Index: trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstance.java
===================================================================
--- trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstance.java	(revision 1404)
+++ trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstance.java	(revision 1405)
@@ -69,3 +69,12 @@
     public ITaskInstance clone();
 
+    /**
+     * <p>
+     * implements the visitor pattern to be able to process task instances and their children.
+     * </p>
+     * 
+     * @param visitor the visitor used to process the task
+     */
+    public void accept(ITaskInstanceVisitor visitor);
+    
 }
Index: trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstanceVisitor.java
===================================================================
--- trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstanceVisitor.java	(revision 1405)
+++ trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeifc/ITaskInstanceVisitor.java	(revision 1405)
@@ -0,0 +1,83 @@
+//   Copyright 2012 Georg-August-Universität Göttingen, Germany
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+
+package de.ugoe.cs.autoquest.tasktrees.treeifc;
+
+
+/**
+ * <p>
+ * This is an implementation of the visitor pattern. Through this, it is possible to effectively
+ * process a task instance tree. 
+ * </p>
+ * 
+ * @author Patrick Harms
+ */
+public interface ITaskInstanceVisitor {
+
+    /**
+     * <p>
+     * method called for each visited event task instance.
+     * </p>
+     * 
+     * @param eventTaskInstance the event task instance to be processed
+     */
+    public void visit(IEventTaskInstance eventTaskInstance);
+    
+    /**
+     * <p>
+     * method called for each visited iteration instance.
+     * </p>
+     * 
+     * @param iterationInstance the iteration instance to be processed
+     */
+    public void visit(IIterationInstance iterationInstance);
+    
+    /**
+     * <p>
+     * method called for each visited optional instance.
+     * </p>
+     * 
+     * @param optionalInstance the optional instance to be processed
+     */
+    public void visit(IOptionalInstance optionalInstance);
+    
+    /**
+     * <p>
+     * method called for each visited selection instance.
+     * </p>
+     * 
+     * @param selectionInstance the selection instance to be processed
+     */
+    public void visit(ISelectionInstance selectionInstance);
+    
+    /**
+     * <p>
+     * method called for each visited sequence instance.
+     * </p>
+     * 
+     * @param sequenceInstance the sequence instance to be processed
+     */
+    public void visit(ISequenceInstance sequenceInstance);
+
+    /**
+     * <p>
+     * method called for each other kind of visited task instance (implemented to support future
+     * versions).
+     * </p>
+     * 
+     * @param taskInstance the task instance to be processed
+     */
+    public void visit(ITaskInstance taskInstance);
+    
+}
Index: trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskInstance.java
===================================================================
--- trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskInstance.java	(revision 1404)
+++ trunk/autoquest-core-tasktrees/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskInstance.java	(revision 1405)
@@ -17,4 +17,5 @@
 import de.ugoe.cs.autoquest.tasktrees.treeifc.ITask;
 import de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskInstance;
+import de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskInstanceVisitor;
 
 /**
@@ -154,4 +155,12 @@
     }
 
+    /* (non-Javadoc)
+     * @see de.ugoe.cs.autoquest.tasktrees.treeifc.ITaskInstance#accept(ITaskInstanceVisitor)
+     */
+    @Override
+    public void accept(ITaskInstanceVisitor visitor) {
+        visitor.visit(this);
+    }
+
     /**
      * <p>