javaowl-commit

[Elmer G. <ega...@us...>]

Update of /cvsroot/javaowl/JavaOWL/src/org/javaowl/models/prevalence
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv18474/src/org/javaowl/models/prevalence

Modified Files:
	PrevalentGraph.java AddTripleCommand.java StorageGraph.java 
	DeleteTripleCommand.java 
Added Files:
	TripleUtil.java 
Removed Files:
	StorageUtil.java 
Log Message:
Changed serialization to externalization.

--- NEW FILE: TripleUtil.java ---
/*
 * (c) Copyright 2003, Hewlett-Packard Development Company, LP [See end of file]
 */

package org.javaowl.models.prevalence;

import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import com.hp.hpl.jena.datatypes.RDFDatatype;
import com.hp.hpl.jena.datatypes.TypeMapper;
import com.hp.hpl.jena.db.RDFRDBException;
import com.hp.hpl.jena.graph.Node;
import com.hp.hpl.jena.graph.Node_Literal;
import com.hp.hpl.jena.graph.Node_URI;
import com.hp.hpl.jena.graph.Node_Variable;
import com.hp.hpl.jena.graph.Triple;
import com.hp.hpl.jena.graph.impl.LiteralLabel;
import com.hp.hpl.jena.rdf.model.AnonId;

public class TripleUtil {

    /*
     * The following routines are responsible for encoding nodes as database
     * structures. For each node type stored (currently, literals, URI, blank),
     * there are two possible encodings depending on the node size. Small nodes
     * may be stored within a statement table. If the node is long (will not fit
     * within the statement table), it is be stored in a separate table for that
     * node type.
     * 
     * In addition, for resources (URI, blank nodes), the URI may be optionally
     * compressed. Below, the possibilites are enumerated.
     * 
     * Literal Encoding in Statement Tables Short Literal:
     * Lv:[langLen]:[datatypeLen]:[langString][datatypeString]value[:] Long
     * Literal: Lr:dbid Literal Encoding in Long Literal Table Literal:
     * Lv:[langLen]:[datatypeLen]:[langString][datatypeString]head[:] hash tail
     * 
     * Comments: L indicates a literal v indicates a value r indicates a
     * reference to another table : is used as a delimiter. note that MySQL
     * trims trailing white space for certain VARCHAR columns so an extra
     * delimiter is appended when necessary for those columns. it is not
     * required for dbid, however. dbid references the long literal table
     * langLen is the length of the language identifier for the literal
     * langString is the language identifier datatypeLen is the length of the
     * datatype for the literal datatypeString is the datatype for the literal
     * value is the lexical form of the string head is a prefix of value that
     * can be indexed hash is the CRC32 hash value for the tail tail is the
     * remainder of the value that cannot be indexed
     * 
     * 
     * 
     * URI Encoding in Statement Tables Short URI: Uv:[pfx_dbid]:URI[:] Long
     * URI: Ur:[pfx_dbid]:dbid URI Encoding in Long URI Table URI: Uv:head[:]
     * hash tail
     * 
     * Comments: U indicates a URI pfx_dbid references the prefix table. if the
     * prefix is too short (i.e., the length of the prefix is less than
     * URI_COMPRESS_LENGTH), the URI is not compressed and pfx_dbid is null. URI
     * is the complete URI other notation same as for literal encoding
     * 
     * Blank Node Encoding in Statement Tables Short URI: Bv:[pfx_dbid]:bnid[:]
     * Long URI: Br:[pfx_dbid]:dbid Blank Encoding in Long URI Table URI:
     * Bv:head[:] hash tail
     * 
     * Comments: B indicates a blank node bnid is the blank node identifier
     * other notation same as above Note: currently, blank nodes are always
     * stored uncompressed (pfix_dbid is null).
     * 
     * Variable Node Encoding in Statement Tables Variable Node: Vv:name
     * 
     * Comments: V indicates a variable node v indicates a value name is the
     * variable name Note: the length must be less than LONG_OBJECT_LENGTH
     * 
     * ANY Node Encoding in Statement Tables Variable Node: Av:
     * 
     * Prefix Encoding in Prefix Table Prefix: Pv:val[:] [hash] [tail]
     * 
     * Comments: P indicates a prefix other notation same as above hash and tail
     * are only required for long prefixes.
     *  
     */

    private static String RDB_CODE_URI = "U";

    private static String RDB_CODE_BLANK = "B";

    private static String RDB_CODE_LITERAL = "L";

    private static String RDB_CODE_VARIABLE = "V";

    private static String RDB_CODE_ANY = "A";

    private static String RDB_CODE_VALUE = "v";

    private static String RDB_CODE_DELIM = ":";

    private static char RDB_CODE_DELIM_CHAR = ':';

    private static String nodeToString(Node node) throws RDFRDBException {
        String res;
        if (node.isURI()) {
            String uri = new String(((Node_URI) node).getURI());
            if (uri.startsWith(RDB_CODE_URI)) {
                throw new RDFRDBException("URI Node looks like a blank node: " + 
                                           uri);
            }
            String pfx = RDB_CODE_DELIM + RDB_CODE_DELIM;
            String qname = uri;
            res = RDB_CODE_URI + RDB_CODE_VALUE + pfx + qname;
        } else if (node.isLiteral()) {
            Node_Literal litNode = (Node_Literal) node;
            LiteralLabel ll = litNode.getLiteral();
            String lval = ll.getLexicalForm();
            String lang = ll.language();
            String dtype = ll.getDatatypeURI();
            String ld = litLangTypeToRDBString(lang, dtype);
            res = RDB_CODE_LITERAL + RDB_CODE_VALUE + RDB_CODE_DELIM + ld + lval;
        } else if (node.isBlank()) {
            String bnID = node.getBlankNodeId().toString();
            String delims = "::";
            res = RDB_CODE_BLANK + RDB_CODE_VALUE + delims + bnID;
        } else if (node.isVariable()) {
            String name = ((Node_Variable) node).getName();
            res = RDB_CODE_VARIABLE + RDB_CODE_VALUE + RDB_CODE_DELIM + name;
        } else if (node.equals(Node.ANY)) {
             res = RDB_CODE_ANY + RDB_CODE_VALUE + RDB_CODE_DELIM;
        } else {
            throw new RDFRDBException("Expected Concrete Node, got "
                    + node.toString());
        }
        return res;
    }

    	private static Node stringToNode(String rdbString) throws RDFRDBException {
        Node res = null;
        int len = rdbString.length();
        if (len < 3)
            throw new RDFRDBException("Bad RDBString Header: " + rdbString);
        String nodeType = rdbString.substring(0, 1);
        String valType = rdbString.substring(1, 2);
        if ((!valType.equals(RDB_CODE_VALUE))
                || (rdbString.charAt(2) != RDB_CODE_DELIM_CHAR))
            throw new RDFRDBException("Bad RDBString Header: " + rdbString);
        int pos = 3;
        if (nodeType.equals(RDB_CODE_URI)) {
            ParseInt pi = new ParseInt(pos);
            String prefix = "";
            rdbStringParseInt(rdbString, pi, false);
            pos = pi.pos + 1;
            String qname = rdbString.substring(pos, len);
            res = Node.createURI(prefix + qname);
        } else if (nodeType.equals(RDB_CODE_LITERAL)) {
            //TODO: Parse to correct datatype
            ParseInt pi = new ParseInt(pos);
            String litString = null;
            litString = rdbString.substring(pos, len);
            len = litString.length();
            String lang;
            String dType;
            int langLen = 0;
            int dTypeLen = 0;
            LiteralLabel llabel;
            pi.pos = 0;
            rdbStringParseInt(litString, pi, false);
            if (pi.val == null)
                langLen = 0;
            else
                langLen = pi.val.intValue();
            pi.pos = pi.pos + 1;
            rdbStringParseInt(litString, pi, false);
            if (pi.val == null)
                dTypeLen = 0;
            else
                dTypeLen = pi.val.intValue();
            pos = pi.pos + 1;
            if ((pos + langLen + dTypeLen) > len)
                throw new RDFRDBException("Malformed Literal: " + litString);
            lang = litString.substring(pos, pos + langLen);
            pos = pos + langLen;
            dType = litString.substring(pos, pos + dTypeLen);
            pos = pos + dTypeLen;
            String val = litString.substring(pos);
            if ((dType == null) || (dType.equals(""))) {
                llabel = new LiteralLabel(val, lang == null ? "" : lang);
            } else {
                RDFDatatype dt = TypeMapper.getInstance().getSafeTypeByName(dType);
                llabel = new LiteralLabel(val, lang == null ? "" : lang, dt);
            }
            res = Node.createLiteral(llabel);
        } else if (nodeType.equals(RDB_CODE_BLANK)) {
            String bstr = rdbString.substring(4, len);
            res = Node.createAnon(new AnonId(bstr));
        } else if (nodeType.equals(RDB_CODE_VARIABLE)) {
            String vname = rdbString.substring(3, len);
            res = Node.createVariable(vname);
        } else if (nodeType.equals(RDB_CODE_ANY)) {
            res = Node.ANY;
        } else
            throw new RDFRDBException("Invalid RDBString Prefix, " + rdbString);
        return res;
    }

    private final static class ParseInt {
        int pos;

        Integer val;

        ParseInt(int p) {
            pos = p;
        }
    }

    private static void rdbStringParseInt(String rdbString, ParseInt pi,
            boolean toEnd) {
        int npos = toEnd ? rdbString.length() : rdbString.indexOf(
                RDB_CODE_DELIM_CHAR, pi.pos);
        if (npos < 0) {
            throw new RDFRDBException("Bad RDB String: " + rdbString);
        }
        String intStr = rdbString.substring(pi.pos, npos);
        pi.pos = npos;
        if (intStr.equals(""))
            pi.val = null;
        else
            try {
                pi.val = new Integer(intStr);
            } catch (NumberFormatException e1) {
                throw new RDFRDBException("Bad RDB String: " + rdbString);
            }
        return;
    }

    /**
     * Encode a literal node's lang and datatype as a string of the form
     * ":[langLen]:[datatypeLen]:[langString][dataTypeString]"
     * 
     * @return the string.
     */
    private static String litLangTypeToRDBString(String lang, String dtype)
            throws RDFRDBException {
        String res = RDB_CODE_DELIM;
        res = ((lang == null) ? "" : Integer.toString(lang.length()))
                + RDB_CODE_DELIM;
        res = res + ((dtype == null) ? "" : Integer.toString(dtype.length()))
                + RDB_CODE_DELIM;
        res = res + (lang == null ? "" : lang) + (dtype == null ? "" : dtype);
        return res;
    }

    public static void writeTriple(Triple triple, ObjectOutput out) throws RDFRDBException, IOException {
        out.writeUTF(nodeToString(triple.getSubject()));
        out.writeUTF(nodeToString(triple.getPredicate()));
        out.writeUTF(nodeToString(triple.getObject()));
    }

    public static Triple readTriple(ObjectInput in) throws RDFRDBException, IOException {
        Node subject = TripleUtil.stringToNode(in.readUTF());
        Node predicate = TripleUtil.stringToNode(in.readUTF());
        Node object = TripleUtil.stringToNode(in.readUTF());
        return new Triple(subject, predicate, object);
    }

}

/*
 * (c) Copyright 2000, 2001 Hewlett-Packard Development Company, LP All rights
 * reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer. 2. 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. 3. The name of the author may not
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 THE AUTHOR 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, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

Index: DeleteTripleCommand.java
===================================================================
RCS file: /cvsroot/javaowl/JavaOWL/src/org/javaowl/models/prevalence/DeleteTripleCommand.java,v
retrieving revision 1.2
retrieving revision 1.3
diff -C2 -d -r1.2 -r1.3
*** DeleteTripleCommand.java	27 Jul 2004 16:20:00 -0000	1.2
--- DeleteTripleCommand.java	28 Jul 2004 06:54:07 -0000	1.3
***************
*** 20,38 ****
  package org.javaowl.models.prevalence;
  
! import com.hp.hpl.jena.graph.Node;
! import com.hp.hpl.jena.graph.Triple;
  
  import org.prevayler.Command;
  import org.prevayler.PrevalentSystem;
  
! import java.io.IOException;
! import java.io.ObjectInputStream;
! import java.io.ObjectOutputStream;
! import java.io.Serializable;
! 
! class DeleteTripleCommand implements Command {
  
!     private transient Triple triple;
  
      DeleteTripleCommand(Triple triple) {
          this.triple = triple;
--- 20,42 ----
  package org.javaowl.models.prevalence;
  
! import java.io.Externalizable;
! import java.io.IOException;
! import java.io.ObjectInput;
! import java.io.ObjectOutput;
! import java.io.Serializable;
  
  import org.prevayler.Command;
  import org.prevayler.PrevalentSystem;
  
! import com.hp.hpl.jena.graph.Triple;
  
! class DeleteTripleCommand implements Command, Externalizable {
  
+     private static final long serialVersionUID = -4089954040389955762L;
+     
+     private Triple triple;
+     
+     public DeleteTripleCommand() {}
+     
      DeleteTripleCommand(Triple triple) {
          this.triple = triple;
***************
*** 44,59 ****
      }
  
!     private void writeObject(ObjectOutputStream out) throws IOException {
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getSubject()));
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getPredicate()));
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getObject()));
      }
  
!     private void readObject(ObjectInputStream in) throws IOException,
!             ClassNotFoundException {
!         Node subject = StorageUtil.rdbStringToNode(in.readUTF());
!         Node predicate = StorageUtil.rdbStringToNode(in.readUTF());
!         Node object = StorageUtil.rdbStringToNode(in.readUTF());
!         this.triple = new Triple(subject, predicate, object);
      }
  }
--- 48,57 ----
      }
  
!     public void writeExternal(ObjectOutput out) throws IOException {
!         TripleUtil.writeTriple(triple, out); 
      }
  
!     public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
!         this.triple = TripleUtil.readTriple(in);
      }
  }

--- StorageUtil.java DELETED ---

Index: StorageGraph.java
===================================================================
RCS file: /cvsroot/javaowl/JavaOWL/src/org/javaowl/models/prevalence/StorageGraph.java,v
retrieving revision 1.2
retrieving revision 1.3
diff -C2 -d -r1.2 -r1.3
*** StorageGraph.java	26 Jul 2004 22:55:02 -0000	1.2
--- StorageGraph.java	28 Jul 2004 06:54:07 -0000	1.3
***************
*** 20,24 ****
--- 20,31 ----
  package org.javaowl.models.prevalence;
  
+ import java.io.Externalizable;
+ import java.io.IOException;
+ import java.io.ObjectInput;
+ import java.io.ObjectOutput;
+ import java.util.Iterator;
+ 
  import com.hp.hpl.jena.graph.Graph;
+ import com.hp.hpl.jena.graph.GraphUtil;
  import com.hp.hpl.jena.graph.Triple;
  import com.hp.hpl.jena.graph.Node;
***************
*** 37,46 ****
  import com.hp.hpl.jena.util.iterator.ExtendedIterator;
  
  import org.prevayler.implementation.AbstractPrevalentSystem;
  
! class StorageGraph extends AbstractPrevalentSystem implements Graph {
  
      private final Graph graph = new GraphMem(ReificationStyle.Standard);
         
      public boolean dependsOn(Graph other) { 
          return graph.dependsOn(other); 
--- 44,58 ----
  import com.hp.hpl.jena.util.iterator.ExtendedIterator;
  
+ import org.prevayler.AlarmClock;
  import org.prevayler.implementation.AbstractPrevalentSystem;
  
! class StorageGraph extends AbstractPrevalentSystem implements Graph, Externalizable {
  
+     private static final long serialVersionUID = 792795079693766654L;
+     
      private final Graph graph = new GraphMem(ReificationStyle.Standard);
         
+     public StorageGraph() {}
+     
      public boolean dependsOn(Graph other) { 
          return graph.dependsOn(other); 
***************
*** 53,57 ****
      }
      public BulkUpdateHandler getBulkUpdateHandler() { 
!         return graph.getBulkUpdateHandler();
      }
      public Capabilities getCapabilities() { 
--- 65,69 ----
      }
      public BulkUpdateHandler getBulkUpdateHandler() { 
!         throw new UnsupportedOperationException();
      }
      public Capabilities getCapabilities() { 
***************
*** 97,99 ****
--- 109,126 ----
          graph.add(t);
      }
+     
+     public void writeExternal(ObjectOutput out) throws IOException {
+        out.writeInt(size());
+        out.writeObject(clock());
+        for (Iterator it = GraphUtil.findAll(graph); it.hasNext(); ) {
+            TripleUtil.writeTriple((Triple) it.next(), out);
+        }
+     }
+     public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
+         int size = in.readInt();
+         clock((AlarmClock) in.readObject());
+         for(int i = 0; i < size; i++) {
+             add(TripleUtil.readTriple(in));
+         	}
+     }
  }

Index: PrevalentGraph.java
===================================================================
RCS file: /cvsroot/javaowl/JavaOWL/src/org/javaowl/models/prevalence/PrevalentGraph.java,v
retrieving revision 1.2
retrieving revision 1.3
diff -C2 -d -r1.2 -r1.3
*** PrevalentGraph.java	26 Jul 2004 22:55:02 -0000	1.2
--- PrevalentGraph.java	28 Jul 2004 06:54:07 -0000	1.3
***************
*** 21,28 ****
--- 21,31 ----
  
  import java.io.IOException;
+ import java.util.Iterator;
+ import java.util.List;
  
  import org.prevayler.implementation.SnapshotPrevayler;
  
  import com.hp.hpl.jena.graph.Graph;
+ import com.hp.hpl.jena.graph.GraphUtil;
  import com.hp.hpl.jena.graph.Triple;
  import com.hp.hpl.jena.graph.Node;
***************
*** 39,43 ****
  import com.hp.hpl.jena.util.iterator.ExtendedIterator;
  
! public class PrevalentGraph implements Graph, Runnable{
  
      private final SnapshotPrevayler prevayler;
--- 42,46 ----
  import com.hp.hpl.jena.util.iterator.ExtendedIterator;
  
! public class PrevalentGraph implements Graph, BulkUpdateHandler, Runnable{
  
      private final SnapshotPrevayler prevayler;
***************
*** 47,50 ****
--- 50,54 ----
          prevayler = new SnapshotPrevayler(new StorageGraph(), directory);
          storageGraph = (StorageGraph) prevayler.system();
+         new Thread(this).start();
      }
      
***************
*** 52,55 ****
--- 56,62 ----
          for (;;) {
              try {
+                 prevayler.takeSnapshot();
+                 System.err.println("Snapshot taken at " + new java.util.Date() + "...");
+ 
                  try {
                      Thread.sleep(1000 * 60 * 60 * 24); 
***************
*** 57,62 ****
                      //Ignore
                  }
-                 prevayler.takeSnapshot();
-                 System.err.println("Snapshot taken at " + new java.util.Date() + "...");
              } catch (IOException e) {
                  e.printStackTrace();
--- 64,67 ----
***************
*** 78,82 ****
  
      public BulkUpdateHandler getBulkUpdateHandler() { 
!         return storageGraph.getBulkUpdateHandler();
      }
  
--- 83,87 ----
  
      public BulkUpdateHandler getBulkUpdateHandler() { 
!         return this;
      }
  
***************
*** 146,148 ****
--- 151,201 ----
          }
      }
+ 
+     public void add(Triple[] triples) {
+         for (int i = 0; i < triples.length; i++) {
+             add(triples[i]);
+         	}
+     }
+ 
+     public void add(List triples) {
+         add(triples.iterator());
+     }
+ 
+     public void add(Iterator it) {
+         while (it.hasNext()) {
+             add((Triple) it.next());
+         }
+     }
+ 
+     public void add(Graph graph, boolean withReifications) {
+         add(GraphUtil.findAll(graph));
+     }
+ 
+     public void add(Graph graph) {
+ 	    add(graph, false);
+     }
+ 
+     public void delete(Triple[] triples) {
+         for (int i = 0; i < triples.length; i++) {
+             delete(triples[i]);
+         	}
+     }
+ 
+     public void delete(List triples) {
+         delete(triples.iterator());
+     }
+ 
+     public void delete(Iterator it) {
+         while (it.hasNext()) {
+             delete((Triple) it.next());
+         }  
+     }
+ 
+     public void delete(Graph graph) {
+         delete(graph, false);
+     }
+ 
+     public void delete(Graph graph, boolean withReifications) {
+         delete(GraphUtil.findAll(graph));
+     }
  }

Index: AddTripleCommand.java
===================================================================
RCS file: /cvsroot/javaowl/JavaOWL/src/org/javaowl/models/prevalence/AddTripleCommand.java,v
retrieving revision 1.6
retrieving revision 1.7
diff -C2 -d -r1.6 -r1.7
*** AddTripleCommand.java	27 Jul 2004 16:20:00 -0000	1.6
--- AddTripleCommand.java	28 Jul 2004 06:54:07 -0000	1.7
***************
*** 20,38 ****
  package org.javaowl.models.prevalence;
  
! import com.hp.hpl.jena.graph.Node;
! import com.hp.hpl.jena.graph.Triple;
  
  import org.prevayler.Command;
  import org.prevayler.PrevalentSystem;
  
! import java.io.Serializable;
! import java.io.ObjectInputStream;
! import java.io.ObjectOutputStream;
! import java.io.IOException;
! 
! class AddTripleCommand implements Command {
  
!     private transient Triple triple;
  
      AddTripleCommand(Triple triple) {
          this.triple = triple;
--- 20,42 ----
  package org.javaowl.models.prevalence;
  
! import java.io.Externalizable;
! import java.io.IOException;
! import java.io.ObjectInput;
! import java.io.ObjectOutput;
! import java.io.Serializable;
  
  import org.prevayler.Command;
  import org.prevayler.PrevalentSystem;
  
! import com.hp.hpl.jena.graph.Triple;
  
! class AddTripleCommand implements Command, Externalizable {
  
+     private static final long serialVersionUID = -8900004762584176922L;
+     
+     private Triple triple;
+     
+     public AddTripleCommand() {}
+     
      AddTripleCommand(Triple triple) {
          this.triple = triple;
***************
*** 44,59 ****
      }
  
!     private void writeObject(ObjectOutputStream out) throws IOException {
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getSubject()));
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getPredicate()));
!         out.writeUTF(StorageUtil.nodeToRDBString(triple.getObject()));
      }
  
!     private void readObject(ObjectInputStream in) throws IOException,
!             ClassNotFoundException {
!         Node subject = StorageUtil.rdbStringToNode(in.readUTF());
!         Node predicate = StorageUtil.rdbStringToNode(in.readUTF());
!         Node object = StorageUtil.rdbStringToNode(in.readUTF());
!         this.triple = new Triple(subject, predicate, object);
      }
  }
--- 48,61 ----
      }
  
!     public void writeExternal(ObjectOutput out) throws IOException {
!         TripleUtil.writeTriple(triple, out); 
      }
  
!     public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
!         try {
!             this.triple = TripleUtil.readTriple(in);
!         } catch (Exception e) {
!             e.printStackTrace();    
!     	    }
      }
  }