Preliminary checkin for implementing version aware topology state.
diff --git a/core/store/src/main/java/org/onlab/onos/store/impl/OnosTimestamp.java b/core/store/src/main/java/org/onlab/onos/store/impl/OnosTimestamp.java
index f994e02..5b68d1a 100644
--- a/core/store/src/main/java/org/onlab/onos/store/impl/OnosTimestamp.java
+++ b/core/store/src/main/java/org/onlab/onos/store/impl/OnosTimestamp.java
@@ -1,11 +1,9 @@
 package org.onlab.onos.store.impl;
 
-import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkArgument;
 
 import java.util.Objects;
 
-import org.onlab.onos.net.ElementId;
 import org.onlab.onos.store.Timestamp;
 
 import com.google.common.base.MoreObjects;
@@ -14,22 +12,20 @@
 // If it is store specific, implement serializable interfaces?
 /**
  * Default implementation of Timestamp.
+ * TODO: Better documentation.
  */
 public final class OnosTimestamp implements Timestamp {
 
-    private final ElementId id;
     private final int termNumber;
     private final int sequenceNumber;
 
     /**
      * Default version tuple.
      *
-     * @param id identifier of the element
      * @param termNumber the mastership termNumber
      * @param sequenceNumber  the sequenceNumber number within the termNumber
      */
-    public OnosTimestamp(ElementId id, int termNumber, int sequenceNumber) {
-        this.id = checkNotNull(id);
+    public OnosTimestamp(int termNumber, int sequenceNumber) {
         this.termNumber = termNumber;
         this.sequenceNumber = sequenceNumber;
     }
@@ -38,9 +34,6 @@
     public int compareTo(Timestamp o) {
         checkArgument(o instanceof OnosTimestamp, "Must be OnosTimestamp", o);
         OnosTimestamp that = (OnosTimestamp) o;
-        checkArgument(this.id.equals(that.id),
-                "Cannot compare version for different element this:%s, that:%s",
-                    this, that);
 
         return ComparisonChain.start()
                 .compare(this.termNumber, that.termNumber)
@@ -50,7 +43,7 @@
 
     @Override
     public int hashCode() {
-        return Objects.hash(id, termNumber, sequenceNumber);
+        return Objects.hash(termNumber, sequenceNumber);
     }
 
     @Override
@@ -62,30 +55,19 @@
             return false;
         }
         OnosTimestamp that = (OnosTimestamp) obj;
-        return Objects.equals(this.id, that.id) &&
-                Objects.equals(this.termNumber, that.termNumber) &&
+        return Objects.equals(this.termNumber, that.termNumber) &&
                 Objects.equals(this.sequenceNumber, that.sequenceNumber);
     }
 
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
-                    .add("id", id)
                     .add("termNumber", termNumber)
                     .add("sequenceNumber", sequenceNumber)
                     .toString();
     }
 
     /**
-     * Returns the element.
-     *
-     * @return element identifier
-     */
-    public ElementId id() {
-        return id;
-    }
-
-    /**
      * Returns the termNumber.
      *
      * @return termNumber
@@ -102,4 +84,4 @@
     public int sequenceNumber() {
         return sequenceNumber;
     }
-}
+}
\ No newline at end of file