Github user ajs6f commented on a diff in the pull request:
https://github.com/apache/jena/pull/94#discussion_r44410251
--- Diff:
jena-arq/src/main/java/org/apache/jena/sparql/core/mem/QuadTable.java ---
@@ -0,0 +1,59 @@
+/*
+ * 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.core.mem;
+
+import static org.apache.jena.graph.Node.ANY;
+
+import java.util.stream.Stream;
+
+import org.apache.jena.graph.Node;
+import org.apache.jena.sparql.core.Quad;
+
+/**
+ * A simplex or multiplex table of {@link Quad}s. Implementations may wish
to override {@link #listGraphNodes()} with a
+ * more efficient implementation.
+ *
+ */
+public interface QuadTable extends TupleTable<Quad> {
+
+ /**
+ * Search the table using a pattern of slots. {@link Node#ANY} or
<code>null</code> will work as a wildcard.
+ *
+ * @param g the graph node of the pattern
+ * @param s the subject node of the pattern
+ * @param p the predicate node of the pattern
+ * @param o the object node of the pattern
+ * @return an {@link Stream} of matched quads
+ */
+ Stream<Quad> find(Node g, Node s, Node p, Node o);
+
+ /**
+ * Discover the graphs named in the table
+ *
+ * @return an {@link Stream} of graph names used in this table
+ */
+ default Stream<Node> listGraphNodes() {
+ return find(ANY, ANY, ANY, ANY).map(Quad::getGraph).distinct();
+ }
--- End diff --
See my comment on `DatasetGraphInMemory` as to union graph functionality.
It applies here too. This is an interface which has no reason or right to
assume anything about adjacency.
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