| /* |
| * 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.rya.api.function.sp; |
| |
| import static java.util.Objects.requireNonNull; |
| |
| import java.util.Optional; |
| |
| import org.eclipse.rdf4j.model.Statement; |
| import org.eclipse.rdf4j.model.Value; |
| import org.eclipse.rdf4j.query.BindingSet; |
| import org.eclipse.rdf4j.query.algebra.StatementPattern; |
| import org.eclipse.rdf4j.query.algebra.Var; |
| import org.eclipse.rdf4j.query.algebra.evaluation.QueryBindingSet; |
| |
| import edu.umd.cs.findbugs.annotations.DefaultAnnotation; |
| import edu.umd.cs.findbugs.annotations.NonNull; |
| import edu.umd.cs.findbugs.annotations.Nullable; |
| |
| /** |
| * Matches {@link Statement}s against a {@link StatementPattern} and returns {@link BindingSet}s |
| * when the statement matched the pattern. |
| */ |
| @DefaultAnnotation(NonNull.class) |
| public class StatementPatternMatcher { |
| |
| private final StatementPattern pattern; |
| |
| /** |
| * Constructs an instance of {@link StatementPatternMatcher}. |
| * |
| * @param pattern - The pattern that will be matched against. (not null) |
| */ |
| public StatementPatternMatcher(final StatementPattern pattern) { |
| this.pattern = requireNonNull(pattern); |
| } |
| |
| /** |
| * Matches a {@link Statement} against the provided {@link StatementPattern} and returns a {@link BindingSet} |
| * if the statement matched the pattern. |
| * |
| * @param statement - The statement that will be matched against the pattern. (not null) |
| * @return A {@link BinidngSet} containing the statement's values filled in for the pattern's variables if |
| * the statement's values match the pattern's constants; otherwise empty. |
| */ |
| public Optional<BindingSet> match(final Statement statement) { |
| requireNonNull(statement); |
| |
| // Setup the resulting binding set that could be built from this Statement. |
| final QueryBindingSet bs = new QueryBindingSet(); |
| |
| if(matchesValue(pattern.getSubjectVar(), statement.getSubject(), bs) && |
| matchesValue(pattern.getPredicateVar(), statement.getPredicate(), bs) && |
| matchesValue(pattern.getObjectVar(), statement.getObject(), bs) && |
| matchesContext(pattern.getContextVar(), statement.getContext(), bs)) { |
| return Optional.of(bs); |
| } else { |
| return Optional.empty(); |
| } |
| } |
| |
| /** |
| * The following table describes how a Subject, Predicate, and Object Var may be handled for a Statement and a |
| * Statement Pattern: |
| * <table border=1> |
| * <tr> <th>Pattern's var is constant</th> <th>Effect on resulting BS</th> </tr> |
| * <try> <td>yes</td> <td>Emit a BS if they match, no Context binding</td> </tr> |
| * <try> <td>no</td> <td>Emit a BS with a binding for the variable</td> </tr> |
| * </table> |
| * |
| * @param var - The statement pattern variable that is being matched. (not null) |
| * @param stmtValue - The statement's value for the variable. (not null) |
| * @param bs - The binding set that may be updated to include a binding for the variable. (not null) |
| * @return {@code true} if he variable and the statement value match, otherwise {@code false}, |
| */ |
| private boolean matchesValue(final Var var, final Value stmtValue, final QueryBindingSet bs) { |
| requireNonNull(var); |
| requireNonNull(stmtValue); |
| requireNonNull(bs); |
| |
| // If the var is a constant, statement's value must match the var's value. |
| if(var.isConstant()) { |
| if(!stmtValue.equals(var.getValue())) { |
| return false; |
| } |
| } else { |
| // Otherwise it is a variable to be filled in. |
| bs.addBinding(var.getName(), stmtValue); |
| } |
| |
| // Either the value matched the constant or the binding set was updated. |
| return true; |
| } |
| |
| /** |
| * The following table describes how Context may be handled for a Statement and a Statement Pattern: |
| * <table border=1> |
| * <tr> <th>Pattern's context state</th> <th>Statement has a context value</th> <th>Effect on resulting BS</th></tr> |
| * <tr> <td>not mentioned</td> <td>yes</td> <td>Emit BS without a Context binding</td> </tr> |
| * <tr> <td>not mentioned</td> <td>no</td> <td>Emit BS without a Context binding</td> </tr> |
| * <tr> <td>has a constant</td> <td>yes</td> <td>Emit BS if they match, no Context binding</td> </tr> |
| * <tr> <td>has a constant</td> <td>no</td> <td>Do not emit a BS</td> </tr> |
| * <tr> <td>has a variable</td> <td>yes</td> <td>Emit BS with Context binding</td> </tr> |
| * <tr> <td>has a variable</td> <td>no</td> <td>Do not emit a BS</td> </tr> |
| * </table> |
| * |
| * @param cntxVar - The statement pattern's context variable. This may be {@code null} when there is no context |
| * specified for the pattern. |
| * @param stmtCntx - The statement's context value. This may be {@code null} when there was no context |
| * specified within the statement. |
| * @param bs - The binding set that may be updated to include a context binding. (not null) |
| * @return {@code true} if the the pattern's context variable and statement's context matched, otherwise {@code false}. |
| */ |
| private boolean matchesContext(@Nullable final Var cntxVar, @Nullable final Value stmtCntx, final QueryBindingSet bs) { |
| if(cntxVar == null) { |
| // If there is no context, automatically matches. |
| return true; |
| } else if(stmtCntx == null) { |
| // If no value was provided within the statement, then it does not match. |
| return false; |
| } else { |
| // Otherwise handle it like a normal variable. |
| return matchesValue(cntxVar, stmtCntx, bs); |
| } |
| } |
| } |