diff --git a/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/Constraint.java b/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/Constraint.java
index 719e8c7ce..1e72d939e 100644
--- a/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/Constraint.java
+++ b/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/Constraint.java
@@ -53,6 +53,24 @@ public abstract class Constraint<T> {
         return result;
     }
 
+    private static final Constraint<Object> VOID_CONSTRAINT = new Constraint<Object>() {
+
+        @Override
+        protected Object applyConstraintTo(Object currentValue) {
+            return currentValue;
+        }
+
+        @Override
+        public boolean isSatisfiedBy(Object value) {
+            return true;
+        }
+    };
+
+    @SuppressWarnings("unchecked")
+    public static <T> Constraint<T> voidConstraint() {
+        return (Constraint<T>) VOID_CONSTRAINT;
+    }
+
     private WeakReferencedListeners<IConstraintViolationListener<T>> weakListeners = WeakReferencedListeners
             .create();
 
diff --git a/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/DateConstraint.java b/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/DateConstraint.java
new file mode 100644
index 000000000..97cbeec50
--- /dev/null
+++ b/ganttzk/src/main/java/org/zkoss/ganttz/data/constraint/DateConstraint.java
@@ -0,0 +1,87 @@
+/*
+ * This file is part of ###PROJECT_NAME###
+ *
+ * Copyright (C) 2009 Fundación para o Fomento da Calidade Industrial e
+ *                    Desenvolvemento Tecnolóxico de Galicia
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.zkoss.ganttz.data.constraint;
+
+import java.util.Date;
+
+/**
+ * A constraint applied to {@link Date dates} <br />
+ * @author Óscar González Fernández <ogonzalez@igalia.com>
+ */
+public abstract class DateConstraint extends Constraint<Date> {
+
+    public static Constraint<Date> biggerOrEqualThan(Date date) {
+        if (date == null) {
+            return Constraint.voidConstraint();
+        }
+        return new BiggerOrEqualThan(date);
+    }
+
+    private long value;
+
+    protected long getValue() {
+        return value;
+    }
+
+    protected DateConstraint(Date date) {
+        this.value = asMilliseconds(date);
+    }
+
+    @Override
+    protected Date applyConstraintTo(Date currentValue) {
+        return new Date(applyConstraintTo(asMilliseconds(currentValue)));
+    }
+
+    private Long asMilliseconds(Date date) {
+        return date != null ? date.getTime() : null;
+    }
+
+    protected abstract long applyConstraintTo(Long time);
+
+    @Override
+    public boolean isSatisfiedBy(Date value) {
+        return isSatisfiedBy(asMilliseconds(value));
+    }
+
+    protected abstract boolean isSatisfiedBy(Long time);
+
+    static class BiggerOrEqualThan extends DateConstraint {
+
+        protected BiggerOrEqualThan(Date date) {
+            super(date);
+        }
+
+        @Override
+        protected long applyConstraintTo(Long time) {
+            if (time == null) {
+                return getValue();
+            }
+            return Math.max(getValue(), time);
+        }
+
+        @Override
+        protected boolean isSatisfiedBy(Long time) {
+            return time >= getValue();
+        }
+
+    }
+
+}
+
diff --git a/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/ConstraintTest.java b/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/ConstraintTest.java
index ef50d5142..de40d5578 100644
--- a/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/ConstraintTest.java
+++ b/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/ConstraintTest.java
@@ -112,6 +112,7 @@ public class ConstraintTest {
         assertThat(result, equalTo(4));
     }
 
+    @SuppressWarnings("unchecked")
     @Test
     public void theViolatedConstraintsNotifiesItsListeners() {
         final Constraint<Integer>[] constraintViolated = new Constraint[1];
diff --git a/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/DateConstraintTest.java b/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/DateConstraintTest.java
new file mode 100644
index 000000000..e22173b5e
--- /dev/null
+++ b/ganttzk/src/test/java/org/zkoss/ganttz/data/constraint/DateConstraintTest.java
@@ -0,0 +1,56 @@
+/*
+ * This file is part of ###PROJECT_NAME###
+ *
+ * Copyright (C) 2009 Fundación para o Fomento da Calidade Industrial e
+ *                    Desenvolvemento Tecnolóxico de Galicia
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.zkoss.ganttz.data.constraint;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+import java.util.Date;
+
+import org.junit.Test;
+
+public class DateConstraintTest {
+
+    private Date now = new Date();
+
+    private Constraint<Date> biggerOrEqualThanNow = DateConstraint
+            .biggerOrEqualThan(now);
+
+    @Test
+    public void canCreateConstraintBiggerThan() {
+        assertThat(biggerOrEqualThanNow.applyTo(now), equalTo(new Date(now
+                .getTime())));
+    }
+
+    @Test
+    public void biggerOrEqualThanNullLeaveValuesUnmodified() {
+        Constraint<Date> biggerThanNull = DateConstraint.biggerOrEqualThan(null);
+        Date eraStart = new Date(0);
+        assertThat(biggerThanNull.applyConstraintTo(new Date(0)),
+                equalTo(eraStart));
+    }
+
+    @Test
+    public void applyingBiggerOrEqualThanConstraintToNullNotFails() {
+        assertThat(biggerOrEqualThanNow.applyTo(null), equalTo(new Date(now
+                .getTime())));
+    }
+
+}