metaquerytranslator.java

数字图书馆的互操作接口

package dli2fe.helpers;

/**
 * Title:        Digial Library Interoperable Interface Fudan Edition
 * Description:  This project contains all the classes required for DLI2FE interface. Developers use these classes to implement the wrapper and client side codes. The basic functions of DLI2FE is as follows:
 * Search: Search a digital library source site.
 * Metadata: Fetch metadata for a site.
 * ResultAccess: Get results for a given query.
 * DLI2FE uses Dublin Core as the basic attribute model, DAV/DASL as the general XML-based query language and CORBA as distributed object transportation mechanism.
 * Copyright:    Copyright (c) 2001
 * Company:      Fudan University
 * @author Carl Tao
 * @version 1.0
 */
import org.w3c.dom.*;
import dli2fe.xml.XMLObject;
import dli2fe.DLI2FEException;
import dli2fe.xml.DOMUtil;
import dli2fe.sample.MultimediaMeta;
import java.util.Hashtable;
import dli2fe.DAV;

public class MetaQueryTranslator {

  String sfwQuery;          // select/from/where query
  String select;
  boolean returnImage;
  String where;
  Hashtable attrTrans;


  public MetaQueryTranslator(XMLObject metaQuery, Hashtable transTable, XMLObject propList, String fromClause, String dummyAttr) throws DLI2FEException {
    Element elWhere;

    returnImage = false;
    select = "";
    where = "";
    sfwQuery = "";
    attrTrans = transTable;                   // make translation table globally accessable to other routines
    parsePropList(propList);                // parse select clause with translation

    if (metaQuery == null || (elWhere = DOMUtil.getChild(metaQuery.getElement(), DAV.where))==null) {
      if ("".equals(select))
        sfwQuery = "select " + dummyAttr +" from " + fromClause;
      else
        sfwQuery = "select " + select +" from " + fromClause;
      return;
    }

    parseQueryTree(elWhere);                // parse where clause with translation
    if ("".equals(select))
      sfwQuery = "select " + dummyAttr + " from " + fromClause + (("".equals(where)) ? "" : " where " + where);
    else
      sfwQuery = "select " + select + " from " + fromClause + (("".equals(where)) ? "" : " where " + where);
  }

  public String getMetaQuery() {
    return sfwQuery;
  }

  public String getSelectClause() {
    return select;
  }

  public boolean returnImage() {
    return returnImage;
  }

  public String getWhereClause() {
    return where;
  }

  void parseQueryTree(Element root) throws DLI2FEException {
    if (root == null)
      return;
    if (DAV.where.equals(root.getLocalName()))
      parseQueryTree(DOMUtil.getChild(root, "*"));
    if (DAV.and.equals(root.getLocalName()) || DAV.or.equals(root.getLocalName())) {
      boolean hasBrackets = true;
      if (DAV.where.equals(root.getParentNode().getLocalName()))
        hasBrackets = false;
      Node child = DOMUtil.getChild(root, "*");
      if (child == null)
        return;
      if (hasBrackets)
        where += "(";
      parseQueryTree((Element)child);
      while ((child = child.getNextSibling())!=null) {
        if (child.getNodeType()!=Node.ELEMENT_NODE)
          continue;
        where += " " + root.getLocalName() + " ";
        parseQueryTree((Element)child);
      }
      if (hasBrackets)
        where += ")";
    }
    if (DAV.not.equals(root.getLocalName())) {
      Element child = DOMUtil.getChild(root, "*");
      if (child == null)
        return;
      where += "(" + DAV.not + " ";
      parseQueryTree(child);
      where += ")";
    }
    if (DAV.eq.equals(root.getLocalName()) || DAV.like.equals(root.getLocalName())) {
      Element prop = DOMUtil.getDescendant(root, DAV.prop);
      Element literal = DOMUtil.getDescendant(root, DAV.literal);
      if (prop == null || literal == null)
        throw new DLI2FEException(DLI2FEException.BAD_QUERY_EXC, "No property or value specified in the meta query.");
      String propName = getAttrTranslation(DOMUtil.getDescendant(prop, "*").getLocalName());
      String literalValue = DOMUtil.getText(literal);
      literalValue = literalValue == null ? "" : literalValue;
      where += propName + "='" + literalValue +"'";
    }
  }

  void parsePropList(XMLObject propList) {
    NodeList nodes = propList.getElement().getElementsByTagName("*");
    for (int i = 0; i < nodes.getLength(); i++) {
      Node propNode = nodes.item(i);
      if ("prop".equals(nodes.item(i).getLocalName()))
        propNode = nodes.item(i).getFirstChild();
      if (!MultimediaMeta.Namespace.equals(propNode.getNamespaceURI())) {
        select += getAttrTranslation(propNode.getLocalName()) + ", ";
      } else
        returnImage = true;
    }
    if (select.endsWith(", "))
      select = select.substring(0, select.length()-2);
  }

  String getAttrTranslation(String inputAttr) {
    String outputAttr = (String)attrTrans.get(inputAttr);
    if (outputAttr == null)
      return inputAttr;
    return outputAttr;
  }

  public static void main(String[] args) {
    try {
      XMLObject query = new XMLObject("<?xml version='1.0' encoding='GB2312' ?> <basicsearch xmlns='http://www.cs.fudan.edu.cn/DLI2FE/1.0#' xmlns:ts='http://cs.fudan.edu.cn/travel/#' xmlns:mm='http://www.cs.fudan.edu.cn/multimedia/#'>  <where> <and> <or> <eq> <prop><ts:Location.Province/></prop> <literal>河北</literal> </eq> <eq> <prop><ts:Location.Province/></prop> <literal>山西</literal> </eq> </or> <eq> <prop><Scene.Culture.Figures.Figure/></prop> <literal>廉颇</literal> </eq> </and> </where> </basicsearch>");
//            XMLObject query = new XMLObject("<?xml version='1.0' encoding='GB2312' ?> <basicsearch xmlns='http://www.cs.fudan.edu.cn/DLI2FE/1.0#' xmlns:ts='http://cs.fudan.edu.cn/travel/#' xmlns:mm='http://www.cs.fudan.edu.cn/multimedia/#'>  <where> <like><prop><mm:image/></prop><literal>http://aaa/</literal> </like> </where> </basicsearch>");
      Hashtable attrTransTable = new Hashtable();
      attrTransTable.put("Location.Province", "Scene.Location.Province");
      XMLObject propList = new XMLObject("<?xml version='1.0' encoding='GB2312' ?> <proplist xmlns='http://www.cs.fudan.edu.cn/DLI2FE/1.0#' xmlns:ts='http://cs.fudan.edu.cn/travel/#' xmlns:mm='http://www.cs.fudan.edu.cn/multimedia/#'>    <ts:Scene.Name/><ts:Scene.SubSights.SubSight/>        </proplist> ");//<ts:Scene.Name/>  <ts:Location.Province/>
      MetaQueryTranslator mqtran = new MetaQueryTranslator(query, attrTransTable, propList, "Sight", "Scene.Name");
      System.out.println(mqtran.getMetaQuery());
      System.out.print("Return image? " + mqtran.returnImage());
    } catch (DLI2FEException ex) {
      System.out.println(ex);
    }
  }
}