diff --git a/backend/bin/doctrine.php b/backend/bin/doctrine.php
index df24c7a..f30be4b 100644
--- a/backend/bin/doctrine.php
+++ b/backend/bin/doctrine.php
@@ -1,4 +1,4 @@
-<?php
+d<?php
 /**
  * doctrine cli configuration and bootstrapping
  *
@@ -80,4 +80,4 @@ $cli->addCommands(array(
 ));
 $cli->run();
 
-?>
+?>
\ No newline at end of file
diff --git a/backend/index.php b/backend/index.php
index 581b3bb..b421caf 100644
--- a/backend/index.php
+++ b/backend/index.php
@@ -54,4 +54,4 @@ $r = new Router();
 $r->run();
 $r->view->send();
 
-?>
+?>
\ No newline at end of file
diff --git a/backend/lib/Iterator/DataIterator.php b/backend/lib/Iterator/DataIterator.php
index 07dd091..9e9b122 100644
--- a/backend/lib/Iterator/DataIterator.php
+++ b/backend/lib/Iterator/DataIterator.php
@@ -33,7 +33,7 @@ class DataIterator implements \Iterator, \Countable {
 	protected $current;
 	protected $key;			// incrementing key
 	protected $stmt;		// PDOStatement
-	protected $size;	// total readings in PDOStatement
+	protected $size;		// total readings in PDOStatement
 
 	/**
 	 * Constructor
diff --git a/backend/lib/Model/Aggregator.php b/backend/lib/Model/Aggregator.php
index 893ae0a..63d58c9 100644
--- a/backend/lib/Model/Aggregator.php
+++ b/backend/lib/Model/Aggregator.php
@@ -85,7 +85,7 @@ class Aggregator extends Entity {
 	}
 
 	public function removeAggregator(Aggregator $child) {
-		$this->children->removeElement($child);
+		return $this->children->removeElement($child);
 	}
 
 	/**
@@ -93,20 +93,22 @@ class Aggregator extends Entity {
 	 *
 	 * @param Channel $child
 	 * @todo check if the channel is already member of the group
-	 * @todo add bidrection association
+	 * @todo add bidrectional association
 	 */
 	public function addChannel(Channel $child) {
 		$this->channels->add($child);
 	}
 
 	public function removeChannel(Channel $child) {
-		$this->channels->removeElement($child);
+		return $this->channels->removeElement($child);
 	}
 
-	/**
-	 * @todo return array via ArrayCollection::toArray()?
+	/*
+	 * Setter & getter
 	 */
-	public function getChannels() { return $this->channels; }
+	public function getChannels() { return $this->channels->toArray(); }
+	public function getChildren() { return $this->children->toArray(); }
 }
 
+
 ?>
\ No newline at end of file
diff --git a/backend/lib/Model/Data.php b/backend/lib/Model/Data.php
index d93e711..03b07fb 100644
--- a/backend/lib/Model/Data.php
+++ b/backend/lib/Model/Data.php
@@ -70,8 +70,7 @@ class Data {
 	 */
 	protected $channel;
 
-	public function __construct(Model\Channel $channel, $value, $timestamp) {
-		$channel->addData($this);	// bidirectional association
+	public function __construct(Model\Channel $channel, $timestamp, $value) {
 		$this->channel = $channel;
 
 		$this->value = $value;
diff --git a/backend/lib/Model/EntityDefinition.php b/backend/lib/Model/EntityDefinition.php
index c79665c..85ff2eb 100644
--- a/backend/lib/Model/EntityDefinition.php
+++ b/backend/lib/Model/EntityDefinition.php
@@ -66,7 +66,7 @@ class EntityDefinition extends Definition {
 	protected $unit;
 
 	/**
-	 * @todo url relative or absolute?
+	 * Relative url to an icon
 	 * @var string
 	 */
 	protected $icon;
diff --git a/backend/lib/Model/Token.php b/backend/lib/Model/Token.php
index 4865ad6..ae8b560 100644
--- a/backend/lib/Model/Token.php
+++ b/backend/lib/Model/Token.php
@@ -30,6 +30,7 @@ use Volkszaehler\Util;
  *
  * @author Steffen Vogel <info@steffenvogel.de>
  * @package default
+ * @todo this is a draft! has to be discussed and implemented
  *
  * @Entity
  * @Table(name="tokens")
diff --git a/backend/lib/Util/Configuration.php b/backend/lib/Util/Configuration.php
index 85a329f..7ba0935 100644
--- a/backend/lib/Util/Configuration.php
+++ b/backend/lib/Util/Configuration.php
@@ -28,6 +28,7 @@ namespace Volkszaehler\Util;
  *
  * @package util
  * @author Steffen Vogel <info@steffenvogel.de>
+ * @todo why not with json?
  */
 class Configuration {
 	static protected $values = array();
diff --git a/backend/lib/Util/Debug.php b/backend/lib/Util/Debug.php
index 0dcc55d..aa3a012 100644
--- a/backend/lib/Util/Debug.php
+++ b/backend/lib/Util/Debug.php
@@ -66,7 +66,7 @@ class Debug {
 		self::$instance = $this;
 
 		// assert options
-		assert_options(ASSERT_ACTIVE, TRUE);
+		assert_options(ASSERT_ACTIVE, TRUE);	// activate assertions
 		assert_options(ASSERT_BAIL, FALSE);
 		assert_options(ASSERT_WARNING, FALSE);
 		assert_options(ASSERT_CALLBACK, array($this, 'assertHandler'));
@@ -98,7 +98,6 @@ class Debug {
 	 * simple assertion passthrough for future improvements
 	 *
 	 * @param string $code code to be evaluated
-	 * @todo check how should be en/disabled (options etc..)
 	 */
 	public static function assert($code) {
 		return assert($code);
@@ -147,7 +146,7 @@ class Debug {
 
 	/**
 	 * @return Debug the Debug instance if available
-	 * @todo OOP? Should we remove this? Replace by State class?
+	 * @todo encapsulate in state class? or inherit from singleton class?
 	 */
 	public static function getInstance() { return self::$instance; }
 }