001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.commons.rdf.api;
019
020import java.util.Optional;
021
022/**
023 * A generalised "quad-like" interface, extended by {@link Quad}.
024 * <p>
025 * A QuadLike statement has at least a {@link #getSubject()},
026 * {@link #getPredicate()}, {@link #getObject()} and {@link #getGraphName()},
027 * but unlike a {@link Quad} does not have a formalised
028 * {@link Quad#equals(Object)} or {@link Quad#hashCode()} semantics and is not
029 * required to be <em>immutable</em> or <em>thread-safe</em>. This interface can
030 * also be used for <em>generalised quads</em> (e.g. a {@link BlankNode} as
031 * predicate).
032 * <p>
033 * Implementations should specialise which specific {@link RDFTerm} types they
034 * return by overriding {@link #getSubject()}, {@link #getPredicate()},
035 * {@link #getObject()} and {@link #getGraphName()}.
036 *
037 * @since 0.3.0-incubating
038 * @see Quad
039 */
040public interface QuadLike<G extends RDFTerm> extends TripleLike {
041
042    /**
043     * The graph name (graph label) of this statement, if present.
044     * <p>
045     * If {@link Optional#isPresent()}, then the {@link Optional#get()} indicate
046     * the graph name of this statement. If the graph name is not present,e.g.
047     * the value is {@link Optional#empty()}, it indicates that this Quad is in
048     * the default graph.
049     *
050     * @return If {@link Optional#isPresent()}, the graph name of this quad,
051     *         otherwise {@link Optional#empty()}, indicating the default graph.
052     *         The graph name is typically an {@link IRI} or {@link BlankNode}.
053     */
054    Optional<G> getGraphName();
055
056}