functions.

ARQ also provides an implementation the Leviathan Function Library.

XQuery/XPath Functions and Operators supported

ARQ supports the scalar functions and operators from “XQuery 1.0 and XPath 2.0 Functions and Operators v3.1”.

Functions in involving sequences are not supported.

See XSD Support for details of datatypes and functions currently supported. To check the exact current registrations, see function/StandardFunctions.java.

See also the property functions library page.

Function Library

The prefix afn is <http://jena.apache.org/ARQ/function#>. (The old prefix of <http://jena.hpl.hp.com/ARQ/function#> continues to work. Applications are encouraged to switch.)

Direct loading using a URI prefix of <java:org.apache.jena.sparql.function.library.> (note the final dot) is deprecated.

The prefix fn is <http://www.w3.org/2005/xpath-functions#> (the XPath and XQuery function namespace).

The prefix math is <http://www.w3.org/2005/xpath-functions/math#>.

Custom Aggregates

The prefix agg: is <http://jena.apache.org/ARQ/function/aggregate#>.

The statistical aggregates are provided are:

agg:stdev, agg:stdev_samp, agg:stdev_pop, agg:variance, agg:var_samp, agg:var_pop

These are modelled after SQL aggregate functions STDEV, STDEV_SAMP, STDEV_POP, VARIANCE, VAR_SAMP, VAR_POP.

These, as keywords, are available in ARQ’s extended SPARQL (parse using Syntax.syntaxARQ).

Additional Functions Provided by ARQ

Most of these have equivalents, or near equivalents, in SPARQL or as an XQuery function and are to be preferred. These ARQ-specific versions remain for compatibility.

RDF Graph Functions

Function name	Description	Alternative
`afn:bnode(?x)`	Return the blank node label if ?x is a blank node.	`STR(?x)`
`afn:localname(?x)`	The local name of ?x	`REPLACE(STR(?x), "^(.)(/\|#)([^#/])$", "$3")`
`afn:namespace(?x)`	The namespace of ?x	`REPLACE(STR(?x), "^(.)(/\|#)([^#/])$", "$1")`

The prefix and local name of a IRI is based on splitting the IRI, not on any prefixes in the query or dataset.

String Functions

Function name	Description	Alternative
`afn:sprintf(format, v1, v2, ...)`	Make a string from the format string and the RDF terms.
`afn:substr(string, startIndex [,endIndex])`	Substring, Java style using `startIndex` and `endIndex`.
`afn:substring`	Synonym for afn:substr
`afn:strjoin(sep, string ...)`	Concatenate string together, with a separator.
`afn:sha1sum(resource)`	Calculate the SHA1 checksum of a literal or URI	`SHA1(STR(resource))`

Notes:

Strings in “XQuery 1.0 and XPath 2.0 Functions and Operators” start from character position one, unlike Java and C# where strings start from zero.
The fn:substring operation takes an optional length, like C# but different from Java, where it is the endIndex of the first character after the substring.
afn:substr uses Java-style startIndex and endIndex.

Mathematical Functions

Function name	Description	Alternative
`afn:min(num1, num2)`	Return the minimum of two numbers	`fn:min`
`afn:max(num1, num2)`	Return the maximum of two numbers	`fn:max`
`afn:pi()`	The value of pi, as an XSD double	`math:pi()`
`afn:e()`	The value of e, as an XSD double	`math:exp(1)`
`afn:sqrt(num)`	The square root of num	`math:sqrt`

Miscellaneous Functions

Function name	Description	Alternative
`afn:now()`	Current time. Actually, the time the query started.	`NOW()`
`afn:sha1sum(resource)`	Calculate the SHA1 checksum	`SHASUM`