+++ /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>
- * 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.
- */
- public void refresh() 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. 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