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* 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 com.hp.hpl.jena.reasoner.rulesys.builtins;
import com.hp.hpl.jena.graph.Graph;
import com.hp.hpl.jena.graph.Node;
import com.hp.hpl.jena.graph.Triple;
import com.hp.hpl.jena.reasoner.InfGraph;
import com.hp.hpl.jena.reasoner.TriplePattern;
import com.hp.hpl.jena.reasoner.rulesys.BuiltinException;
import com.hp.hpl.jena.reasoner.rulesys.RuleContext;
import com.hp.hpl.jena.reasoner.rulesys.Util;
/**
* A variant of the "remove" builtin that will delete matched triples
* from the graph but will not trigger further rule processing for
* the removed triples. This makes it seriously non-monotonic but
* useful for rewrite rules.
*/
public class Drop 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 "drop";
}
/**
* This method is invoked when the builtin is called in a rule head.
* Such a use is only valid in a forward rule.
* @param args the array of argument values for the builtin, this is an array
* of Nodes.
* @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
*/
@Override
public void headAction(Node[] args, int length, RuleContext context) {
boolean ok = false;
InfGraph inf = context.getGraph();
Graph raw = inf.getRawGraph();
Graph deductions = inf.getDeductionsGraph();
for (int i = 0; i < length; i++) {
Node clauseN = getArg(i, args, context);
if (Util.isNumeric(clauseN)) {
int clauseIndex = Util.getIntValue(clauseN);
Object clause = context.getRule().getBodyElement(clauseIndex);
if (clause instanceof TriplePattern) {
Triple t = context.getEnv().instantiate((TriplePattern)clause);
raw.delete(t);
deductions.delete(t);
} else {
throw new BuiltinException(this, context, "illegal triple to remove non-triple clause");
}
} else {
throw new BuiltinException(this, context, "illegal arg to remove (" + clauseN + "), must be an integer");
}
}
}
/**
* Returns false if this builtin is non-monotonic. This includes non-monotonic checks like noValue
* and non-monotonic actions like remove/drop. A non-monotonic call in a head is assumed to
* be an action and makes the overall rule and ruleset non-monotonic.
* Most JenaRules are monotonic deductive closure rules in which this should be false.
*/
@Override
public boolean isMonotonic() {
return false;
}
}