com.hp.hpl.jena.reasoner.rulesys
Interface Builtin

All Known Implementing Classes:
BaseBuiltin

public interface Builtin

Rules employ builtins to do all tests and actions other than simple triple matches and triple creation.

Builtins can be invoked in two contexts. In the head of forward rules they perform some action based on the variable bindings generated by the body and additional context (the graph being reasoned over, the set of triples bound by the body). In the body of rules they perform tests, and additional variable bindings.

The mapping from the rule definition (which uses functors to hold the parsed call) to the java implementation of the builtin is done via the BuiltinRegistry which can be user extended.

Version:
$Revision: 1.6 $ on $Date: 2003/08/27 13:09:18 $
Author:
Dave Reynolds

Method Summary
 boolean bodyCall(Node[] args, int length, RuleContext context)
          This method is invoked when the builtin is called in a rule body.
 int getArgLength()
          Return the expected number of arguments for this functor or 0 if the number is flexible.
 java.lang.String getName()
          Return a convenient name for this builtin, normally this will be the name of the functor that will be used to invoke it and will often be the final component of the URI.
 java.lang.String getURI()
          Return the full URI which identifies this built in.
 void headAction(Node[] args, int length, RuleContext context)
          This method is invoked when the builtin is called in a rule head.
 boolean isSafe()
          Returns false if this builtin has side effects when run in a body clause, other than the binding of environment variables.
 

Method Detail

getName

public java.lang.String getName()
Return a convenient name for this builtin, normally this will be the name of the functor that will be used to invoke it and will often be the final component of the URI.


getURI

public java.lang.String getURI()
Return the full URI which identifies this built in.


getArgLength

public int getArgLength()
Return the expected number of arguments for this functor or 0 if the number is flexible.


bodyCall

public boolean bodyCall(Node[] args,
                        int length,
                        RuleContext context)
This method is invoked when the builtin is called in a rule body.

Parameters:
args - the array of argument values for the builtin, this is an array of Nodes, some of which may be Node_RuleVariables.
length - the length of the argument list, may be less than the length of the args array for some rule engines
context - an execution context giving access to other relevant data
Returns:
return true if the buildin predicate is deemed to have succeeded in the current environment

headAction

public void headAction(Node[] args,
                       int length,
                       RuleContext context)
This method is invoked when the builtin is called in a rule head. Such a use is only valid in a forward rule.

Parameters:
args - the array of argument values for the builtin, this is an array of Nodes.
length - the length of the argument list, may be less than the length of the args array for some rule engines
context - an execution context giving access to other relevant data

isSafe

public boolean isSafe()
Returns false if this builtin has side effects when run in a body clause, other than the binding of environment variables.



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