/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.reasoner.rulesys.builtins;
import org.apache.jena.graph.* ;
import org.apache.jena.reasoner.rulesys.* ;
/**
* Can be used in two arg form (X, P) or three arg form (X, P, V).
* In three arg form it succeeds if the triple (X, P, V) is not
* currently present, in two arg form it succeeds if there is not value
* for (X, P, *).
*/
public class NoValue extends BaseBuiltin {
/**
* Return a name for this builtin, normally this will be the name of the
* functor that will be used to invoke it.
*/
@Override
public String getName() {
return "noValue";
}
/**
* This method is invoked when the builtin is called in a rule body.
* @param args the array of argument values for the builtin, this is an array
* of Nodes, some of which may be Node_RuleVariables.
* @param length the length of the argument list, may be less than the length of the args array
* for some rule engines
* @param context an execution context giving access to other relevant data
* @return return true if the buildin predicate is deemed to have succeeded in
* the current environment
*/
@Override
public boolean bodyCall(Node[] args, int length, RuleContext context) {
if (length !=2 && length != 3) {
throw new BuiltinException(this, context, "builtin " + getName() + " requires 2 or 3 arguments but saw " + length);
}
Node obj = null;
if (length == 3) {
obj = getArg(2, args, context);
}
Node subj = getArg(0, args, context);
// Allow variables in subject position to correspond to wild cards
if (subj.isVariable()) {
subj = null;
}
Node pred = getArg(1, args, context);
if (pred.isVariable()) {
pred = null;
}
return !context.contains(subj, pred, obj);
}
/**
* Flag as non-monotonic so the guard clause will get rerun after deferal
* as part of a non-trivial conflict set.
*/
@Override
public boolean isMonotonic() {
return false;
}
}