--- /dev/null
+package org.apache.lucene.facet.taxonomy;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.Map;
+
+/**
+ * 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.
+ */
+
+/**
+ * TaxonomyReader is the read-only interface with which the faceted-search
+ * library uses the taxonomy during search time.
+ * <P>
+ * A TaxonomyReader holds a list of categories. Each category has a serial
+ * number which we call an "ordinal", and a hierarchical "path" name:
+ * <UL>
+ * <LI>
+ * The ordinal is an integer that starts at 0 for the first category (which is
+ * always the root category), and grows contiguously as more categories are
+ * added; Note that once a category is added, it can never be deleted.
+ * <LI>
+ * The path is a CategoryPath object specifying the category's position in the
+ * hierarchy.
+ * </UL>
+ * <B>Notes about concurrent access to the taxonomy:</B>
+ * <P>
+ * An implementation must allow multiple readers to be active concurrently
+ * with a single writer. Readers follow so-called "point in time" semantics,
+ * i.e., a TaxonomyReader 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>
+ * In faceted search, two separate indices are used: the main Lucene index,
+ * and the taxonomy. Because the main index refers to the categories listed
+ * in the taxonomy, it is important to open the taxonomy *after* opening the
+ * main index, and it is also necessary to reopen() the taxonomy after
+ * reopen()ing the main index.
+ * <P>
+ * This order is important, otherwise it would be possible for the main index
+ * to refer to a category which is not yet visible in the old snapshot of
+ * the taxonomy. Note that it is indeed fine for the the taxonomy to be opened
+ * after the main index - even a long time after. The reason is that once
+ * a category is added to the taxonomy, it can never be changed or deleted,
+ * so there is no danger that a "too new" taxonomy not being consistent with
+ * an older index.
+ *
+ * @lucene.experimental
+ */
+public interface TaxonomyReader extends Closeable {
+
+ /**
+ * The root category (the category with the empty path) always has the
+ * ordinal 0, to which we give a name ROOT_ORDINAL.
+ * getOrdinal() of an empty path will always return ROOT_ORDINAL, and
+ * getCategory(ROOT_ORDINAL) will return the empty path.
+ */
+ public final static int ROOT_ORDINAL = 0;
+
+ /**
+ * Ordinals are always non-negative, so a negative ordinal can be used to
+ * signify an error. Methods here return INVALID_ORDINAL (-1) in this case.
+ */
+ public final static int INVALID_ORDINAL = -1;
+
+ /**
+ * getOrdinal() returns the ordinal of the category given as a path.
+ * The ordinal is the category's serial number, an integer which starts
+ * with 0 and grows as more categories are added (note that once a category
+ * is added, it can never be deleted).
+ * <P>
+ * If the given category wasn't found in the taxonomy, INVALID_ORDINAL is
+ * returned.
+ */
+ public int getOrdinal(CategoryPath categoryPath) throws IOException;
+
+ /**
+ * getPath() returns the path name of the category with the given
+ * ordinal. The path is returned as a new CategoryPath object - to
+ * reuse an existing object, use {@link #getPath(int, CategoryPath)}.
+ * <P>
+ * A null is returned if a category with the given ordinal does not exist.
+ */
+ public CategoryPath getPath(int ordinal) throws IOException;
+
+ /**
+ * getPath() returns the path name of the category with the given
+ * ordinal. The path is written to the given CategoryPath object (which
+ * is cleared first).
+ * <P>
+ * If a category with the given ordinal does not exist, the given
+ * CategoryPath object is not modified, and the method returns
+ * <code>false</code>. Otherwise, the method returns <code>true</code>.
+ */
+ public boolean getPath(int ordinal, CategoryPath result) throws IOException;
+
+ /**
+ * refresh() re-reads the taxonomy information if there were any changes to
+ * the taxonomy since this instance was opened or last refreshed. Calling
+ * refresh() is more efficient than close()ing the old instance and opening a
+ * new one.
+ * <P>
+ * If there were no changes since this instance was opened or last refreshed,
+ * then this call does nothing. Note, however, that this is still a relatively
+ * slow method (as it needs to verify whether there have been any changes on
+ * disk to the taxonomy), so it should not be called too often needlessly. In
+ * faceted search, the taxonomy reader's refresh() should be called only after
+ * a reopen() of the main index.
+ * <P>
+ * Refreshing the taxonomy might fail in some cases, for example
+ * if the taxonomy was recreated since this instance was opened or last refreshed.
+ * In this case an {@link InconsistentTaxonomyException} is thrown,
+ * suggesting that in order to obtain up-to-date taxonomy data a new
+ * {@link TaxonomyReader} should be opened. Note: This {@link TaxonomyReader}
+ * instance remains unchanged and usable in this case, and the application can
+ * continue to use it, and should still {@link #close()} when no longer needed.
+ * <P>
+ * It should be noted that refresh() is similar in purpose to
+ * IndexReader.reopen(), but the two methods behave differently. refresh()
+ * refreshes the existing TaxonomyReader object, rather than opening a new one
+ * in addition to the old one as reopen() does. The reason is that in a
+ * taxonomy, one can only add new categories and cannot modify or delete
+ * existing categories; Therefore, there is no reason to keep an old snapshot
+ * of the taxonomy open - refreshing the taxonomy to the newest data and using
+ * this new snapshots in all threads (whether new or old) is fine. This saves
+ * us needing to keep multiple copies of the taxonomy open in memory.
+ * @return true if anything has changed, false otherwise.
+ */
+ public boolean refresh() throws IOException, InconsistentTaxonomyException;
+
+ /**
+ * 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. However, implementations are
+ * expected to provide a much more efficient implementation:
+ * <P>
+ * getParent() should be a very quick method, as it is used during the
+ * facet aggregation process in faceted search. Implementations will most
+ * likely want to serve replies to this method from a pre-filled cache.
+ * <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.
+ */
+ public int getParent(int ordinal) throws IOException;
+
+ /**
+ * getParentArray() returns an int array of size getSize() listing the
+ * ordinal of the parent category of each category in the taxonomy.
+ * <P>
+ * The caller can hold on to the array it got indefinitely - it is
+ * guaranteed that no-one else will modify it. The other side of the
+ * same coin is that the caller must treat the array it got as read-only
+ * and <B>not modify it</B>, because other callers might have gotten the
+ * same array too (and getParent() calls might be answered from the
+ * same array).
+ * <P>
+ * If you use getParentArray() instead of getParent(), remember that
+ * the array you got is (naturally) not modified after a refresh(),
+ * so you should always call getParentArray() again after a refresh().
+ * <P>
+ * This method's function is similar to allocating an array of size
+ * getSize() and filling it with getParent() calls, but implementations
+ * are encouraged to implement it much more efficiently, with O(1)
+ * complexity. This can be done, for example, by the implementation
+ * already keeping the parents in an array, and just returning this
+ * array (without any allocation or copying) when requested.
+ */
+ public int[] getParentArray() throws IOException;
+
+ /**
+ * Equivalent representations of the taxonomy's parent info,
+ * used internally for efficient computation of facet results:
+ * "youngest child" and "oldest sibling"
+ */
+ public static interface ChildrenArrays {
+ /**
+ * getYoungestChildArray() returns an int array of size getSize()
+ * listing the ordinal of the youngest (highest numbered) child
+ * category of each category in the taxonomy. The value for a leaf
+ * category (a category without children) is
+ * <code>INVALID_ORDINAL</code>.
+ */
+ public int[] getYoungestChildArray();
+ /**
+ * getOlderSiblingArray() returns an int array of size getSize()
+ * listing for each category the ordinal of its immediate older
+ * sibling (the sibling in the taxonomy tree with the highest ordinal
+ * below that of the given ordinal). The value for a category with no
+ * older sibling is <code>INVALID_ORDINAL</code>.
+ */
+ public int[] getOlderSiblingArray();
+ }
+
+ /**
+ * getChildrenArrays() returns a {@link ChildrenArrays} object which can
+ * be used together to efficiently enumerate the children of any category.
+ * <P>
+ * The caller can hold on to the object it got indefinitely - it is
+ * guaranteed that no-one else will modify it. The other side of the
+ * same coin is that the caller must treat the object which it got (and
+ * the arrays it contains) as read-only and <B>not modify it</B>, because
+ * other callers might have gotten the same object too.
+ * <P>
+ * Implementations should have O(getSize()) time for the first call or
+ * after a refresh(), but O(1) time for further calls. In neither case
+ * there should be a need to read new data from disk. These guarantees
+ * are most likely achieved by calculating this object (based on the
+ * getParentArray()) when first needed, and later (if the taxonomy was not
+ * refreshed) returning the same object (without any allocation or copying)
+ * when requested.
+ * <P>
+ * The reason we have one method returning one object, rather than two
+ * methods returning two arrays, is to avoid race conditions in a multi-
+ * threaded application: We want to avoid the possibility of returning one
+ * new array and one old array, as those could not be used together.
+ */
+ public ChildrenArrays getChildrenArrays();
+
+ /**
+ * Retrieve user committed data.
+ * @see TaxonomyWriter#commit(Map)
+ */
+ public Map<String, String> getCommitUserData();
+
+ /**
+ * Expert: increments the refCount of this TaxonomyReader instance.
+ * RefCounts can be used to determine when a taxonomy reader can be closed
+ * safely, i.e. as soon as there are no more references.
+ * Be sure to always call a corresponding decRef(), in a finally clause;
+ * otherwise the reader may never be closed.
+ */
+ public void incRef();
+
+ /**
+ * Expert: decreases the refCount of this TaxonomyReader instance.
+ * If the refCount drops to 0, then pending changes (if any) can be
+ * committed to the taxonomy index and this reader can be closed.
+ * @throws IOException
+ */
+ public void decRef() throws IOException;
+
+ /**
+ * Expert: returns the current refCount for this taxonomy reader
+ */
+ public int getRefCount();
+
+ /**
+ * 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