Droolsでの後方連鎖の例

query belongsTo(String x, String y)
    Fact(x, y;)
    or
    (Fact(z, y;) and belongsTo(x, z;))
end

rule "Great Wall of China BELONGS TO Planet Earth"
when
    belongsTo("Great Wall of China", "Planet Earth";)
then
    result.setValue("Decision one taken: Great Wall of China BELONGS TO Planet Earth");
end

rule "print all facts"
when
    belongsTo(element, place;)
then
    result.addFact(element + " IS ELEMENT OF " + place);
end

public class Fact {

    @Position(0)
    private String element;

    @Position(1)
    private String place;

   //getters, setters, constructors, and other methods ...
}

public class Result {
    private String value;
    private List<String> facts = new ArrayList<>();

   //... getters, setters, constructors, and other methods
}

public class BackwardChainingTest {

    @Before
    public void before() {
        result = new Result();
        ksession = new DroolsBeanFactory().getKieSession();
    }

    @Test
    public void whenWallOfChinaIsGiven__ThenItBelongsToPlanetEarth() {

        ksession.setGlobal("result", result);
        ksession.insert(new Fact("Asia", "Planet Earth"));
        ksession.insert(new Fact("China", "Asia"));
        ksession.insert(new Fact("Great Wall of China", "China"));

        ksession.fireAllRules();

        assertEquals(
          result.getValue(),
          "Decision one taken: Great Wall of China BELONGS TO Planet Earth");
    }
}