Functions in ARQ

SPARQL allows custom functions in filter 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.

Function Library

The prefix afn is <http://jena.hpl.hp.com/ARQ/function#>.

Direct loading using a URI prefix of <java:com.hp.hpl.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).

XQuery/XPath functions and operators supported

String Functions

Function name	Description
`fn:contains(string, substr)`	Test whether `substr` occurs in string.
`fn:starts-with(string, match)`	Test whether `string` starts with `substr`.
`fn:ends-with(string, match)`	Test whether `string` ends with `substr.`
`fn:string-length(string)`	Return the length of a `string`.
`fn:lower-case(string)`	Return a string which is the lower case equivalent of the argument.
`fn:upper-case(string)`	Return a string which is the upper case equivalent of the argument.
`fn:matches(string, pattern [, flags])`	Regular expression match.
`fn:concat(string, ...)`	Return the concatenation of strings.
`fn:substring(string, begin [,length])`	Returns the substring of a `string`, given by `begin` (integer) and, optionally, length `length`.

Absence of length means to end of string. Strings are indexed from zero. - Strings start from one, not zero as they do in Java and C#. - The third argument is the length, like C# but unlike Java, where it is the endIndex.

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.

The operation afn:substring provides Java semantics.

Mathematical Functions

Function name	Description
`afn:min(num1, num2)`	Return the minimum of two expressions evaluating to numbers.
`afn:max(num1, num2)`	Return the maximum of two expressions evaluating to numbers.
`fn:round(v)`	Return the nearest integer value to the argument.
`fn:abs(v)`	Return the absolute value.
`fn:floor(v)`	Return the greatest integer value less than the argument (as a double).
`fn:ceiling(v)`	Return the smallest integer value than the argument (as a double).

Note: See also afn:min and afn:max for binary min and max functions.

Boolean Functions

Function name	Description
`fn:boolean(value)`	Boolean effective value of `value`.
`fn:not(value)`	Logical negation of the boolean effective value of `value`.

Functions provided by ARQ

RDF Graph Functions

Function name	Description
`afn:bnode(?x)`	Return the blank node label if ?x is a blank node.
`afn:localname(?x)`	The local name of ?x if a IRI. Based on splitting the IRI, not on any prefixes in the query or dataset.
`afn:namespace(?x)`	The namespace of ?x if a IRI. Based on splitting the IRI, not on any prefixes in the query or dataset.

String Functions

Function name	Description
`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.

Mathematical Functions

Function name	Description
`afn:min(num1, num2)`	Return the minimum of two expressions evaluating to numbers.
`afn:max(num1, num2)`	Return the maximum of two expressions evaluating to numbers.
`afn:pi()`	The value of pi, as an XSD double.
`afn:e()`	The value of e, as an XSD double.
`afn:sqrt(num)`	The square root of num.

Miscellaneous Functions

Function name	Description
`afn:now()`	Current time. Actually, the time the query started. Constant throughout a query execution.
`afn:sha1sum(resource)`	Calculate the SHA1 checksum of a literal or URI.