Metacat

/**

 *  '$RCSfile$'

 *    Purpose: A Class that represents a structured query, and can be 

 *             constructed from an XML serialization conforming to 

 *             pathquery.dtd. The printSQL() method can be used to print 

 *             a SQL serialization of the query.

 *  Copyright: 2000 Regents of the University of California and the

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Matt Jones

 *    Release: @release@

 *

 *   '$Author: bojilova $'

 *     '$Date: 2001-07-17 09:20:02 -0700 (Tue, 17 Jul 2001) $'

 * '$Revision: 795 $'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.metacat;

import java.io.*;

import java.util.Stack;

import java.util.Vector;

import java.util.Enumeration;

import org.xml.sax.Attributes;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

import org.xml.sax.SAXParseException;

import org.xml.sax.XMLReader;

import org.xml.sax.helpers.XMLReaderFactory;

import org.xml.sax.helpers.DefaultHandler;

/**

 * A Class that represents a structured query, and can be 

 * constructed from an XML serialization conforming to @see pathquery.dtd. 

 * The printSQL() method can be used to print a SQL serialization of the query.

 */

public class QuerySpecification extends DefaultHandler {

  /** flag determining whether extended query terms are present */

  private boolean containsExtendedSQL=false;

  /** Identifier for this query document */

  private String meta_file_id;

  /** Title of this query */

  private String queryTitle;

  /** List of document types to be returned using package back tracing */

  private Vector returnDocList;

  /** List of document types to be searched */

  private Vector filterDocList;

  /** List of fields to be returned in result set */

  private Vector returnFieldList;

  /** List of users owning documents to be searched */

  private Vector ownerList;

  /** List of sites/scopes used to constrain search */

  private Vector siteList;

  /** The root query group that contains the recursive query constraints */

  private QueryGroup query = null;

  // Query data structures used temporarily during XML parsing

  private Stack elementStack;

  private Stack queryStack;

  private String currentValue;

  private String currentPathexpr;

  private String parserName = null;

  private String accNumberSeparator = null;

  /**

   * construct an instance of the QuerySpecification class 

   *

   * @param queryspec the XML representation of the query (should conform

   *                  to pathquery.dtd) as a Reader

   * @param parserName the fully qualified name of a Java Class implementing

   *                  the org.xml.sax.XMLReader interface

   */

  public QuerySpecification( Reader queryspec, String parserName,

         String accNumberSeparator ) throws IOException {

    super();

    // Initialize the class variables

    returnDocList = new Vector();

    filterDocList = new Vector();

    elementStack = new Stack();

    queryStack   = new Stack();

    returnFieldList = new Vector();

    ownerList = new Vector();

    siteList = new Vector();

    this.parserName = parserName;

    this.accNumberSeparator = accNumberSeparator;

    // Initialize the parser and read the queryspec

    XMLReader parser = initializeParser();

    if (parser == null) {

      System.err.println("SAX parser not instantiated properly.");

    }

    try {

      parser.parse(new InputSource(queryspec));

    } catch (SAXException e) {

      System.err.println("error parsing data in " + 

                         "QuerySpecification.QuerySpecification");

      System.err.println(e.getMessage());

    }

  }

  /**

   * construct an instance of the QuerySpecification class 

   *

   * @param queryspec the XML representation of the query (should conform

   *                  to pathquery.dtd) as a String

   * @param parserName the fully qualified name of a Java Class implementing

   *                  the org.xml.sax.Parser interface

   */

  public QuerySpecification( String queryspec, String parserName,

         String accNumberSeparator) throws IOException {

    this(new StringReader(queryspec), parserName, accNumberSeparator);

  }

  /** Main routine for testing */

  static public void main(String[] args) {

     if (args.length < 1) {

       System.err.println("Wrong number of arguments!!!");

       System.err.println("USAGE: java QuerySpecification <xmlfile>");

       return;

     } else {

       int i = 0;

       boolean useXMLIndex = true;

       if ( args[i].equals( "-noindex" ) ) {

         useXMLIndex = false;

         i++;

       }

       String xmlfile  = args[i];

       try {

         MetaCatUtil util = new MetaCatUtil();

         FileReader xml = new FileReader(new File(xmlfile));

         QuerySpecification qspec = 

                 new QuerySpecification(xml, util.getOption("saxparser"),

                                        util.getOption("accNumberSeparator"));

         System.out.println(qspec.printSQL(useXMLIndex));

       } catch (IOException e) {

         System.err.println(e.getMessage());

       }

     }

  }

  /**

   * Returns true if the parsed query contains and extended xml query 

   * (i.e. there is at least one <returnfield> in the pathquery document)

   */

  public boolean containsExtendedSQL()

  {

    if(containsExtendedSQL)

    {

      return true;

    }

    else

    {

      return false;

    }

  }

  /**

   * Accessor method to return the identifier of this Query

   */

  public String getIdentifier()

  {

    return meta_file_id;

  }

  /**

   * method to set the identifier of this query

   */

  public void setIdentifier(String id) {

    this.meta_file_id = id;

  }

  /**

   * Accessor method to return the title of this Query

   */

  public String getQueryTitle()

  {

    return queryTitle;

  }

  /**

   * method to set the title of this query

   */

  public void setQueryTitle(String title)

  {

    this.queryTitle = title;

  }

  /**

   * Accessor method to return a vector of the return document types as

   * defined in the <returndoctype> tag in the pathquery dtd.

   */

  public Vector getReturnDocList()

  {

    return this.returnDocList;

  }

  /**

   * method to set the list of return docs of this query

   */

  public void setReturnDocList(Vector returnDocList)

  {

    this.returnDocList = returnDocList;

  }

  /**

   * Accessor method to return a vector of the filter doc types as

   * defined in the <filterdoctype> tag in the pathquery dtd.

   */

  public Vector getFilterDocList()

  {

    return this.filterDocList;

  }

  /**

   * method to set the list of filter docs of this query

   */

  public void setFilterDocList(Vector filterDocList)

  {

    this.filterDocList = filterDocList;

  }

  /**

   * Accessor method to return a vector of the extended return fields as

   * defined in the <returnfield> tag in the pathquery dtd.

   */

  public Vector getReturnFieldList()

  {

    return this.returnFieldList; 

  }

  /**

   * method to set the list of fields to be returned by this query

   */

  public void setReturnFieldList(Vector returnFieldList)

  {

    this.returnFieldList = returnFieldList;

  }

  /**

   * Accessor method to return a vector of the owner fields as

   * defined in the <owner> tag in the pathquery dtd.

   */

  public Vector getOwnerList()

  {

    return this.ownerList;

  }

  /**

   * method to set the list of owners used to constrain this query

   */

  public void setOwnerList(Vector ownerList)

  {

    this.ownerList = ownerList;

  }

  /**

   * Accessor method to return a vector of the site fields as

   * defined in the <site> tag in the pathquery dtd.

   */

  public Vector getSiteList()

  {

    return this.siteList;

  }

  /**

   * method to set the list of sites used to constrain this query

   */

  public void setSiteList(Vector siteList)

  {

    this.siteList = siteList;

  }

  /**

   * get the QueryGroup used to express query constraints

   */

  public QueryGroup getQueryGroup()

  {

    return query;

  }

  /**

   * Set up the SAX parser for reading the XML serialized query

   */

  private XMLReader initializeParser() {

    XMLReader parser = null;

    // Set up the SAX document handlers for parsing

    try {

      // Get an instance of the parser

      parser = XMLReaderFactory.createXMLReader(parserName);

      // Set the ContentHandler to this instance

      parser.setContentHandler(this);

      // Set the error Handler to this instance

      parser.setErrorHandler(this);

    } catch (Exception e) {

       System.err.println("Error in QuerySpcecification.initializeParser " + 

                           e.toString());

    }

    return parser;

  }

  /**

   * callback method used by the SAX Parser when the start tag of an 

   * element is detected. Used in this context to parse and store

   * the query information in class variables.

   */

  public void startElement (String uri, String localName, 

                            String qName, Attributes atts) 

         throws SAXException {

    BasicNode currentNode = new BasicNode(localName);

    // add attributes to BasicNode here

    if (atts != null) {

      int len = atts.getLength();

      for (int i = 0; i < len; i++) {

        currentNode.setAttribute(atts.getLocalName(i), atts.getValue(i));

      }

    }

    elementStack.push(currentNode); 

    if (currentNode.getTagName().equals("querygroup")) {

      QueryGroup currentGroup = new QueryGroup(

                                currentNode.getAttribute("operator"));

      if (query == null) {

        query = currentGroup;

      } else {

        QueryGroup parentGroup = (QueryGroup)queryStack.peek();

        parentGroup.addChild(currentGroup);

      }

      queryStack.push(currentGroup);

    }

  }

  /**

   * callback method used by the SAX Parser when the end tag of an 

   * element is detected. Used in this context to parse and store

   * the query information in class variables.

   */

  public void endElement (String uri, String localName,

                          String qName) throws SAXException {

    BasicNode leaving = (BasicNode)elementStack.pop(); 

    if (leaving.getTagName().equals("queryterm")) {

      boolean isCaseSensitive = (new Boolean(

              leaving.getAttribute("casesensitive"))).booleanValue();

      QueryTerm currentTerm = null;

      if (currentPathexpr == null) {

        currentTerm = new QueryTerm(isCaseSensitive,

                      leaving.getAttribute("searchmode"),currentValue);

      } else {

        currentTerm = new QueryTerm(isCaseSensitive,

                      leaving.getAttribute("searchmode"),currentValue,

                      currentPathexpr);

      }

      QueryGroup currentGroup = (QueryGroup)queryStack.peek();

      currentGroup.addChild(currentTerm);

      currentValue = null;

      currentPathexpr = null;

    } else if (leaving.getTagName().equals("querygroup")) {

      QueryGroup leavingGroup = (QueryGroup)queryStack.pop();

    }

  }

  /**

   * callback method used by the SAX Parser when the text sequences of an 

   * xml stream are detected. Used in this context to parse and store

   * the query information in class variables.

   */

  public void characters(char ch[], int start, int length) {

    String inputString = new String(ch, start, length);

    BasicNode currentNode = (BasicNode)elementStack.peek(); 

    String currentTag = currentNode.getTagName();

    if (currentTag.equals("meta_file_id")) {

      meta_file_id = inputString;

    } else if (currentTag.equals("querytitle")) {

      queryTitle = inputString;

    } else if (currentTag.equals("value")) {

      currentValue = inputString;

    } else if (currentTag.equals("pathexpr")) {

      currentPathexpr = inputString;

    } else if (currentTag.equals("returndoctype")) {

      returnDocList.add(inputString);

    } else if (currentTag.equals("filterdoctype")) {

      filterDocList.add(inputString);

    } else if (currentTag.equals("returnfield")) {

      returnFieldList.add(inputString);

      containsExtendedSQL = true;

    } else if (currentTag.equals("filterdoctype")) {

      filterDocList.add(inputString);

    } else if (currentTag.equals("owner")) {

      ownerList.add(inputString);

    } else if (currentTag.equals("site")) {

      siteList.add(inputString);

    }

  }

  /**

   * create a SQL serialization of the query that this instance represents

   */

  public String printSQL(boolean useXMLIndex) {

    StringBuffer self = new StringBuffer();

    self.append("SELECT docid,docname,doctype,");

    self.append("date_created, date_updated, rev ");

    self.append("FROM xml_documents WHERE docid IN (");

    // This determines the documents that meet the query conditions

    self.append(query.printSQL(useXMLIndex));

    self.append(") ");

    // Add SQL to filter for doctypes requested in the query

    // This is an implicit OR for the list of doctypes. Only doctypes in this

    // list will be searched if the tag is present

    if (!filterDocList.isEmpty()) {

      boolean firstdoctype = true;

      self.append(" AND ("); 

      Enumeration en = filterDocList.elements();

      while (en.hasMoreElements()) {

        String currentDoctype = (String)en.nextElement();

        if (firstdoctype) {

           firstdoctype = false;

           self.append(" doctype = '" + currentDoctype + "'"); 

        } else {

          self.append(" OR doctype = '" + currentDoctype + "'"); 

        }

      }

      self.append(") ");

    }

    // Add SQL to filter for owners requested in the query

    // This is an implicit OR for the list of owners

    if (!ownerList.isEmpty()) {

      boolean first = true;

      self.append(" AND ("); 

      Enumeration en = ownerList.elements();

      while (en.hasMoreElements()) {

        String current = (String)en.nextElement();

        if (first) {

           first = false;

           self.append(" user_owner = '" + current + "'"); 

        } else {

          self.append(" OR user_owner = '" + current + "'"); 

        }

      }

      self.append(") ");

    }

    // Add SQL to filter for sites requested in the query

    // This is an implicit OR for the list of sites

    if (!siteList.isEmpty()) {

      boolean first = true;

      self.append(" AND ("); 

      Enumeration en = siteList.elements();

      while (en.hasMoreElements()) {

        String current = (String)en.nextElement();

        if (first) {

           first = false;

           self.append(" SUBSTR(docid, 1, INSTR(docid, '" +

               accNumberSeparator + "')-1) = '" + current + "'"); 

        } else {

          self.append(" OR SUBSTR(docid, 1, INSTR(docid, '" +

               accNumberSeparator + "')-1) = '" + current + "'"); 

        }

      }

      self.append(") ");

    }

    //System.out.println(self.toString());

    return self.toString();

  }

  /**

   * This method prints sql based upon the <returnfield> tag in the

   * pathquery document.  This allows for customization of the 

   * returned fields

   * @param doclist the list of document ids to search by

   */

  public String printExtendedSQL(String doclist)

  {  

    StringBuffer self = new StringBuffer();

    self.append("select xml_nodes.docid, xml_index.path, xml_nodes.nodedata ");

    self.append("from xml_index, xml_nodes where xml_index.nodeid=");

    self.append("xml_nodes.parentnodeid and (xml_index.path like '");

    boolean firstfield = true;

    //put the returnfields into the query

    //the for loop allows for multiple fields

    for(int i=0; i<returnFieldList.size(); i++)

    {

      if(firstfield)

      {

        firstfield = false;

        self.append((String)returnFieldList.elementAt(i));

        self.append("' ");

      }

      else

      {

        self.append("or xml_index.path like '");

        self.append((String)returnFieldList.elementAt(i));

        self.append("' ");

      }

    }

    self.append(") AND xml_nodes.docid in (");

    //self.append(query.printSQL());

    self.append(doclist);

    self.append(")");

    self.append(" AND xml_nodes.nodetype = 'TEXT'");

    //System.out.println(self.toString());

    return self.toString();

  }

  public static String printRelationSQL(String docid)

  {

    StringBuffer self = new StringBuffer();

    self.append("select subject, relationship, object, subdoctype, ");

    self.append("objdoctype from xml_relation ");

    self.append("where docid like '").append(docid).append("'");

    return self.toString();

  }

  /**

   * Prints sql that returns all relations in the database.

   */

  public static String printPackageSQL()

  {

    StringBuffer self = new StringBuffer();

    self.append("select z.nodedata, x.nodedata, y.nodedata from ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/subject') s, (select nodeid, parentnodeid ");

    self.append("from xml_index where path like ");

    self.append("'triple/relationship') rel, ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/object') o, ");

    self.append("xml_nodes x, xml_nodes y, xml_nodes z ");

    self.append("where s.parentnodeid = rel.parentnodeid ");

    self.append("and rel.parentnodeid = o.parentnodeid ");

    self.append("and x.parentnodeid in rel.nodeid ");

    self.append("and y.parentnodeid in o.nodeid ");

    self.append("and z.parentnodeid in s.nodeid ");

    //self.append("and z.nodedata like '%");

    //self.append(docid);

    //self.append("%'");

    return self.toString();

  }

  /**

   * Prints sql that returns all relations in the database that were input

   * under a specific docid

   * @param docid the docid to search for.

   */

  public static String printPackageSQL(String docid)

  {

    StringBuffer self = new StringBuffer();

    self.append("select z.nodedata, x.nodedata, y.nodedata from ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/subject') s, (select nodeid, parentnodeid ");

    self.append("from xml_index where path like ");

    self.append("'triple/relationship') rel, ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/object') o, ");

    self.append("xml_nodes x, xml_nodes y, xml_nodes z ");

    self.append("where s.parentnodeid = rel.parentnodeid ");

    self.append("and rel.parentnodeid = o.parentnodeid ");

    self.append("and x.parentnodeid in rel.nodeid ");

    self.append("and y.parentnodeid in o.nodeid ");

    self.append("and z.parentnodeid in s.nodeid ");

    self.append("and z.docid like '").append(docid).append("'");

    return self.toString();

  }

  /**

   * Returns all of the relations that has a certain docid in the subject

   * or the object.

   * 

   * @param docid the docid to search for

   */

  public static String printPackageSQL(String subDocidURL, String objDocidURL)

  {

    StringBuffer self = new StringBuffer();

    self.append("select z.nodedata, x.nodedata, y.nodedata from ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/subject') s, (select nodeid, parentnodeid ");

    self.append("from xml_index where path like ");

    self.append("'triple/relationship') rel, ");

    self.append("(select nodeid, parentnodeid from xml_index where path like ");

    self.append("'triple/object') o, ");

    self.append("xml_nodes x, xml_nodes y, xml_nodes z ");

    self.append("where s.parentnodeid = rel.parentnodeid ");

    self.append("and rel.parentnodeid = o.parentnodeid ");

    self.append("and x.parentnodeid in rel.nodeid ");

    self.append("and y.parentnodeid in o.nodeid ");

    self.append("and z.parentnodeid in s.nodeid ");

    self.append("and (z.nodedata like '");

    self.append(subDocidURL);

    self.append("' or y.nodedata like '");

    self.append(objDocidURL);

    self.append("')");

    return self.toString();

  }

  public static String printGetDocByDoctypeSQL(String docid)

  {

    StringBuffer self = new StringBuffer();

    self.append("SELECT docid,docname,doctype,");

    self.append("date_created, date_updated ");

    self.append("FROM xml_documents WHERE docid IN (");

    self.append(docid).append(")");

    return self.toString();

  }

  /**

   * create a String description of the query that this instance represents.

   * This should become a way to get the XML serialization of the query.

   */

  public String toString() {

    return "meta_file_id=" + meta_file_id + "\n" + query;

//DOCTITLE attr cleared from the db

//    return "meta_file_id=" + meta_file_id + "\n" + 

//           "querytitle=" + querytitle + "\n" + query;

  }

  /** a utility class that represents a group of terms in a query */

  private class QueryGroup {

    private String operator = null;  // indicates how query terms are combined

    private Vector children = null;  // the list of query terms and groups

    /** 

     * construct a new QueryGroup 

     *

     * @param operator the boolean conector used to connect query terms 

     *                    in this query group

     */

    public QueryGroup(String operator) {

      this.operator = operator;

      children = new Vector();

    }

    /** 

     * Add a child QueryGroup to this QueryGroup

     *

     * @param qgroup the query group to be added to the list of terms

     */

    public void addChild(QueryGroup qgroup) {

      children.add((Object)qgroup); 

    }

    /**

     * Add a child QueryTerm to this QueryGroup

     *

     * @param qterm the query term to be added to the list of terms

     */

    public void addChild(QueryTerm qterm) {

      children.add((Object)qterm); 

    }

    /**

     * Retrieve an Enumeration of query terms for this QueryGroup

     */

    public Enumeration getChildren() {

      return children.elements();

    }

    /**

     * create a SQL serialization of the query that this instance represents

     */

    public String printSQL(boolean useXMLIndex) {

      StringBuffer self = new StringBuffer();

      boolean first = true;

      self.append("(");

      Enumeration en= getChildren();

      while (en.hasMoreElements()) {

        Object qobject = en.nextElement();

        if (first) {

          first = false;

        } else {

          self.append(" " + operator + " ");

        }

        if (qobject instanceof QueryGroup) {

          QueryGroup qg = (QueryGroup)qobject;

          self.append(qg.printSQL(useXMLIndex));

        } else if (qobject instanceof QueryTerm) {

          QueryTerm qt = (QueryTerm)qobject;

          self.append(qt.printSQL(useXMLIndex));

        } else {

          System.err.println("qobject wrong type: fatal error");

        }

      }

      self.append(") \n");

      return self.toString();

    }

    /**

     * create a String description of the query that this instance represents.

     * This should become a way to get the XML serialization of the query.

     */

    public String toString() {

      StringBuffer self = new StringBuffer();

      self.append("  (Query group operator=" + operator + "\n");

      Enumeration en= getChildren();

      while (en.hasMoreElements()) {

        Object qobject = en.nextElement();

        self.append(qobject);

      }

      self.append("  )\n");

      return self.toString();

    }

  }

  /** a utility class that represents a single term in a query */

  private class QueryTerm {

    private boolean casesensitive = false;

    private String searchmode = null;

    private String value = null;

    private String pathexpr = null;

    /**

     * Construct a new instance of a query term for a free text search

     * (using the value only)

     *

     * @param casesensitive flag indicating whether case is used to match

     * @param searchmode determines what kind of substring match is performed

     *        (one of starts-with|ends-with|contains|matches-exactly)

     * @param value the text value to match

     */

    public QueryTerm(boolean casesensitive, String searchmode, 

                     String value) {

      this.casesensitive = casesensitive;

      this.searchmode = searchmode;

      this.value = value;

    }

    /**

     * Construct a new instance of a query term for a structured search

     * (matching the value only for those nodes in the pathexpr)

     *

     * @param casesensitive flag indicating whether case is used to match

     * @param searchmode determines what kind of substring match is performed

     *        (one of starts-with|ends-with|contains|matches-exactly)

     * @param value the text value to match

     * @param pathexpr the hierarchical path to the nodes to be searched

     */

    public QueryTerm(boolean casesensitive, String searchmode, 

                     String value, String pathexpr) {

      this(casesensitive, searchmode, value);

      this.pathexpr = pathexpr;

    }

    /** determine if the QueryTerm is case sensitive */

    public boolean isCaseSensitive() {

      return casesensitive;

    }

    /** get the searchmode parameter */

    public String getSearchMode() {

      return searchmode;

    }

    /** get the Value parameter */

    public String getValue() {

      return value;

    }

    /** get the path expression parameter */

    public String getPathExpression() {

      return pathexpr;

    }

    /**

     * create a SQL serialization of the query that this instance represents

     */

    public String printSQL(boolean useXMLIndex) {

      StringBuffer self = new StringBuffer();

      // Uppercase the search string if case match is not important

      String casevalue = null;

      String nodedataterm = null;

      if (casesensitive) {

        nodedataterm = "nodedata";

        casevalue = value;

      } else {

        nodedataterm = "UPPER(nodedata)";

        casevalue = value.toUpperCase();

      }

      // Add appropriate wildcards to search string

      //String searchvalue = null;

      String searchexpr = null;

      if (searchmode.equals("starts-with")) {

        //searchvalue = casevalue + "%";

        searchexpr = nodedataterm + " LIKE '" + casevalue + "%' ";

      } else if (searchmode.equals("ends-with")) {

        //searchvalue = "%" + casevalue;

        searchexpr = nodedataterm + " LIKE '%" + casevalue + "' ";

      } else if (searchmode.equals("contains")) {

        //searchvalue = "%" + casevalue + "%";

        searchexpr = nodedataterm + " LIKE '%" + casevalue + "%' ";

      } else if (searchmode.equals("equals")) {

        //searchvalue = casevalue;

        searchexpr = nodedataterm + " = '" + casevalue + "' ";

      } else if (searchmode.equals("isnot-equal")) {

        //searchvalue = casevalue;

        searchexpr = nodedataterm + " != '" + casevalue + "' ";

      } else { 

        //searchvalue = casevalue;

        String oper = null;

        if (searchmode.equals("greater-than")) {

          oper = ">";

        } else if (searchmode.equals("greater-than-equals")) {

          oper = ">=";

        } else if (searchmode.equals("less-than")) {

          oper = "<";

        } else if (searchmode.equals("less-than-equals")) {

          oper = "<=";

        } else {

          System.out.println("NOT expected case. NOT recognized operator: " +

                             searchmode);

          return null;

        }

        try {

          // it is number; numeric comparison

          searchexpr = nodedataterm + " " + oper + " " +

                       new Double(casevalue) + " ";          

        } catch (NumberFormatException nfe) {

          // these are characters; character comparison

          searchexpr = nodedataterm + " " + oper + " '" + casevalue + "' ";

        }

      }

      self.append("SELECT DISTINCT docid FROM xml_nodes WHERE \n");

      //self.append(nodedataterm + " LIKE " + "'" + searchvalue + "' ");

      self.append(searchexpr);

      if (pathexpr != null) {

        self.append("AND parentnodeid IN ");

        // use XML Index

        if ( useXMLIndex ) {

          self.append("(SELECT nodeid FROM xml_index WHERE path LIKE " + 

                      "'" +  pathexpr + "') " );

        // without using XML Index; using nested statements instead

        } else {

          self.append(useNestedStatements(pathexpr));

        }

      }

      return self.toString();

    }

    /* 

     * Constraint the query with @pathexp without using the XML Index,

     * but nested SQL statements instead. The query migth be slower.

     */

    private String useNestedStatements(String pathexpr)

    {

      StringBuffer nestedStmts = new StringBuffer();

      Vector nodes = new Vector();

      String path = pathexpr;

      int inx = 0;

      do {

        inx = path.lastIndexOf("/");

//System.out.println(path.substring(inx+1));

        nodes.addElement(path.substring(inx+1));

        path = path.substring(0, Math.abs(inx));

      } while ( inx > 0 );

      // nested statements

      int i = 0;

      for (i = 0; i < nodes.size()-1; i++) {

        nestedStmts.append("(SELECT nodeid FROM xml_nodes" + 

                           " WHERE nodename LIKE '" +

                             (String)nodes.elementAt(i) + "'" +

                           " AND parentnodeid IN ");

      }

      // for the last statement: it is without " AND parentnodeid IN "

      nestedStmts.append("(SELECT nodeid FROM xml_nodes" + 

                         " WHERE nodename LIKE '" +

                         (String)nodes.elementAt(i) + "'" );

      // node.size() number of closing brackets

      for (i = 0; i < nodes.size(); i++) {

        nestedStmts.append(")");

      }

//System.out.println(nestedStmts.toString());

      return nestedStmts.toString();

    }

    /**

     * create a String description of the query that this instance represents.

     * This should become a way to get the XML serialization of the query.

     */

    public String toString() {