io.sirix.service.xml.xpath.ExpressionSingle Maven / Gradle / Ivy
/**
* 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,
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* 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);
}
}