java - Once I've written a builtin, what do I need to do to make the reasoners aware of it?

Question

I have written a custom builtin to use in my Project but I do not really know how I can use it. I have written two classes. In one of them there is the builtin I have made (using BaseBuiltin) and in the other one I have registered the new builtin (using BuiltinRegistry).

I have already tried to use default builtins, writing rules that use them in a text file readable from Eclipse using Java. In this case I do not have any problems. How can I use the builtin I have built? Should I import (or include) something in some files?

Answer 1

First you define a Builtin, usually by extending BaseBuiltin, and then you use BuiltinRegistry.theRegistry.register(Builtin) to make it available to Jena rule-based inference.

Once you've done that, you need to actually use a rule that will reference your Builtin in order to trigger it.

BuiltinRegistry.theRegistry.register( new BaseBuiltin() {
    @Override
    public String getName() {
        return "example";
    }
    @Override
    public void headAction( final Node[] args, final int length, final RuleContext context ) {
        System.out.println("Head Action: "+Arrays.toString(args));
    }
} );

final String exampleRuleString =
    "[mat1: (?s ?p ?o)
-> print(?s ?p ?o),
   example(?s ?p ?o)
]"+
    "";
System.out.println(exampleRuleString);

/* I tend to use a fairly verbose syntax for parsing out my rules when I construct them
 * from a string. You can read them from whatever other sources.
 */
final List<Rule> rules;
try( final BufferedReader src = new BufferedReader(new InputStreamReader(new ByteArrayInputStream(exampleRuleString.getBytes()))) ) {
    rules = Rule.parseRules(Rule.rulesParserFromReader(src));
}

/* Construct a reasoner and associate the rules with it  */
final GenericRuleReasoner reasoner = (GenericRuleReasoner) GenericRuleReasonerFactory.theInstance().create(null);
reasoner.setRules(rules);

/* Create & Prepare the InfModel. If you don't call prepare, then
 * rule firings and inference may be deferred until you query the
 * model rather than happening at insertion. This can make you think
 * that your Builtin is not working, when it is.
 */
final InfModel infModel = ModelFactory.createInfModel(reasoner, ModelFactory.createDefaultModel());
infModel.prepare();

/* Add a triple to the graph: 
* [] rdf:type rdfs:Class
*/
infModel.createResource(RDFS.Class);

The output of this code will be:

• The string of the forward-chaining rule
• The result of calling the print Builtin
• The result of calling the example Builtin

... which is exactly what we see:

[mat1: (?s ?p ?o)
    -> print(?s ?p ?o),
       example(?s ?p ?o)
]
-2b47400d:14593fc1564:-7fff rdf:type rdfs:Class 
Head Action: [-2b47400d:14593fc1564:-7fff, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class]