diff --git a/backend/index.php b/backend/index.php
index 2d70ee7..6d728ac 100644
--- a/backend/index.php
+++ b/backend/index.php
@@ -30,9 +30,10 @@ use Volkszaehler\Util;
 use Volkszaehler\Controller;
 
 // TODO replace by state class
-const VERSION = 1.1;
-const BACKEND_DIR = '/home/steffen/workspace/volkszaehler.org/backend';	// TODO realpath(__DIR__)
-const DEV_ENV = TRUE;
+define('VZ_VERSION', 0.2);
+define('VZ_DIR', '/home/steffen/workspace/volkszaehler.org');	// TODO realpath(__DIR__)
+define('BACKEND_DIR', VZ_DIR . '/backend');
+define('DEV_ENV', TRUE);
 
 // class autoloading
 require BACKEND_DIR . '/lib/Util/ClassLoader.php';
diff --git a/backend/lib/Controller/ChannelController.php b/backend/lib/Controller/ChannelController.php
index 6617078..375c537 100644
--- a/backend/lib/Controller/ChannelController.php
+++ b/backend/lib/Controller/ChannelController.php
@@ -40,7 +40,7 @@ class ChannelController extends Controller {
 	 * @todo implement filters
 	 */
 	public function get() {
-		$dql = 'SELECT c FROM Volkszaehler\Model\Channel c';
+		$dql = 'SELECT c, p FROM Volkszaehler\Model\Channel c LEFT JOIN c.properties p';
 
 		if ($uuid = $this->view->request->getParameter('uuid')) {
 			// TODO add conditions
diff --git a/backend/lib/Model/Channel.php b/backend/lib/Model/Channel.php
index 47f8c59..3698e3d 100644
--- a/backend/lib/Model/Channel.php
+++ b/backend/lib/Model/Channel.php
@@ -44,30 +44,11 @@ class Channel extends Entity {
 	protected $groups;
 
 	/**
-	 * indicator => interpreter, unit mapping
-	 *
-	 * @todo replace by properties?
+	 * Constructor
 	 */
-	protected static $indicators = array(
-		'power' =>			array('meter', 'W'),
-		'gas' =>			array('meter', 'm³'),
-		'water' =>			array('meter', 'm³'),
-		'temperature' =>	array('sensor', '°C'),
-		'pressure' =>		array('sensor', 'hPa'),
-		'humidity' =>		array('sensor', '%')
-	);
+	public function __construct($properties = array()) {
+		parent::__construct($properties);
 
-	/**
-	 * constructor
-	 */
-	public function __construct($indicator) {
-		parent::__construct();
-
-		if (!in_array($indicator, array_keys(self::$indicators))) {
-			throw new \Exception($indicator . ' is no known indicator');
-		}
-
-		$this->indicator = $indicator;
 		$this->data = new ArrayCollection();
 		$this->groups = new ArrayCollection();
 	}
@@ -118,10 +99,6 @@ class Channel extends Entity {
 	public function setResolution($resolution) { $this->resolution = $resolution; }
 	public function getCost() { return $this->cost; }
 	public function setCost($cost) { $this->cost = $cost; }
-
-	public function getType() { return self::$indicators[$this->indicator][0]; }
-	public function getUnit() { return self::$indicators[$this->indicator][1]; }
-	public function getIndicator() { return $this->indicator; }
 }
 
 ?>
diff --git a/backend/lib/Model/Entity.php b/backend/lib/Model/Entity.php
index d869c37..eee07be 100644
--- a/backend/lib/Model/Entity.php
+++ b/backend/lib/Model/Entity.php
@@ -46,7 +46,7 @@ abstract class Entity {
 	 */
 	protected $id;
 
-	/** @Column(type="string", length=36, nullable=false) */
+	/** @Column(type="string", length=36, nullable=false, unique=true) */
 	protected $uuid;
 
 	/**
@@ -56,41 +56,99 @@ abstract class Entity {
 
 	/**
 	 * @OneToMany(targetEntity="Property", mappedBy="entity")
-	 * @OrderBy({"key" = "ASC"})
+	 * @OrderBy({"name" = "ASC"})
 	 */
 	protected $properties = NULL;
 
-	public function __construct() {
+	/**
+	 * Constructor
+	 *
+	 * @param array $properties of Model\Property
+	 */
+	public function __construct($properties = array()) {
 		$this->uuid = Util\UUID::mint();
 		$this->tokens = new Collections\ArrayCollection();
 		$this->properties = new Collections\ArrayCollection();
 	}
 
 	/**
-	 *
-	 * @param unknown_type $token
+	 * Getter & setter
 	 */
-	public function validateToken($token) {
-
-	}
-
-	public function getToken() {
-
-	}
 
+	/**
+	 *
+	 * @param string $name
+	 * @return Model\Property
+	 */
 	public function getProperty($name) {
 
 	}
 
-	public function setProperty($name) {
+	public function getProperties() {
+		return $this->properties;
+	}
+
+	public function setProperty($name, $value) {
+
+	}
+
+	public function unsetProperty($name) {
 
 	}
 
-	/**
-	 * Getter & setter
-	 */
 	public function getId() { return $this->id; }		// read only
 	public function getUuid() { return $this->uuid; }	// read only
 }
 
+class EntityDefiniton extends Util\JSONDefinition {
+	/**
+	 * File containing the JSON definitons
+	 *
+	 * @var string
+	 */
+	const FILE = '/share/entities.json';
+
+	/**
+	 * List of required properties
+	 * Allowed properties = optional + required
+	 * @var array
+	 */
+	protected $required = array();
+
+	/**
+	 * List of optional properties
+	 * Allowed properties = optional + required
+	 * @var array
+	 */
+	protected $optional = array();
+
+	/**
+	 * Classname of intepreter (see backend/lib/Interpreter/)
+	 * @var string
+	 */
+	protected $interpreter;
+
+	/**
+	 * Not required for group entity
+	 * @var string
+	 */
+	protected $unit;
+
+	/**
+	 * @todo url relative or absolute?
+	 * @var string
+	 */
+	protected $icon;
+
+	/**
+	 * Check for required and optional properties
+	 *
+	 * @return boolean
+	 */
+	public function checkProperties() {
+
+	}
+
+}
+
 ?>
diff --git a/backend/lib/Model/Group.php b/backend/lib/Model/Group.php
index bcd6513..5ac2968 100644
--- a/backend/lib/Model/Group.php
+++ b/backend/lib/Model/Group.php
@@ -61,10 +61,10 @@ class Group extends Entity {
 	protected $parents = NULL;
 
 	/**
-	 * construct
+	 * Construct
 	 */
-	public function __construct() {
-		parent::__construct();
+	public function __construct($properties = array()) {
+		parent::__construct($properties);
 
 		$this->channels = new ArrayCollection();
 		$this->children = new ArrayCollection();
@@ -72,7 +72,7 @@ class Group extends Entity {
 	}
 
 	/**
-	 * adds group as new child
+	 * Adds group as new child
 	 *
 	 * @param Group $child
 	 * @todo check against endless recursion
@@ -88,7 +88,7 @@ class Group extends Entity {
 	}
 
 	/**
-	 * adds channel as new child
+	 * Adds channel as new child
 	 *
 	 * @param Channel $child
 	 * @todo check if the channel is already member of the group
@@ -103,7 +103,7 @@ class Group extends Entity {
 	}
 
 	/**
-	 * getter & setter
+	 * Getter & setter
 	 *
 	 * @todo change to new property model
 	 */
diff --git a/backend/lib/Model/Property.php b/backend/lib/Model/Property.php
index 9c094ad..8df15d6 100644
--- a/backend/lib/Model/Property.php
+++ b/backend/lib/Model/Property.php
@@ -23,6 +23,7 @@
 
 namespace Volkszaehler\Model;
 
+use Volkszaehler\Util;
 use Volkszaehler\Model;
 
 /**
@@ -53,6 +54,15 @@ class Property {
 	/** @ManyToOne(targetEntity="Entity", inversedBy="properties") */
 	protected $entity;
 
+	/**
+	 * Property definition
+	 *
+	 * Used to validate
+	 *
+	 * @var Model\PropertyDefinition
+	 */
+	protected $definition;
+
 	/**
 	 * Constructor
 	 *
@@ -60,8 +70,106 @@ class Property {
 	 * @param string $value
 	 */
 	public function __construct($name, $value) {
-		$this->name = (string) $name;
-		$this->value = (string) $value;
+		$this->definition = Model\PropertyDefinition::get($name);
+
+		$this->setName($name);
+		$this->setValue($value);
+	}
+
+	/*
+	 * Setter & Getter
+	 */
+
+	public function getName() { return $this->name; }
+	public function getValue() { return $this->value; }
+
+	public function setValue($value) {
+		if (!$this->definition->validate($value)) {
+			throw new \Exception('invalid property value'); $this->value = $value;
+		}
+	}
+
+	/**
+	 *
+	 * @param string $name
+	 * @todo validation
+	 */
+	protected function setName($name) { $this->name = $name; }
+}
+
+class PropertyDefinition extends Util\JSONDefinition {
+	/** One of: string, numeric, multiple */
+	public $type;
+
+	/**
+	 * Regex pattern to match if type == string
+	 *
+	 * @var string
+	 */
+	protected $pattern;
+
+	/**
+	 * Minimal value if type == numeric
+	 * Required string length if type == string
+	 *
+	 * @var integer|float
+	 */
+	protected $min;
+
+	/**
+	 * Maximal value if type == numeric
+	 * Allowed string length if type == string
+	 *
+	 * @var integer|float
+	 */
+	protected $max;
+
+	/**
+	 * List of possible choices if type == multiple
+	 * (type as in javascript: 1.2 => numeric, "test" => string)
+	 *
+	 * @var array
+	 */
+	protected $choices = array();
+
+
+	/**
+	 * File containing the JSON definitons
+	 *
+	 * @var string
+	 */
+	const FILE = '/share/properties.json';
+
+	/**
+	 * Validate value according to $this->type
+	 *
+	 * @param mixed $value
+	 * @return boolean
+	 */
+	public function validate($value) {
+		switch ($this->type) {
+			case 'string':
+				$invalid = !is_string($value);
+				$invalid |= isset($this->pattern) && !preg_match($this->pattern, $value);
+				$invalid |= isset($this->min) && strlen($value) < $this->min;
+				$invalid |= isset($this->max) && strlen($value) > $this->max;
+				break;
+
+			case 'numeric':
+				$invalid = !is_numeric($value);
+				$invalid |= isset($this->min) && $value < $this->min;
+				$invalid |= isset($this->max) && $value > $this->max;
+				break;
+
+			case 'multiple':
+				$invalid = !in_array($value, $this->choices, TRUE);
+				break;
+
+			default:
+				throw new \Exception('unknown property type');
+		}
+
+		return !$invalid;
 	}
 }
 
diff --git a/backend/lib/Model/Proxies/VolkszaehlerModelChannelProxy.php b/backend/lib/Model/Proxies/VolkszaehlerModelChannelProxy.php
index c35fc9b..a573b88 100644
--- a/backend/lib/Model/Proxies/VolkszaehlerModelChannelProxy.php
+++ b/backend/lib/Model/Proxies/VolkszaehlerModelChannelProxy.php
@@ -87,46 +87,28 @@ class VolkszaehlerModelChannelProxy extends \Volkszaehler\Model\Channel implemen
         return parent::setCost($cost);
     }
 
-    public function getType()
-    {
-        $this->_load();
-        return parent::getType();
-    }
-
-    public function getUnit()
-    {
-        $this->_load();
-        return parent::getUnit();
-    }
-
-    public function getIndicator()
-    {
-        $this->_load();
-        return parent::getIndicator();
-    }
-
-    public function validateToken($token)
-    {
-        $this->_load();
-        return parent::validateToken($token);
-    }
-
-    public function getToken()
-    {
-        $this->_load();
-        return parent::getToken();
-    }
-
     public function getProperty($name)
     {
         $this->_load();
         return parent::getProperty($name);
     }
 
-    public function setProperty($name)
+    public function getProperties()
     {
         $this->_load();
-        return parent::setProperty($name);
+        return parent::getProperties();
+    }
+
+    public function setProperty($name, $value)
+    {
+        $this->_load();
+        return parent::setProperty($name, $value);
+    }
+
+    public function unsetProperty($name)
+    {
+        $this->_load();
+        return parent::unsetProperty($name);
     }
 
     public function getId()
diff --git a/backend/lib/Model/Proxies/VolkszaehlerModelEntityProxy.php b/backend/lib/Model/Proxies/VolkszaehlerModelEntityProxy.php
index ce51a1d..2676536 100644
--- a/backend/lib/Model/Proxies/VolkszaehlerModelEntityProxy.php
+++ b/backend/lib/Model/Proxies/VolkszaehlerModelEntityProxy.php
@@ -27,28 +27,28 @@ class VolkszaehlerModelEntityProxy extends \Volkszaehler\Model\Entity implements
     }
 
     
-    public function validateToken($token)
-    {
-        $this->_load();
-        return parent::validateToken($token);
-    }
-
-    public function getToken()
-    {
-        $this->_load();
-        return parent::getToken();
-    }
-
     public function getProperty($name)
     {
         $this->_load();
         return parent::getProperty($name);
     }
 
-    public function setProperty($name)
+    public function getProperties()
     {
         $this->_load();
-        return parent::setProperty($name);
+        return parent::getProperties();
+    }
+
+    public function setProperty($name, $value)
+    {
+        $this->_load();
+        return parent::setProperty($name, $value);
+    }
+
+    public function unsetProperty($name)
+    {
+        $this->_load();
+        return parent::unsetProperty($name);
     }
 
     public function getId()
diff --git a/backend/lib/Model/Proxies/VolkszaehlerModelGroupProxy.php b/backend/lib/Model/Proxies/VolkszaehlerModelGroupProxy.php
index dea59e7..feee410 100644
--- a/backend/lib/Model/Proxies/VolkszaehlerModelGroupProxy.php
+++ b/backend/lib/Model/Proxies/VolkszaehlerModelGroupProxy.php
@@ -99,28 +99,28 @@ class VolkszaehlerModelGroupProxy extends \Volkszaehler\Model\Group implements \
         return parent::getInterpreter($em);
     }
 
-    public function validateToken($token)
-    {
-        $this->_load();
-        return parent::validateToken($token);
-    }
-
-    public function getToken()
-    {
-        $this->_load();
-        return parent::getToken();
-    }
-
     public function getProperty($name)
     {
         $this->_load();
         return parent::getProperty($name);
     }
 
-    public function setProperty($name)
+    public function getProperties()
     {
         $this->_load();
-        return parent::setProperty($name);
+        return parent::getProperties();
+    }
+
+    public function setProperty($name, $value)
+    {
+        $this->_load();
+        return parent::setProperty($name, $value);
+    }
+
+    public function unsetProperty($name)
+    {
+        $this->_load();
+        return parent::unsetProperty($name);
     }
 
     public function getId()
diff --git a/backend/lib/Model/Proxies/VolkszaehlerModelPropertyProxy.php b/backend/lib/Model/Proxies/VolkszaehlerModelPropertyProxy.php
index 68cd655..42860e1 100644
--- a/backend/lib/Model/Proxies/VolkszaehlerModelPropertyProxy.php
+++ b/backend/lib/Model/Proxies/VolkszaehlerModelPropertyProxy.php
@@ -27,6 +27,24 @@ class VolkszaehlerModelPropertyProxy extends \Volkszaehler\Model\Property implem
     }
 
     
+    public function getName()
+    {
+        $this->_load();
+        return parent::getName();
+    }
+
+    public function getValue()
+    {
+        $this->_load();
+        return parent::getValue();
+    }
+
+    public function setValue($value)
+    {
+        $this->_load();
+        return parent::setValue($value);
+    }
+
 
     public function __sleep()
     {
diff --git a/backend/lib/Model/Token.php b/backend/lib/Model/Token.php
index e32cc5c..7fc973f 100644
--- a/backend/lib/Model/Token.php
+++ b/backend/lib/Model/Token.php
@@ -55,7 +55,7 @@ class Token {
 	 * var integer timestamp until token is valid
 	 *
 	 * @Column(type="bigint")
-	 * @todo implement
+	 * @todo to be implemented
 	 */
 	protected $valid;
 
diff --git a/backend/lib/Util/Debug.php b/backend/lib/Util/Debug.php
index 7c0b219..108cea4 100644
--- a/backend/lib/Util/Debug.php
+++ b/backend/lib/Util/Debug.php
@@ -78,8 +78,8 @@ class Debug implements Logging\SQLLogger {
 	 * @param string $sql the sql query
 	 * @param array $parameters optional parameters for prepared queries
 	 */
-	function logSQL($sql, array $parameters = NULL) {
-		$this->queries[] = array('sql' => $sql, 'parameters' => $parameters);
+	function logSQL($sql, array $parameters = NULL, $executionMS = null) {
+		$this->queries[] = array('sql' => $sql, 'parameters' => $parameters, 'execution' => round($executionMS, 5));
 	}
 
 	/*
diff --git a/backend/lib/Util/JSON.php b/backend/lib/Util/JSON.php
new file mode 100644
index 0000000..58b4050
--- /dev/null
+++ b/backend/lib/Util/JSON.php
@@ -0,0 +1,161 @@
+<?php
+/**
+ * @author Steffen Vogel <info@steffenvogel.de>
+ * @copyright Copyright (c) 2010, The volkszaehler.org project
+ * @license http://www.gnu.org/licenses/gpl.txt GNU Public License
+ */
+/*
+ * This file is part of volkzaehler.org
+ *
+ * volkzaehler.org is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * volkzaehler.org 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace Volkszaehler\Util;
+
+/**
+ * Custom option constant for JSON::encode()
+ */
+define('JSON_PRETTY', 32);
+
+/**
+ * Static JSON utility class
+ *
+ * @package util
+ * @author Steffen Vogel <info@steffenvogel.de>
+ */
+class JSON extends \ArrayObject {
+	/**
+	 * OOP wrapper and factory
+	 * @param string $json
+	 * @return Util\JSON
+	 */
+	static public function decode($json, $assoc = false, $depth = 512) {
+		$data = json_decode(self::strip($json), $assoc, $depth);
+
+		if (is_null($data)) {
+			throw new JSONException();
+		}
+
+		return new self($data);
+	}
+
+	/**
+	 * OOP wrapper
+	 * @param integer $options use JSON_* constants
+	 * @return string the JSON encoded string
+	 */
+	public function encode($options = 0) {
+		$json = json_encode($this->getArrayCopy(), $options);
+
+		if ($options & JSON_PRETTY) {
+			$json = self::format($json);
+		}
+
+		return $json;
+	}
+
+	public function __toString() {
+		return $this->encode();
+	}
+
+	protected static function format($json, $indent = "\t", $newLine = "\n") {
+		$formatted = '';
+		$indentLevel = 0;
+		$inString = FALSE;
+
+		$len = strlen($json);
+		for($c = 0; $c < $len; $c++) {
+			$char = $json[$c];
+			switch($char) {
+				case '{':
+				case '[':
+					$formatted .= $char;
+					if (!$inString && (ord($json[$c+1]) != ord($char)+2)) {
+						$indentLevel++;
+						$formatted .= $newLine . str_repeat($indent, $indentLevel);
+					}
+					break;
+				case '}':
+				case ']':
+					if (!$inString && (ord($json[$c-1]) != ord($char)-2)) {
+						$indentLevel--;
+						$formatted .= $newLine . str_repeat($indent, $indentLevel);
+					}
+					$formatted .= $char;
+					break;
+				case ',':
+					$formatted .= $char;
+					if (!$inString) {
+						$formatted .= $newLine . str_repeat($indent, $indentLevel);
+					}
+					break;
+				case ':':
+					$formatted .= $char;
+					if (!$inString) {
+						$formatted .= ' ';
+					}
+					break;
+				case '"':
+					if ($c > 0 && $json[$c-1] != '\\') {
+						$inString = !$inString;
+					}
+				default:
+					$formatted .= $char;
+					break;
+			}
+		}
+
+		return $formatted;
+	}
+
+	/**
+	 * Strip whitespaces and comments from JSON string
+	 *
+	 * Nessecary for parsing a JSON string with json_decode()
+	 *
+	 * @param string $json
+	 */
+	protected static function strip($json) {
+		$json = preg_replace(array(
+			// eliminate single line comments in '// ...' form
+			'#//(.+)$#m',
+
+			// eliminate multi-line comments in '/* ... */' form
+			'#/\*.*?\*/#s'
+		), '', $json);
+
+		// eliminate extraneous space
+		return trim($json);
+	}
+}
+
+class JSONException extends \Exception {
+	/**
+	 * @var array errorcodes defined by json_last_error()
+	 */
+	protected static $errors = array(
+		JSON_ERROR_NONE => 'No error has occurred',
+		JSON_ERROR_DEPTH => 'The maximum stack depth has been exceeded',
+		JSON_ERROR_CTRL_CHAR => 'Control character error, possibly incorrectly encoded',
+		JSON_ERROR_STATE_MISMATCH => 'Invalid or malformed JSON',
+		JSON_ERROR_SYNTAX => 'Syntax error',
+		JSON_ERROR_UTF8 => 'Malformed UTF-8 characters, possibly incorrectly encoded'
+	);
+
+	public function __construct($message = NULL, $code = 0) {
+		parent::__construct((is_null($message)) ? self::$errors[json_last_error()] : $message, $code);
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/backend/lib/Util/JSONDefinition.php b/backend/lib/Util/JSONDefinition.php
new file mode 100644
index 0000000..515dd53
--- /dev/null
+++ b/backend/lib/Util/JSONDefinition.php
@@ -0,0 +1,96 @@
+<?php
+/**
+ * @copyright Copyright (c) 2010, The volkszaehler.org project
+ * @package util
+ * @license http://www.gnu.org/licenses/gpl.txt GNU Public License
+ */
+/*
+ * This file is part of volkzaehler.org
+ *
+ * volkzaehler.org is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * volkzaehler.org 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace Volkszaehler\Util;
+
+/**
+ * @author Steffen Vogel <info@steffenvogel.de>
+ * @package util
+ */
+abstract class JSONDefinition {
+	/**
+	 * Cached json definitions
+	 *
+	 * @var array
+	 */
+	protected static $definitions = NULL;
+
+	/** Discriminator for database column */
+	protected $name;
+
+	/**
+	 * Hide default constructor
+	 *
+	 * @param array $name
+	 */
+	protected function __construct($object) {
+		foreach (get_object_vars($object) as $name => $value) {
+			if (property_exists(get_class($this), $name)) {
+				$this->$name = $value;
+			}
+			else {
+				throw new \Exception('unknown definition: ' . $name);
+			}
+		}
+	}
+
+
+	/**
+	 * Factory method for creating new instances
+	 *
+	 * @param string $name
+	 * @return Model\PropertyDefinition
+	 */
+	public static function get($name) {
+		if (is_null(self::$definitions)) {
+			self::load();
+		}
+
+		if (!isset(self::$definitions[$name])) {
+			throw new \Exception('unknown definition');
+		}
+
+		return self::$definitions[$name];
+	}
+
+	/**
+	 * Load JSON definitions from file (via lazy loading from get())
+	 */
+	protected static function load() {
+		$json = file_get_contents(VZ_DIR . static::FILE);
+		$json = JSON::strip($json);
+		$json = json_decode($json);	// TODO move to Util\JSON class
+
+		if (!is_array($json) || count($json) == 0) {
+			throw new \Exception('syntax error in definition');
+		}
+
+		self::$definitions = array();
+
+		foreach ($json as $property) {
+			self::$definitions[$property->name] = new static($property);
+		}
+	}
+}
+
+?>
\ No newline at end of file
diff --git a/backend/lib/View/CSV.php b/backend/lib/View/CSV.php
index 7c8d867..9deba2b 100644
--- a/backend/lib/View/CSV.php
+++ b/backend/lib/View/CSV.php
@@ -46,7 +46,7 @@ class CSV extends View {
 		parent::__construct($request, $response);
 
 		echo 'source: volkszaehler.org' . PHP_EOL;
-		echo 'version: ' . \Volkszaehler\VERSION . PHP_EOL;
+		echo 'version: ' . VZ_VERSION . PHP_EOL;
 
 		$this->response->setHeader('Content-type', 'text/csv');
 		$this->response->setHeader('Content-Disposition', 'attachment; filename="data.csv"');
diff --git a/backend/lib/View/JSON.php b/backend/lib/View/JSON.php
index 0ba27df..d8b5c10 100644
--- a/backend/lib/View/JSON.php
+++ b/backend/lib/View/JSON.php
@@ -34,7 +34,7 @@ use Volkszaehler\Model;
  * @author Steffen Vogel <info@steffenvogel.de>
  */
 class JSON extends View {
-	protected $json = array();
+	protected $json;
 
 	protected $padding = FALSE;
 
@@ -44,8 +44,10 @@ class JSON extends View {
 	public function __construct(HTTP\Request $request, HTTP\Response $response) {
 		parent::__construct($request, $response);
 
+		$this->json = new Util\JSON();
+
 		$this->json['source'] = 'volkszaehler.org';
-		$this->json['version'] = \Volkszaehler\VERSION;
+		$this->json['version'] = VZ_VERSION;
 
 		$this->response->setHeader('Content-type', 'application/json');
 
@@ -56,15 +58,10 @@ class JSON extends View {
 
 	public function addChannel(Model\Channel $channel, array $data = NULL) {
 		$jsonChannel['uuid'] = (string) $channel->getUuid();
-		$jsonChannel['type'] = $channel->getType();
-		$jsonChannel['indicator'] = $channel->getIndicator();
-		$jsonChannel['unit'] = $channel->getUnit();
-		$jsonChannel['name'] = $channel->getName();
-		$jsonChannel['description'] = $channel->getDescription();
 
-		if ($channel->getType() == 'meter') {
-			$jsonChannel['resolution'] = (int) $channel->getResolution();
-			$jsonChannel['cost'] = (float) $channel->getCost();
+
+		foreach ($channel->getProperties() as $property) {
+			$jsonChannel[$property->getName()] = $property->getValue();
 		}
 
 		if (isset($data)) {
@@ -138,11 +135,7 @@ class JSON extends View {
 	}
 
 	public function renderResponse() {
-		$json = json_encode($this->json);
-
-		if (Util\Debug::isActivated()) {
-			$json = self::format($json);
-		}
+		$json = $this->json->encode((Util\Debug::isActivated()) ? JSON_PRETTY : 0);
 
 		if ($this->padding) {
 			$json = 'if (self.' . $this->padding . ') { ' . $this->padding  . '(' . $json . '); }';
@@ -150,56 +143,6 @@ class JSON extends View {
 
 		echo $json;
 	}
-
-	protected static function format($json) {
-		$formatted = '';
-		$indentLevel = 0;
-		$inString = FALSE;
-
-		$len = strlen($json);
-		for($c = 0; $c < $len; $c++) {
-			$char = $json[$c];
-			switch($char) {
-				case '{':
-				case '[':
-					$formatted .= $char;
-					if (!$inString && (ord($json[$c+1]) != ord($char)+2)) {
-						$indentLevel++;
-						$formatted .= "\n" . str_repeat("\t", $indentLevel);
-					}
-					break;
-				case '}':
-				case ']':
-					if (!$inString && (ord($json[$c-1]) != ord($char)-2)) {
-						$indentLevel--;
-						$formatted .= "\n" . str_repeat("\t", $indentLevel);
-					}
-					$formatted .= $char;
-					break;
-				case ',':
-					$formatted .= $char;
-					if (!$inString) {
-						$formatted .= "\n" . str_repeat("\t", $indentLevel);
-					}
-					break;
-				case ':':
-					$formatted .= $char;
-					if (!$inString) {
-						$formatted .= ' ';
-					}
-					break;
-				case '"':
-					if ($c > 0 && $json[$c-1] != '\\') {
-						$inString = !$inString;
-					}
-				default:
-					$formatted .= $char;
-					break;
-			}
-		}
-
-		return $formatted;
-	}
 }
 
 ?>
\ No newline at end of file
diff --git a/backend/lib/View/PlainText.php b/backend/lib/View/PlainText.php
index f0800cd..0656fc8 100644
--- a/backend/lib/View/PlainText.php
+++ b/backend/lib/View/PlainText.php
@@ -41,7 +41,7 @@ class PlainText extends View {
 		parent::__construct($request, $response);
 
 		echo 'source: volkszaehler.org' . PHP_EOL;
-		echo 'version: ' . \Volkszaehler\VERSION . PHP_EOL;
+		echo 'version: ' . VZ_VERSION . PHP_EOL;
 
 		$this->response->setHeader('Content-type', 'text/plain');
 	}
diff --git a/backend/lib/View/XML.php b/backend/lib/View/XML.php
index 18b60f1..35147d1 100644
--- a/backend/lib/View/XML.php
+++ b/backend/lib/View/XML.php
@@ -47,7 +47,7 @@ class XML extends View {
 		$this->xmlRoot = $this->xmlDoc->createElement('volkszaehler');
 		$this->xmlDoc->appendChild($this->xmlRoot);
 
-		$this->xmlRoot->setAttribute('version', \Volkszaehler\VERSION);
+		$this->xmlRoot->setAttribute('version', VZ_VERSION);
 		$this->xmlRoot->setAttribute('source', 'volkszaehler.org');
 
 		$this->response->setHeader('Content-type', 'application/xml; charset=UTF-8');
diff --git a/share/entities.json b/share/entities.json
index 8725d46..74864fc 100644
--- a/share/entities.json
+++ b/share/entities.json
@@ -1,5 +1,7 @@
 /**
  * Definition of entities 
+ 
+ * Format is specified in EntityDefinition class
  *
  * @author Steffen Vogel <info@steffenvogel.de>
  * @copyright Copyright (c) 2010, The volkszaehler.org project
@@ -22,87 +24,83 @@
  * You should have received a copy of the GNU General Public License
  * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
  */
- 
-{	
-	"entities" : [
-		/*{
-			"name" : "",				// discriminator for database column
-			"required" : [],			// list of required properties
-			"optional" : [],			// list of optional properties
-										// allowed properties = optional + required
-			"interpreter" : "",			// classname of intepreter (see backend/lib/Interpreter/)
-			"unit" : "",				// not required for group
-			"icon" : ""				// TODO url relative or absolute?
-		}*/
-		{
-			"name" : "group",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "tolerance"],
-			"interpreter" : "GroupInterpreter",
-			"icon" : ""				// TODO look for an group icon
-		},
-		{
-			"name" : "power",
-			"required" : ["name", "resolution"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "MeterInterpreter",
-			"icon" : ""				// TODO look for an power icon
-		},
-		{
-			"name" : "gas",
-			"required" : ["name", "resolution"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "MeterInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "rainfall",
-			"required" : ["name", "resolution"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "MeterInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "temperature",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "pressure",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "humidity",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "windspeed",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "radition",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-		{
-			"name" : "luminosity",
-			"required" : ["name"],
-			"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
-			"interpreter" : "SensorInterpreter",
-			"icon" : ""				// TODO look for an water icon
-		},
-	]
-}
\ No newline at end of file
+
+[
+	{
+		"name" : "group",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "tolerance"],
+		"interpreter" : "GroupInterpreter",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "power",
+		"required" : ["name", "resolution"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "MeterInterpreter",
+		"unit" : "kW/h",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "gas",
+		"required" : ["name", "resolution"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "MeterInterpreter",
+		"unit" : "m³/h",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "water",
+		"required" : ["name", "resolution"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "MeterInterpreter",
+		"unit" : "m³/h",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "temperature",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"unit" : "°C",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "pressure",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"unit" : "hPa",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "humidity",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"unit" : "%",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "windspeed",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"unit" : "km/h",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "radition",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"icon" : ""					// TODO look for an icon
+	},
+	{
+		"name" : "luminosity",
+		"required" : ["name"],
+		"optional" : ["description", "details:", "owner:", "address:", "tolerance"],
+		"interpreter" : "SensorInterpreter",
+		"icon" : ""					// TODO look for an icon
+	},
+]
diff --git a/share/properties.json b/share/properties.json
index 68c3726..ead82fc 100644
--- a/share/properties.json
+++ b/share/properties.json
@@ -1,5 +1,7 @@
 /**
- * Definition of properties for entities 
+ * Definition of properties for entities
+ *
+ * Format is specified in PropertyDefinition class
  *
  * @author Steffen Vogel <info@steffenvogel.de>
  * @copyright Copyright (c) 2010, The volkszaehler.org project
@@ -23,84 +25,72 @@
  * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
  */
 
-{
-	"properties" : [
-		/*{
-			"name" : "",				// discriminator for database column
-			"type" : "",				// one of: string, numeric, multiple
-			"pattern" : "",				// regex pattern to match if type == string
-			"min" : 0,					// minimal value if type == numeric
-										// required string length if type == string
-			"max" : 100,				// maximal value if type == numeric
-										// allowed string length if type == string
-			"choices" : ["", "", ""]	// list of possible choices if type == multiple
-										// (type as in javascript: 1.2 => numeric, "test" => string)
-		},*/
-		{
-			"name" : "name",
-			"type" : "string",
-			"pattern" : "/[a-z0-9 ]/",
-			"max" : 255,
-		},
-		{
-			"name" : "description",
-			"type" : "string",
-			"pattern" : "/[a-z0-9 ]/",	// TODO add whitespaces as \t \n \r
-			"max" : 255,				// TODO allowed column size in database?
-		},
-		{
-			"name" : "cost",
-			"type" : "numeric",
-			"min" : 0,
-		},
-		{
-			"name" : "resolution",
-			"type" : "numeric",
-			"min" : 1,
-		},
-		{
-			"name" : "tolerance",
-			"type" : "numeric",
-			"min" : 0,
-			"max" : 1
-		},
-		{
-			"name" : "address:lat",
-			"type" : "numeric",
-			"min" : -90,
-			"max" : 90
-		},
-		{
-			"name" : "address:lon",
-			"type" : "numeric",
-			"min" : -90,
-			"max" : 90
-		},
-		{
-			"name" : "address:city",
-			"type" : "string",
-			"pattern" : ""				// TODO add pattern
-		},
-		{
-			"name" : "address:houseno",
-			"type" : "string"
-		},
-		{
-			"name" : "address:postal",
-			"type" : "string"
-		},
-		{
-			"name" : "address:state",
-			"type" : "string"
-		},
-		{
-			"name" : "address:country",
-			"type" : "string"
-		},
-		{
-			"name" : "photo:url",
-			"type" : "string",
-			"pattern" : ""				// TODO add pattern
-		},
-	]
-}
\ No newline at end of file
+[
+	{
+		"name" : "name",
+		"type" : "string",
+		"pattern" : "/[a-z0-9 ]/",
+		"min": 3,
+		"max" : 255
+	},
+	{
+		"name" : "description",
+		"type" : "string",
+		"pattern" : "/[a-z0-9 ]/",	// TODO add whitespaces as \t \n \r
+		"max" : 255					// TODO allowed column size in database?
+	},
+	{
+		"name" : "cost",
+		"type" : "numeric",
+		"min" : 0
+	},
+	{
+		"name" : "resolution",
+		"type" : "numeric",
+		"min" : 1
+	},
+	{
+		"name" : "tolerance",
+		"type" : "numeric",
+		"min" : 0,
+		"max" : 1
+	},
+	{
+		"name" : "address:lat",
+		"type" : "numeric",
+		"min" : -90,
+		"max" : 90
+	},
+	{
+		"name" : "address:lon",
+		"type" : "numeric",
+		"min" : -90,
+		"max" : 90
+	},
+	{
+		"name" : "address:city",
+		"type" : "string",
+		"pattern" : ""				// TODO add pattern
+	},
+	{
+		"name" : "address:houseno",
+		"type" : "string"
+	},
+	{
+		"name" : "address:postal",
+		"type" : "string"
+	},
+	{
+		"name" : "address:state",
+		"type" : "string"
+	},
+	{
+		"name" : "address:country",
+		"type" : "string"
+	},
+	{
+		"name" : "photo:url",
+		"type" : "string",
+		"pattern" : ""				// TODO add pattern
+	}
+]
diff --git a/share/tests/json.php b/share/tests/json.php
new file mode 100644
index 0000000..47396bd
--- /dev/null
+++ b/share/tests/json.php
@@ -0,0 +1,62 @@
+<?php
+/**
+ * A test for our JSON utility class
+ *
+ * @package tests
+ * @copyright Copyright (c) 2010, The volkszaehler.org project
+ * @license http://www.gnu.org/licenses/gpl.txt GNU Public License
+ * @author Steffen Vogel <info@steffenvogel.de>
+ */
+/*
+ * This file is part of volkzaehler.org
+ *
+ * volkzaehler.org is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * volkzaehler.org 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use Volkszaehler\Util;
+include '../../backend/lib/Util/JSON.php';
+echo '<pre>';
+
+$data = '{
+    "glossary": {
+        "title": "example glossary",
+		"GlossDiv": {
+            "title": "S",
+			"GlossList": {
+                "GlossEntry": {
+                    "ID": "SGML",
+					"SortAs": "SGML",
+					"GlossTerm": "Standard Generalized Markup Language",
+					"Acronym": "SGML",
+					"Abbrev": "ISO 8879:1986",
+					"GlossDef": {
+                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
+						"GlossSeeAlso": ["GML", "XML"]
+                    },
+					"GlossSee": "markup"
+                }
+            }
+        }
+    }
+}';
+
+$json = Util\JSON::decode($data);
+
+$json['test'] = 2;
+
+echo $json->encode(JSON_PRETTY);
+
+
+echo '</pre>';
+?>
\ No newline at end of file
diff --git a/share/tests/properties.php b/share/tests/properties.php
new file mode 100644
index 0000000..5d0d7b1
--- /dev/null
+++ b/share/tests/properties.php
@@ -0,0 +1,41 @@
+<?php
+/**
+ * A test for our Property class
+ *
+ * @package tests
+ * @copyright Copyright (c) 2010, The volkszaehler.org project
+ * @license http://www.gnu.org/licenses/gpl.txt GNU Public License
+ * @author Steffen Vogel <info@steffenvogel.de>
+ */
+/*
+ * This file is part of volkzaehler.org
+ *
+ * volkzaehler.org is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * any later version.
+ *
+ * volkzaehler.org 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with volkszaehler.org. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use Volkszaehler\Util;
+use Volkszaehler\Model;
+
+define('VZ_DIR', '/home/steffen/workspace/volkszaehler.org');	// TODO realpath(__DIR__)
+
+include '../../backend/lib/Util/JSONDefinition.php';
+include '../../backend/lib/Model/Property.php';
+include '../../backend/lib/Util/JSON.php';
+
+echo '<pre>';
+
+new Model\Property('name', '1as2');
+
+echo '</pre>';
+?>
\ No newline at end of file