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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;

import io.sirix.api.Axis;
import io.sirix.service.xml.xpath.expr.UnionAxis;
import io.sirix.service.xml.xpath.filter.DupFilterAxis;
import io.sirix.axis.AncestorAxis;
import io.sirix.axis.ChildAxis;
import io.sirix.axis.DescendantAxis;
import io.sirix.axis.FollowingAxis;
import io.sirix.axis.FollowingSiblingAxis;
import io.sirix.axis.NestedAxis;
import io.sirix.axis.ParentAxis;
import io.sirix.axis.PrecedingAxis;
import io.sirix.axis.PrecedingSiblingAxis;
import io.sirix.axis.filter.FilterAxis;

/**
 * 

* This class builds an execution chain to execute a XPath query. All added axis are build together * by using NestedAxis. */ public class ExpressionSingle { /** * Counts the number of added axis. This is used to handle the special behavior for the first and * second axis that are added. */ private int mNumber; /** The first added axis has to be stored till a second one is added. */ private Axis mFirstAxis; /** Contains the execution chain consisting of nested NestedAxis. */ private Axis mExpr; /** Current ordering state. */ private OrdState mOrd; /** Current duplicate state. */ private DupState mDup; /** * Constructor. Initializes the internal state. */ public ExpressionSingle() { mNumber = 0; mOrd = OrdState.MAX1; mOrd.init(); mDup = DupState.MAX1; } /** * Adds a new Axis to the expression chain. The first axis that is added has to be stored till a * second axis is added. When the second axis is added, it is nested with the first one and builds * the execution chain. * * @param pAx the axis to add */ public void add(final Axis pAx) { Axis axis = pAx; if (isDupOrd(axis)) { axis = new DupFilterAxis(axis.asXmlNodeReadTrx(), axis); DupState.nodup = true; } switch (mNumber) { case 0: mFirstAxis = axis; mNumber++; break; case 1: mExpr = new NestedAxis(mFirstAxis, axis); mNumber++; break; default: final Axis cache = mExpr; mExpr = new NestedAxis(cache, axis); } } /** * Returns a chain to execute the query. If there is only one axis added, the chain was not build * yet, so only this axis is returned. * * @return The query execution chain */ public Axis getExpr() { return (mNumber == 1) ? mFirstAxis : mExpr; } /** * Returns the number of axis in this expression. * * @return size of the expression */ public int getSize() { return mNumber; } /** * Determines for a given string representation of an axis, whether this axis leads to duplicates * in the result sequence or not. Furthermore it determines the new state for the order state that * specifies, if the result sequence is in document order. This method is implemented according to * the automata in [Hidders, J., Michiels, P., "Avoiding Unnecessary Ordering Operations in * XPath", 2003] * * @param ax name of the current axis * @return true, if expression is still duplicate free */ public boolean isDupOrd(final Axis ax) { Axis axis = ax; while (axis instanceof FilterAxis) { axis = ((FilterAxis) axis).getAxis(); } if (axis instanceof UnionAxis) { mOrd = mOrd.updateOrdUnion(); mDup = mDup.updateUnion(); } else if (axis instanceof ChildAxis) { mOrd = mOrd.updateOrdChild(); mDup = mDup.updateDupChild(); } else if (axis instanceof ParentAxis) { mOrd = mOrd.updateOrdParent(); mDup = mDup.updateDupParent(); } else if (axis instanceof DescendantAxis) { mOrd = mOrd.updateOrdDesc(); mDup = mDup.updateDupDesc(); } else if (axis instanceof AncestorAxis) { mOrd = mOrd.updateOrdAncestor(); mDup = mDup.updateDupAncestor(); } else if (axis instanceof FollowingAxis || axis instanceof PrecedingAxis) { mOrd = mOrd.updateOrdFollPre(); mDup = mDup.updateDupFollPre(); } else if (axis instanceof FollowingSiblingAxis || axis instanceof PrecedingSiblingAxis) { mOrd = mOrd.updateOrdFollPreSib(); mDup = mDup.updateDupFollPreSib(); } return !DupState.nodup; } /** * @return true, if the result is in document order */ public boolean isOrdered() { // the result sequence is unordered, if the order rank is greater than // zero // or the order state is in state UNORD // return (ord != OrdState.UNORD && ord.mOrdRank == 0); return (mOrd != OrdState.UNORD && OrdState.mOrdRank == 0); } }





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