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SirixDB is a hybrid on-disk and in-memory document oriented, versioned database system. It has a lightweight buffer manager, stores everything in a huge persistent and durable tree and allows efficient reconstruction of every revision. Furthermore, SirixDB implements change tracking, diffing and supports time travel queries.

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/**
 * Copyright (c) 2011, University of Konstanz, Distributed Systems Group All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met: * Redistributions of source code must retain the
 * above copyright notice, this list of conditions and the following disclaimer. * Redistributions
 * in binary form must reproduce the above copyright notice, this list of conditions and the
 * following disclaimer in the documentation and/or other materials provided with the distribution.
 * * Neither the name of the University of Konstanz nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL  BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package io.sirix.api;

import io.sirix.node.interfaces.Node;

/**
 * 
 * Data structure to store  XDM items.
 * 
 * 
 * This structure is used to store atomic values that are needed for the evaluation of a query. They
 * can be results of a query expression or be specified directly in the query e.g. as literals
 * perform an arithmetic operation or a comparison.
 * 
 * 
 * Since these items have to be distinguishable from nodes their key will be a negative long value
 * (node key is always a positive long value). This value is retrieved by negate their index in the
 * internal data structure.
 * 
 */
public interface ItemList {

  /**
   * Adds an item to the item list and assigns a unique item key to the item and return it. The item
   * key is the negatived index of the item in the item list. The key is negatived to make it
   * distinguishable from a node.
   * 
   * @param pNode the item to add
   * @return the item key
   */
  int addItem(final T pNode);

  /**
   * Returns the item at a given index in the item list. If the given index is the item key, it has
   * to be negated before.
   * 
   * @param pKey key of the item, that should be returned
   * @return item at the given index
   */
  T getItem(final long pKey);

  /**
   * Determines how many items are in the list.
   * 
   * @return list size
   */
  int size();
}