source: trunk/src/xmlpatterns/acceltree/qacceltree_p.h@ 98

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//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.

#ifndef Patternist_AccelTree_H
#define Patternist_AccelTree_H

#include <QHash>
#include <QUrl>
#include <QVector>
#include <QXmlName>

#include "qitem_p.h"
#include "qnamepool_p.h"

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

namespace QPatternist
{
    template<bool> class AccelTreeBuilder;

    /**
     * @short Stores an XML document using the XPath Accelerator scheme, also
     * known as pre/post numbering.
     *
     * Working on this code will be destructive without a proper understanding of
     * the Accelerator scheme, so do check out the links. We don't implement any form
     * of staircase join, although that is only due to time constraints.
     *
     * @author Frans Englich <[email protected]>
     * @see <a href="http://www.pathfinder-xquery.org/?q=research/xpath-accel">XPath
     * Accelerator</a>
     * @see <a href="http://www.pathfinder-xquery.org/files/xpath-accel.pdf">Accelerating
     * XPath Location Steps, Torsten Grust</a>
     * @see <a href="http://citeseer.ist.psu.edu/cache/papers/cs/29367/http:zSzzSzwww.informatik.uni-konstanz.dezSz~grustzSzfileszSzstaircase-join.pdf/grust03staircase.pdf">Staircase Join:
     * Teach a Relational DBMS to Watch its (Axis) Steps</a>
     * @see <a href="http://ftp.cwi.nl/CWIreports/INS/INS-E0510.pdf">Loop-lifted
     * staircase join: from XPath to XQuery, Torsten Grust</a>
     * @see <a href="http://englich.wordpress.com/2007/01/09/xmlstat/">xmlstat, Frans Englich</a>
     * @see <a href"http://www.inf.uni-konstanz.de/dbis/publications/download/accelerating-locsteps.pdf">Accelerating
     * XPath Evaluation in Any RDBMS, Torsten Grust</a>
     */
    class AccelTree : public QAbstractXmlNodeModel
    {
    public:
        using QAbstractXmlNodeModel::createIndex;

        typedef QExplicitlySharedDataPointer<AccelTree> Ptr;
        typedef qint32 PreNumber;
        typedef PreNumber PostNumber;
        typedef qint8 Depth;

        inline AccelTree(const QUrl &docURI,
                         const QUrl &bURI) : m_documentURI(docURI),
                                             m_baseURI(bURI)
        {
            /* Pre-allocate at least a little bit. */
            // TODO. Do it according to what an average 4 KB doc contains.
            basicData.reserve(100);
            data.reserve(30);
        }

        /**
         * @short Houses data for a node, and that all node kinds have.
         *
         * BasicNodeData is internal to the Accel tree implementation, and is
         * only used by those classes.
         *
         * @author Frans Englich <[email protected]>
         * @todo Can't m_kind be coded somewhere else? If m_name is invalid,
         * its bits can be used to distinguish the node types that doesn't have
         * names, and for elements, attributes and processing instructions, we need
         * two bits, somewhere. Attributes and processing instructions can't have a
         * size, is that of help? There's also certain rules for the names. For instance,
         * a processing instruction will never have a prefix nor namespace. Neither
         * will an attribute node have a default, non-empty namespace, right?
         * @todo Compress text nodes, add general support for it in Patternist.
         */
        class BasicNodeData
        {
        public:
            inline BasicNodeData()
            {
            }

            inline BasicNodeData(const PreNumber aDepth,
                                 const PreNumber aParent,
                                 const QXmlNodeModelIndex::NodeKind k,
                                 const PreNumber s,
                                 const QXmlName n = QXmlName()) : m_parent(aParent)
                                                                , m_size(s)
                                                                , m_name(n)
                                                                , m_depth(aDepth)
                                                                , m_kind(k)
            {
            }

            inline Depth depth() const
            {
                return m_depth;
            }

            inline PreNumber parent() const
            {
                return m_parent;
            }

            /**
             * @see AccelTree::size()
             */
            inline PreNumber size() const
            {
                /* Remember that we use the m_size to signal compression if
                 * we're a text node. */
                if(m_kind == QXmlNodeModelIndex::Text)
                    return 0;
                else
                    return m_size;
            }

            inline void setSize(const PreNumber aSize)
            {
                m_size = aSize;
            }

            inline QXmlNodeModelIndex::NodeKind kind() const
            {
                return m_kind;
            }

            inline QXmlName name() const
            {
                return m_name;
            }

            inline bool isCompressed() const
            {
                Q_ASSERT_X(m_kind == QXmlNodeModelIndex::Text, Q_FUNC_INFO,
                           "Currently, only text nodes are compressed.");
                /* Note, we don't call size() here, since it has logic for text
                 * nodes. */
                return m_size == IsCompressed;
            }

        private:
            /**