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/*
 * Copyright (C) 1999-2004 <a href="mailto:mandarax@jbdietrich.com">Jens Dietrich</a>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */


package org.mandarax.rdf;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.*;
import org.apache.commons.collections.iterators.ArrayIterator;
import org.mandarax.kernel.*;
import org.mandarax.util.ClauseIterator;

/**
 * Clause set implementation to access RDF documents. 
 * <p>
 * A RDF document usually contains more than one predicate. However, the predicates must be known 
 * when adding the clause set to a knowledge base as the kb uses them for internal indexing (i.e. 
 * to support retrieval of knowledge for a certain predicate). There are two strategies how this can be achieved: 
 * <ol>
 * <li>Using the property <code>predicates</code>
 * <li>Gathering the predicates from the document. This is the default strategy, it happens when <code>getKey()</code>
 * is called (e.g., by the kb) and the predicates have not been initialized (lazy initialization). This can be customized
 * using the <code>maxFetchSize</code> property which constraints the max number of statements analyzed. 
 * <p>
 * TODO implement a strategy in the kb for clause sets to be used for arbitrary predicates.
 * <p>
 * The RDF is read from a URL. If the URL is a network URL (= not a local file), firewalls and proxies
 * must be configured correctly. Theer are various ways to accomplish this. 
 * E.g., one may include the following parameter on the java command line:
 * <p><code>-DsocksProxyHost=[your-proxy-domain-name-or-ip-address] </code> // for a socks proxy 
 * <br><code>-DproxySet=true -DproxyHost=[your-proxy] -DproxyPort=[your-proxy-port-number] </code> // for an http proxy
 * <p>
 * These properties can also be set programatically as follows:
 * <p><code>
 * <br>System.getProperties().put("proxySet","true");
 * <br>System.getProperties().put("proxyHost","proxy.hostname");
 * <br>System.getProperties().put("proxyPort",port_number);
 * </code> 
 * @author <A HREF="mailto:j.b.dietrich@massey.ac.nz">Jens Dietrich</A> <A HREF="mailto:paschke@in.tum.de">Adrian Paschke</A>
 * @version 1.1 <01 August 2004>
 * @since 0.1
 */

public class RDFClauseSet extends AbstractPropertiesSupport implements ClauseSet, RDFLogger, RDFConstants {

  private URL url = null;
  private String language = RDFXML;
  private Predicate[] predicates = null;
  int maxFetchSize = -1; // this means NO LIMIT
  /**
   * Empty constructor.
   * The url should be passed. This constructor is included to make this a POJO (plain old java object) 
   * and to support tools based on reflection.
   */
  public RDFClauseSet() {
    super();
  }
  /**
   * Constructor.
   * @param url the RDF model is loaded from this URL
   */
  public RDFClauseSet(URL url) {
    super();
    this.url = url;
  }

  /**
   * Constructor.
   * @param f a local file
   * @exception a MalformedURLException is thrown if the file cannot be converted into a URL
   */
  public RDFClauseSet(java.io.File f) throws MalformedURLException {
    super();
    this.url = f.toURL();
  }
  
    /**
     * Add a clause set listener.
     * @param l the listener
     */
    public void addClauseSetChangeListener(ClauseSetChangeListener l) {
      // TODO
    }

    /**
     * Get a key for indexing. The knowledge base is supposed to
     * contain only clauses having the same key object. 
     * @return array of RDFPredicate
     */
    public synchronized Object getKey()  {
      return predicates;
    }

    /**
     * Remove a clause set listener.
     * @param l the listener
     */
    public void removeClauseSetChangeListener(ClauseSetChangeListener l) {
      // TODO
    }
    /**
     * Get an iterator iterating over the predicates contained in this clause set.
     * @return an iterator
     */
    public Iterator predicates() {
      return new ArrayIterator(predicates);
    }

  /**
   * Return a clause iterator.
   * @return a clause iterator
   */
  public ClauseIterator clauses() throws ClauseSetException {
    return new RDFClauseIterator(url,language,null);
  }

  /**
   * Return a clause iterator.
   * @return a clause iterator
   * @param query the query clause
   * @param additionalParameter an optional additional parameter
   * @see org.mandarax.kernel.KnowledgeOwner#clauses(org.mandarax.kernel.Clause, java.lang.Object)
   */
  public ClauseIterator clauses(Clause query, Object additionalParameter) throws ClauseSetException {
    Object obj = query.getKey();
    if (obj==null || !(obj instanceof RDFPredicate)) throw new ClauseSetException("Cannot get clause iterator, rdf predicate expected instead of " + obj);
    return new RDFClauseIterator(url,language,(RDFPredicate)obj);
  }
  /**
   * Get the url.
   * @return the url
   */
    public URL getURL() {
      return url;
    }
  /**
   * Set the url.
   * @param url the url
   */
  public void setURL(URL url) {
    this.url = url;
  }
  /**
   * Convert this object to a string.
   * @return a string
   */
  public String toString() {
    return new StringBuffer()
      .append("aRDFClauseSet(")
      .append(this.url)
      .append(')')
      .toString();
  }
  /**
   * Get the max fetch size.
   * @return Returns the maxFetchSize.
   */
  public int getMaxFetchSize() {
    return maxFetchSize;
  }
  /**
   * Set the max fetch size.
   * @param maxFetchSize The maxFetchSize to set.
   */
  public void setMaxFetchSize(int maxFetchSize) {
    this.maxFetchSize = maxFetchSize;
  }
  /**
   * Get the predicates.
   * @return Returns the predicates.
   */
  public Predicate[] getPredicates() {
    return predicates;
  }
  /**
   * Set the predicates.
   * @param predicates The predicates to set.
   */
  public void setPredicates(Predicate[] predicates) {
    this.predicates = predicates;
  }
}
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