Package com.complexible.stardog.plan.filter.functions

Interface Function

All Superinterfaces:

Copyable<com.complexible.stardog.plan.filter.Expression>, com.complexible.stardog.plan.filter.Expression

All Known Subinterfaces:

Aggregate

All Known Implementing Classes:

AbstractFunction

public interface Function
extends com.complexible.stardog.plan.filter.Expression

This is the extension point for 17.6 (Extensible Value Testing) of the SPARQL spec.

For implementations of Function to be visible to the query parser and engine, they must be registered via the JDK ServiceLoader. Create a file called com.complexible.stardog.plan.filter.functions.Function in the META-INF/services directory. The contents of this file should be all of the *fully-qualified* class names for the custom Functions. Then if a jar containing the META-INF/services directory and the implementations for the Functions is included on the classpath, Stardog will pick up the implementations on startup.

To use the example from the SPARQL spec, if the Function is used in a query aGeo:distance(?axLoc, ?ayLoc, ?bxLoc, ?byLoc) , its signature is as follows:

 {code
      xsd:double   aGeo:distance (numeric x1, numeric y1, numeric x2, numeric y2)
 }
 

When evaluate is called, it will be provided four values via the ValueSolution, which are the current values for the parameters, x1, y1, x2, and y2.

Since:

0.1

Version:

3.0

Author:

Michael Grove

See Also:

• FunctionRegistry
• Extension Functions

Method Summary

Modifier and Type	Method	Description
Function	copy()	Create a deep copy of the object which does not share any references with the original.
default String	getDescription()	Return a description of the function suitable to be included in user manual.
String	getName()	Return the string that uniquely identifies this Expression, which should be a fully qualified URI.
List<String>	getNames()	Return all the strings that uniquely identifies this Function.
default void	initialize()	Initialize this function.
default boolean	isDeterministic()	Returns true if the function result is uniquely determined by its inputs or false if the function may return different results for the same inputs.

Methods inherited from interface com.complexible.stardog.plan.filter.Expression

accept, couldRaiseError, evaluate, getArgs, getCategory, replaceArg, setArgs

Method Details

getName

String getName()

Return the string that uniquely identifies this Expression, which should be a fully qualified URI. This URI is what is used to reference this Expression in a SPARQL query.

Returns:

the URI

getNames

List<String> getNames()

Return all the strings that uniquely identifies this Function. A function may have different names in different namespaces.

Returns:

all aliases of this Function

See Also:

• getName()

getDescription

default String getDescription()

Return a description of the function suitable to be included in user manual.

Returns:

description of the function

initialize

default void initialize()

Initialize this function. In the case of a pure function, this is a no-op. However, in some cases, a function needs to keep some global state during query execution for it to work correctly. initialize should prepare the function for execution by either clearing or otherwise preparing it's state for (re)execution.

copy

Function copy()

Create a deep copy of the object which does not share any references with the original.

Specified by:

copy in interface Copyable<com.complexible.stardog.plan.filter.Expression>

Returns:

a copy of the object

isDeterministic

default boolean isDeterministic()

Returns true if the function result is uniquely determined by its inputs or false if the function may return different results for the same inputs. If the function has no inputs then every invocation should always return the same value for it to be deterministic, e.g. PI(), whereas a function like UUID() is not deterministic.

Returns:

true if the function is deterministic