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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.service.xml.xpath;

/**
 * Enum represents different states of the result order that help to specify, if the result query
 * will be in document order or not.
 */
public enum OrdState {

  /** State of the HiddersMichiels - automaton. */
  LIN {

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdChild() {
      mOrdRank++;
      return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdParent() {
      if (mOrdRank > 0) {
        mOrdRank--;
      }
      return this;
    }
  },

  /** State of the HiddersMichiels - automaton. */
  MAX1 {

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdChild() {
      return OrdState.GENSIB;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdDesc() {
      return OrdState.SIB;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdFollPre() {
      return OrdState.SIB;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdFollPreSib() {
      return OrdState.GENSIB;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdAncestor() {
      return OrdState.LIN;
    }
  },

  /** State of the HiddersMichiels - automaton. */
  GENSIB {

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdChild() {
      return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdParent() {
      return OrdState.GEN;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdDesc() {
      return OrdState.SIB;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdFollPreSib() {
      mOrdRank++;
      return OrdState.GEN;

    }
  },

  /** State of the HiddersMichiels - automaton. */
  GEN {

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdChild() {
      mOrdRank++;
      return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdParent() {
      if (mOrdRank > 0) {
        mOrdRank--;
      }
      return this;
    }
  },

  /** State of the HiddersMichiels - automaton. */
  SIB {

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdChild() {
      mOrdRank++;
      return this;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrdState updateOrdParent() {
      if (mOrdRank > 0) {
        mOrdRank--;
        return this;
      } else {
        return OrdState.UNORD;
      }
    }
  },

  /** State of the HiddersMichiels - automaton. */
  UNORD;

  /**
   * If mOrderRank is 0, the result sequence will be in document order. If it is greater than 0 it
   * is not any more, but it can retain the ordered property, if a certain sequence of axis follows.
   * For more details see [Hidders, J., Michiels, P., "Avoiding Unnecessary Ordering Operations in
   * XPath", 2003]
   */
  static int mOrdRank;

  /**
   * Changes the state according to a child step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdChild() {
    mOrdRank++;
    return this;
  }

  /**
   * Changes the state according to a union step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdUnion() {
    return OrdState.UNORD;
  }

  /**
   * Changes the state according to a parent step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdParent() {
    return this;
  }

  /**
   * Changes the state according to a descendant/ descendant-or.self step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdDesc() {
    return OrdState.UNORD;
  }

  /**
   * Changes the state according to a following/preceding step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdFollPre() {
    return OrdState.UNORD;
  }

  /**
   * Changes the state according to a following-sibling/preceding-sibling step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdFollPreSib() {
    if (mOrdRank == 0) {
      mOrdRank++;
    }
    return this;
  }

  /**
   * Changes the state according to a ancestor step.
   * 
   * @return the updated order state
   */
  public OrdState updateOrdAncestor() {
    return OrdState.UNORD;
  }

  /**
   * Initializes the order state.
   */
  public void init() {
    mOrdRank = 0;

  }
}