diff --git a/navalplanner-gantt-zk/pom.xml b/navalplanner-gantt-zk/pom.xml
index dd6820a9a..e2a167f08 100644
--- a/navalplanner-gantt-zk/pom.xml
+++ b/navalplanner-gantt-zk/pom.xml
@@ -31,6 +31,11 @@
             <groupId>commons-logging</groupId>
             <artifactId>commons-logging</artifactId>
         </dependency>
+        <dependency>
+        	<groupId>jgrapht</groupId>
+        	<artifactId>jgrapht</artifactId>
+        	<version>0.7.3</version>
+        </dependency>
     </dependencies>
     
 </project>
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Dependency.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Dependency.java
index 881123873..5a867f6e7 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Dependency.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Dependency.java
@@ -8,6 +8,8 @@ package org.zkoss.ganttz;
 import java.beans.PropertyChangeEvent;
 import java.beans.PropertyChangeListener;
 
+import org.zkoss.ganttz.util.DependencyBean;
+import org.zkoss.ganttz.util.DependencyType;
 import org.zkoss.zk.au.out.AuInvoke;
 import org.zkoss.zk.ui.ext.AfterCompose;
 import org.zkoss.zul.impl.XulElement;
@@ -21,14 +23,6 @@ public class Dependency extends XulElement implements AfterCompose {
 
     private Task source;
 
-    public Task getSource() {
-        return source;
-    }
-
-    public Task getDestination() {
-        return destination;
-    }
-
     private Task destination;
 
     public Dependency() {
@@ -96,4 +90,18 @@ public class Dependency extends XulElement implements AfterCompose {
     public boolean contains(Task task) {
         return getSource().equals(task) || getDestination().equals(task);
     }
+
+    public Task getSource() {
+        return source;
+    }
+
+    public Task getDestination() {
+        return destination;
+    }
+
+    public DependencyBean getDependencyBean() {
+        return new DependencyBean(source.getTaskBean(), destination
+                .getTaskBean(), DependencyType.END_START);
+    }
+
 }
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/DependencyList.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/DependencyList.java
index 6e76c366f..34aa0aa44 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/DependencyList.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/DependencyList.java
@@ -42,6 +42,7 @@ public class DependencyList extends XulElement implements AfterCompose {
     void addDependency(Dependency dependency) {
         appendChild(dependency);
         addContextMenu(dependency);
+        publishDependency(dependency);
     }
 
     private void addContextMenu(Dependency dependency) {
@@ -83,9 +84,24 @@ public class DependencyList extends XulElement implements AfterCompose {
                     taskRemovedListener);
         }
         addContextMenu();
+        publishDependencies();
 
     }
 
+    private void publishDependencies() {
+        for (Dependency dependency : getDependencies()) {
+            publishDependency(dependency);
+        }
+    }
+
+    private void publishDependency(Dependency dependency) {
+        getPlanner().publishDependency(dependency);
+    }
+
+    private Planner getPlanner() {
+        return getGanttPanel().getPlanner();
+    }
+
     private void addContextMenu() {
         for (Dependency dependency : getDependencies()) {
             addContextMenu(dependency);
@@ -94,8 +110,6 @@ public class DependencyList extends XulElement implements AfterCompose {
 
     private Menupopup contextMenu;
 
-    private Dependency dependencyForContextMenu = null;
-
     private Menupopup getContextMenu() {
         if (contextMenu == null) {
             contextMenu = MenuBuilder.on(getPage(), getDependencies()).item(
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/ListDetails.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/ListDetails.java
index 3e1d05d44..41048f601 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/ListDetails.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/ListDetails.java
@@ -33,7 +33,7 @@ public class ListDetails extends HtmlMacroComponent {
         taskDetail.setParent(insertionPoint);
         taskDetail.afterCompose();
         Task task = new Task();
-        getPlanner().addTask(task);
+        getPlanner().publishTask(task);
         task.setColor("yellow");
         task.setId(newId);
     }
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Planner.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Planner.java
index 4eaa4dc68..89807f93c 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Planner.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Planner.java
@@ -5,6 +5,8 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.zkoss.ganttz.util.DependencyRegistry;
+import org.zkoss.ganttz.util.TaskBean;
 import org.zkoss.zk.ui.ext.AfterCompose;
 import org.zkoss.zul.impl.XulElement;
 
@@ -14,6 +16,8 @@ public class Planner extends XulElement implements AfterCompose {
 
     private Map<String, TaskBean> tasksById = new HashMap<String, TaskBean>();
 
+    private DependencyRegistry dependencyRegistry = new DependencyRegistry();
+
     public Planner() {
     }
 
@@ -42,6 +46,7 @@ public class Planner extends XulElement implements AfterCompose {
             throw new IllegalArgumentException("task with id " + taskId
                     + " is already in " + tasksById);
         tasksById.put(taskId, task);
+        dependencyRegistry.add(task);
     }
 
     TaskBean retrieve(String taskId) {
@@ -78,10 +83,21 @@ public class Planner extends XulElement implements AfterCompose {
             }
         };
         taskList.addDependencyListener(dependencyAddedListener);
+        taskList.addTaskRemovedListener(new TaskRemovedListener() {
+            @Override
+            public void taskRemoved(Task taskRemoved) {
+                dependencyRegistry.remove(taskRemoved.getTaskBean());
+            }
+        });
     }
 
-    public void addTask(Task task) {
+    public void publishTask(Task task) {
         getTaskList().addTask(task);
+        dependencyRegistry.add(task.getTaskBean());
+    }
+
+    public void publishDependency(Dependency dependency) {
+        dependencyRegistry.add(dependency);
     }
 
 }
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Task.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Task.java
index 87f0c4525..04643e73d 100755
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Task.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/Task.java
@@ -15,6 +15,7 @@ import java.util.ListIterator;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.zkoss.ganttz.util.TaskBean;
 import org.zkoss.lang.Objects;
 import org.zkoss.xml.HTMLs;
 import org.zkoss.zk.au.AuRequest;
@@ -212,9 +213,9 @@ public class Task extends Div {
         this.taskBean.setLengthMilliseconds(getMapper().toMilliseconds(pixels));
     }
 
-    void doAddDependency(String dependencyId) {
+    void doAddDependency(String destinyTaskId) {
         Dependency dependency = new Dependency(this,
-                ((Task) getFellow(dependencyId)));
+                ((Task) getFellow(destinyTaskId)));
         fireDependenceAdded(dependency);
     }
 
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
index 413801f14..6913ebe60 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
@@ -14,6 +14,7 @@ import java.util.regex.Pattern;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.zkoss.ganttz.util.TaskBean;
 import org.zkoss.zk.ui.AbstractComponent;
 import org.zkoss.zk.ui.HtmlMacroComponent;
 import org.zkoss.zk.ui.ext.AfterCompose;
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskEditFormComposer.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskEditFormComposer.java
index 2c6c93f21..84df5ec13 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskEditFormComposer.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskEditFormComposer.java
@@ -3,6 +3,7 @@ package org.zkoss.ganttz;
 import java.beans.PropertyChangeEvent;
 import java.beans.PropertyChangeListener;
 
+import org.zkoss.ganttz.util.TaskBean;
 import org.zkoss.zk.ui.Component;
 import org.zkoss.zk.ui.event.Event;
 import org.zkoss.zk.ui.util.GenericForwardComposer;
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyBean.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyBean.java
new file mode 100644
index 000000000..7b80951a5
--- /dev/null
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyBean.java
@@ -0,0 +1,113 @@
+package org.zkoss.ganttz.util;
+
+import java.util.Collection;
+import java.util.Date;
+
+/**
+ * This class represents a dependency. Contains the source and the destination.
+ * It also specifies the type of the relationship. <br/>
+ * Created at Apr 24, 2009
+ * 
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ * 
+ */
+public class DependencyBean {
+
+    private enum Calculation {
+        START, END;
+    }
+
+    public static Date calculateStart(TaskBean origin, Date current,
+            Collection<? extends DependencyBean> dependencies) {
+        return apply(Calculation.START, origin, current, dependencies);
+    }
+
+    public static Date calculateEnd(TaskBean origin, Date current,
+            Collection<? extends DependencyBean> depencencies) {
+        return apply(Calculation.END, origin, current, depencencies);
+    }
+
+    private static Date apply(Calculation calculation, TaskBean origin,
+            Date current, Collection<? extends DependencyBean> dependencies) {
+        for (DependencyBean dependency : dependencies) {
+            switch (calculation) {
+            case START:
+                current = dependency.getType().calculateStartDestinyTask(
+                        dependency.getSource(), current);
+                break;
+            case END:
+                current = dependency.getType().calculateEndDestinyTask(
+                        dependency.getSource(), current);
+                break;
+            default:
+                throw new RuntimeException("unexpected calculation "
+                        + calculation);
+            }
+        }
+        return current;
+    }
+
+    private final TaskBean source;
+
+    private final TaskBean destination;
+
+    private final DependencyType type;
+
+    public DependencyBean(TaskBean source, TaskBean destination,
+            DependencyType type) {
+        if (source == null)
+            throw new IllegalArgumentException("source cannot be null");
+        if (destination == null)
+            throw new IllegalArgumentException("destination cannot be null");
+        if (type == null)
+            throw new IllegalArgumentException("type cannot be null");
+        this.source = source;
+        this.destination = destination;
+        this.type = type;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result
+                + ((destination == null) ? 0 : destination.hashCode());
+        result = prime * result + ((source == null) ? 0 : source.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        DependencyBean other = (DependencyBean) obj;
+        if (destination == null) {
+            if (other.destination != null)
+                return false;
+        } else if (!destination.equals(other.destination))
+            return false;
+        if (source == null) {
+            if (other.source != null)
+                return false;
+        } else if (!source.equals(other.source))
+            return false;
+        return true;
+    }
+
+    public TaskBean getSource() {
+        return source;
+    }
+
+    public TaskBean getDestination() {
+        return destination;
+    }
+
+    public DependencyType getType() {
+        return type;
+    }
+
+}
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyRegistry.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyRegistry.java
new file mode 100644
index 000000000..7aadad658
--- /dev/null
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyRegistry.java
@@ -0,0 +1,107 @@
+package org.zkoss.ganttz.util;
+
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.jgrapht.DirectedGraph;
+import org.jgrapht.graph.SimpleDirectedGraph;
+import org.zkoss.ganttz.Dependency;
+
+/**
+ * This class contains a graph with the {@link TaskBean tasks} as vertexes and
+ * the {@link DependencyBean dependency} as arcs. It enforces the rules embodied
+ * in the dependencies and in the duration of the tasks using listeners. <br/>
+ * Created at Apr 24, 2009
+ * 
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ * 
+ */
+public class DependencyRegistry {
+
+    private final DirectedGraph<TaskBean, DependencyBean> graph = new SimpleDirectedGraph<TaskBean, DependencyBean>(
+            DependencyBean.class);
+
+    private Map<TaskBean, RulesEnforcer> rulesEnforcersByTask = new HashMap<TaskBean, RulesEnforcer>();
+
+    private List<RulesEnforcer> getOutgoing(TaskBean task) {
+        ArrayList<RulesEnforcer> result = new ArrayList<RulesEnforcer>();
+        for (DependencyBean dependencyBean : graph.outgoingEdgesOf(task)) {
+            result.add(rulesEnforcersByTask
+                    .get(dependencyBean.getDestination()));
+        }
+        return result;
+    }
+
+    private class RulesEnforcer {
+        private final TaskBean task;
+
+        private RulesEnforcer(TaskBean task) {
+            if (task == null)
+                throw new IllegalArgumentException("task cannot be null");
+            this.task = task;
+            this.task.addPropertyChangeListener(new PropertyChangeListener() {
+
+                @Override
+                public void propertyChange(PropertyChangeEvent evt) {
+                    RulesEnforcer.this.update();
+                    updateOutgoing(RulesEnforcer.this.task);
+                }
+            });
+        }
+
+        void update() {
+            Set<DependencyBean> incoming = graph.incomingEdgesOf(task);
+            Date beginDate = task.getBeginDate();
+            Date newStart = DependencyBean.calculateStart(task, beginDate,
+                    incoming);
+            if (!beginDate.equals(newStart))
+                task.setBeginDate(newStart);
+            Date endDate = task.getEndDate();
+            Date newEnd = DependencyBean.calculateEnd(task, endDate, incoming);
+            if (!endDate.equals(newEnd)) {
+                task.setEndDate(newEnd);
+            }
+        }
+    }
+
+    public void add(TaskBean task) {
+        graph.addVertex(task);
+        rulesEnforcersByTask.put(task, new RulesEnforcer(task));
+    }
+
+    public void remove(TaskBean task) {
+        graph.removeVertex(task);
+        rulesEnforcersByTask.remove(task);
+        updateOutgoing(task);
+    }
+
+    private void updateOutgoing(TaskBean task) {
+        for (RulesEnforcer rulesEnforcer : getOutgoing(task)) {
+            rulesEnforcer.update();
+        }
+    }
+
+    public void remove(Dependency dependency) {
+        graph.removeEdge(dependency.getDependencyBean());
+        TaskBean destination = dependency.getDependencyBean().getDestination();
+        rulesEnforcersByTask.get(destination).update();
+    }
+
+    public void add(Dependency dependency) {
+        TaskBean destination = dependency.getDestination().getTaskBean();
+        graph.addEdge(dependency.getSource().getTaskBean(), destination,
+                dependency.getDependencyBean());
+        getEnforcer(destination).update();
+    }
+
+    private RulesEnforcer getEnforcer(TaskBean destination) {
+        return rulesEnforcersByTask.get(destination);
+    }
+
+}
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyType.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyType.java
new file mode 100644
index 000000000..15b4644af
--- /dev/null
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/DependencyType.java
@@ -0,0 +1,51 @@
+package org.zkoss.ganttz.util;
+
+import java.util.Date;
+
+/**
+ * This enum tells the type of a depepdency. Each instance contanins the correct
+ * behaviour for that type of dependency . <br/>
+ * Created at Apr 24, 2009
+ * 
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ * 
+ */
+public enum DependencyType {
+
+    VOID {
+        @Override
+        public Date calculateEndDestinyTask(TaskBean originalTask, Date current) {
+            return current;
+        }
+
+        @Override
+        public Date calculateStartDestinyTask(TaskBean originalTask,
+                Date current) {
+            return current;
+        }
+    },
+    END_START {
+        @Override
+        public Date calculateEndDestinyTask(TaskBean originalTask, Date current) {
+            return current;
+        }
+
+        @Override
+        public Date calculateStartDestinyTask(TaskBean originalTask,
+                Date current) {
+            return getBigger(originalTask.getEndDate(), current);
+        }
+    };
+
+    private static Date getBigger(Date date1, Date date2) {
+        if (date1.before(date2))
+            return date2;
+        return date1;
+    }
+
+    public abstract Date calculateEndDestinyTask(TaskBean originTask,
+            Date current);
+
+    public abstract Date calculateStartDestinyTask(TaskBean originTask,
+            Date current);
+}
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskBean.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
similarity index 91%
rename from navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskBean.java
rename to navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
index 6b42056ce..08fc065c1 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskBean.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
@@ -1,9 +1,17 @@
-package org.zkoss.ganttz;
+package org.zkoss.ganttz.util;
 
 import java.beans.PropertyChangeListener;
 import java.beans.PropertyChangeSupport;
 import java.util.Date;
 
+/**
+ * This class contains the information of a task. It can be modified and
+ * notifies of the changes to the interested parties. <br/>
+ * Created at Apr 24, 2009
+ * 
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ * 
+ */
 public class TaskBean {
 
     private PropertyChangeSupport propertyChangeSupport = new PropertyChangeSupport(