Title: 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](extension.html).

See also the [free text search](/documentation/larq/) page.

See also the [property functions](library-propfunc.html) library
page.

Applications can also
[provide their own functions](writing_functions.html).

## 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:

1.  Strings in
    "[XQuery 1.0 and XPath 2.0 Functions and Operators](http://www.w3.org/TR/xpath-functions/)"
    start from character position one, unlike Java and C\# where
    strings start from zero.
2.  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.