--- /dev/null
+package org.apache.lucene.facet.taxonomy;
+
+import java.io.Closeable;
+import java.io.IOException;
+
+import org.apache.lucene.util.TwoPhaseCommit;
+
+/**
+ * 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.
+ */
+
+/**
+ * TaxonomyWriter is the interface which the faceted-search library uses
+ * to dynamically build the taxonomy at indexing time.
+ * <P>
+ * Notes about concurrent access to the taxonomy:
+ * <P>
+ * An implementation must allow multiple readers and a single writer to be
+ * active concurrently. Readers follow so-called "point in time" semantics,
+ * i.e., a reader object will only see taxonomy entries which were available
+ * at the time it was created. What the writer writes is only available to
+ * (new) readers after the writer's commit() is called.
+ * <P>
+ * Faceted search keeps two indices - namely Lucene's main index, and this
+ * taxonomy index. When one or more readers are active concurrently with the
+ * writer, care must be taken to avoid an inconsistency between the state of
+ * these two indices: When writing to the indices, the taxonomy must always
+ * be committed to disk *before* the main index, because the main index
+ * refers to categories listed in the taxonomy.
+ * Such control can best be achieved by turning off the main index's
+ * "autocommit" feature, and explicitly calling commit() for both indices
+ * (first for the taxonomy, then for the main index).
+ * In old versions of Lucene (2.2 or earlier), when autocommit could not be
+ * turned off, a more complicated solution needs to be used. E.g., use
+ * some sort of (possibly inter-process) locking to ensure that a reader
+ * is being opened only right after both indices have been flushed (and
+ * before anything else is written to them).
+ *
+ * @lucene.experimental
+ */
+public interface TaxonomyWriter extends Closeable, TwoPhaseCommit {
+
+ /**
+ * addCategory() adds a category with a given path name to the taxonomy,
+ * and returns its ordinal. If the category was already present in
+ * the taxonomy, its existing ordinal is returned.
+ * <P>
+ * Before adding a category, addCategory() makes sure that all its
+ * ancestor categories exist in the taxonomy as well. As result, the
+ * ordinal of a category is guaranteed to be smaller then the ordinal of
+ * any of its descendants.
+ */
+ public int addCategory(CategoryPath categoryPath) throws IOException;
+
+ /**
+ * getParent() returns the ordinal of the parent category of the category
+ * with the given ordinal.
+ * <P>
+ * When a category is specified as a path name, finding the path of its
+ * parent is as trivial as dropping the last component of the path.
+ * getParent() is functionally equivalent to calling getPath() on the
+ * given ordinal, dropping the last component of the path, and then calling
+ * getOrdinal() to get an ordinal back.
+ * <P>
+ * If the given ordinal is the ROOT_ORDINAL, an INVALID_ORDINAL is returned.
+ * If the given ordinal is a top-level category, the ROOT_ORDINAL is returned.
+ * If an invalid ordinal is given (negative or beyond the last available
+ * ordinal), an ArrayIndexOutOfBoundsException is thrown. However, it is
+ * expected that getParent will only be called for ordinals which are
+ * already known to be in the taxonomy.
+ * TODO (Facet): instead of a getParent(ordinal) method, consider having a
+ * <P>
+ * getCategory(categorypath, prefixlen) which is similar to addCategory
+ * except it doesn't add new categories; This method can be used to get
+ * the ordinals of all prefixes of the given category, and it can use
+ * exactly the same code and cache used by addCategory() so it means less code.
+ */
+ public int getParent(int ordinal) throws IOException;
+
+ /**
+ * getSize() returns the number of categories in the taxonomy.
+ * <P>
+ * Because categories are numbered consecutively starting with 0, it
+ * means the taxonomy contains ordinals 0 through getSize()-1.
+ * <P>
+ * Note that the number returned by getSize() is often slightly higher
+ * than the number of categories inserted into the taxonomy; This is
+ * because when a category is added to the taxonomy, its ancestors
+ * are also added automatically (including the root, which always get
+ * ordinal 0).
+ */
+ public int getSize();
+
+}
fnp / pylucene.git / blobdiff