diff --git a/backend/lib/Model/Definition.php b/backend/lib/Model/Definition.php
index 2edd2c8..737b79b 100644
--- a/backend/lib/Model/Definition.php
+++ b/backend/lib/Model/Definition.php
@@ -1,7 +1,7 @@
 <?php
 /**
  * @copyright Copyright (c) 2010, The volkszaehler.org project
- * @package util
+ * @package default
  * @license http://www.gnu.org/licenses/gpl.txt GNU Public License
  */
 /*
@@ -21,21 +21,23 @@
  * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
  */
 
-namespace Volkszaehler\Util;
+namespace Volkszaehler\Model;
+
+use Volkszaehler\Util;
 
 /**
  * @author Steffen Vogel <info@steffenvogel.de>
- * @package util
+ * @package default
  */
 abstract class Definition {
 	/** @var string discriminator for database column */
 	protected $name;
 
 	/** @var string title for UI */
-	protected $title;
+	//protected $title;
 
 	/** @var string description for UI */
-	protected $description;
+	//protected $description;
 
 	/**
 	 * Hide default constructor
@@ -84,7 +86,7 @@ abstract class Definition {
 	 * Load JSON definitions from file (via lazy loading from get())
 	 */
 	protected static function load() {
-		$json = JSON::decode(file_get_contents(VZ_DIR . static::FILE));
+		$json = Util\JSON::decode(file_get_contents(VZ_DIR . static::FILE));
 
 		static::$definitions = array();
 
diff --git a/backend/lib/Model/EntityDefinition.php b/backend/lib/Model/EntityDefinition.php
index 461d977..5901b33 100644
--- a/backend/lib/Model/EntityDefinition.php
+++ b/backend/lib/Model/EntityDefinition.php
@@ -27,7 +27,7 @@ namespace Volkszaehler;
  * @author Steffen Vogel <info@steffenvogel.de>
  * @package default
  */
-class EntityDefinition extends Util\Definition {
+class EntityDefinition extends Definition {
 	/** @var string File containing the JSON definitons */
 	const FILE = '/share/entities.json';
 
diff --git a/backend/lib/Model/Property.php b/backend/lib/Model/Property.php
index a14f352..1a1fc3d 100644
--- a/backend/lib/Model/Property.php
+++ b/backend/lib/Model/Property.php
@@ -73,6 +73,17 @@ class Property {
 		$this->entity = $entity;
 	}
 
+	/**
+	 * Cast property value according to $this->type
+	 *
+	 * @PostLoad
+	 */
+	public function castValue() {
+		if ($this->getDefinition()->getType() != 'multiple') {
+			settype($this->value, $this->getDefinition()->getType());
+		}
+	}
+
 	/**
 	 * Validate property name & value
 	 *
@@ -80,11 +91,15 @@ class Property {
 	 *
 	 * @PrePersist
 	 * @PreUpdate
-	 * @PostLoad
-	 * @todo to be implemented
 	 */
-	function validate() {
+	public function validate() {
+		if (!PropertyDefinition::exists($this->name)) {
+			throw new \Exception('invalid property name: ' . $this->name);
+		}
 
+		if (!$this->getDefinition()->validateValue($this->value)) {
+			throw new \Exception('invalid property value: ' . $this->value);
+		}
 	}
 
 	/*
@@ -94,20 +109,7 @@ class Property {
 	public function getValue() { return $this->value; }
 	public function getDefinition() { return PropertyDefinition::get($this->name); }
 
-	public function setValue($value) {
-		if (!$this->getDefinition()->validateValue($value)) {
-			throw new \Exception('invalid property value');
-		}
-
-		$this->value = $value;
-	}
-
-	/**
-	 *
-	 * @param string $name
-	 * @todo validation
-	 */
-	protected function setName($name) { $this->name = $name; }
+	public function setValue($value) { $this->value = $value; }
 }
 
 ?>
diff --git a/backend/lib/Model/PropertyDefinition.php b/backend/lib/Model/PropertyDefinition.php
index 773f086..ddaffed 100644
--- a/backend/lib/Model/PropertyDefinition.php
+++ b/backend/lib/Model/PropertyDefinition.php
@@ -23,15 +23,13 @@
 
 namespace Volkszaehler\Model;
 
-use Volkszaehler\Util;
-
 /**
  * @author Steffen Vogel <info@steffenvogel.de>
  * @package default
  */
-class PropertyDefinition extends Util\Definition {
-	/** One of: string, numeric, multiple */
-	public $type;
+class PropertyDefinition extends Definition {
+	/** One of: string, integer, float, boolean, multiple */
+	protected $type;
 
 	/** @var string regex pattern to match if type == string */
 	protected $pattern;
@@ -54,7 +52,7 @@ class PropertyDefinition extends Util\Definition {
 
 	/**
 	 * List of possible choices if type == multiple
-	 * (type as in javascript: 1.2 => float, 5 => integer, "test" => string)
+	 * (type as in javascript: 1.2 => float, 5 => integer, true => boolean, "test" => string)
 	 *
 	 * @var array
 	 */
@@ -93,6 +91,10 @@ class PropertyDefinition extends Util\Definition {
 				$invalid = !is_float($value);	// TODO check for numeric string
 				break;
 
+			case 'boolean':
+				$invalid = !is_bool($value);	// TODO check for numeric string
+				break;
+
 			case 'multiple':
 				$invalid = !in_array($value, $this->choices, TRUE);
 				break;
@@ -108,6 +110,11 @@ class PropertyDefinition extends Util\Definition {
 
 		return !$invalid;
 	}
+
+	/*
+	 * Setter & getter
+	 */
+	public function getType() { return $this->type; }
 }
 
 ?>