| /* |
| * 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.sparql.algebra.optimize; |
| |
| import org.apache.jena.sparql.algebra.Op ; |
| import org.apache.jena.sparql.algebra.TransformCopy ; |
| import org.apache.jena.sparql.algebra.op.OpAssign ; |
| import org.apache.jena.sparql.algebra.op.OpExtend ; |
| import org.apache.jena.sparql.core.VarExprList ; |
| |
| /** |
| * An optimizer that aims to combine multiple extend clauses together. |
| * <p> |
| * Since the semantics of extend are such that the expressions are expected to |
| * be evaluated in order we can combine extends together. This can make |
| * evaluation more efficient because all the assignments are done in a single |
| * step though depending on the underlying store this may make little or no |
| * difference. |
| * </p> |
| * <p> |
| * Note that standard algebra construction will cause much of this to happen |
| * naturally but sometimes it is useful to apply this as an additional |
| * independent transform. |
| * </p> |
| * |
| */ |
| public class TransformExtendCombine extends TransformCopy { |
| |
| public TransformExtendCombine() {} |
| |
| @Override |
| public Op transform(OpAssign opAssign, Op subOp) { |
| if (subOp instanceof OpAssign) { |
| // If a variable is assigned twice, don't do anything. |
| // (assign (?x 2) (assign (?x 1) op)) => leave alone. |
| // This is the safest option in a rare case. |
| // It would be OK if addAll does a replacement without checking |
| // but having it check and complain about duplicates adds robustness. |
| // In OpExtend, it's actually illegal. |
| |
| OpAssign x = (OpAssign)subOp ; |
| VarExprList outerVarExprList = opAssign.getVarExprList() ; |
| VarExprList innerVarExprList = new VarExprList(x.getVarExprList()) ; // Copy |
| |
| Op r = OpAssign.assign(x.getSubOp(), innerVarExprList) ; |
| // This contains an "if already (assign)" test. |
| r = OpAssign.assign(r, outerVarExprList) ; |
| return r ; |
| } |
| return super.transform(opAssign, subOp); |
| } |
| |
| @Override |
| public Op transform(OpExtend opExtend, Op subOp) { |
| if (subOp instanceof OpExtend) { |
| // The case of (extend (?x e1) (extend (?x e2) ...op...)) |
| // is actually illegal in SPARQL. ?x must be a fresh variable. |
| OpExtend x = (OpExtend)subOp ; |
| VarExprList outerVarExprList = opExtend.getVarExprList() ; |
| VarExprList innerVarExprList = new VarExprList(x.getVarExprList()) ; // Copy |
| Op r = OpExtend.extend(x.getSubOp(), innerVarExprList) ; |
| // This contains an "if already (extend)" test. |
| r = OpExtend.extend(r, outerVarExprList) ; |
| return r ; |
| } |
| return super.transform(opExtend, subOp); |
| } |
| } |