diff --git a/backend/lib/Controller/AggregatorController.php b/backend/lib/Controller/AggregatorController.php
index 1981bdd..17f8de6 100644
--- a/backend/lib/Controller/AggregatorController.php
+++ b/backend/lib/Controller/AggregatorController.php
@@ -55,20 +55,13 @@ class AggregatorController extends EntityController {
 
 			if ($uuid = $this->view->request->getParameter('uuid')) {
 				$ec = new EntityController($this->view, $this->em);
-				$entity = $ec->get($uuid);
-
-				if ($entity instanceof Model\Channel) {
-					$aggregator->addChannel($entity);
-				}
-				elseif ($entity instanceof Model\Aggregator) {
-					$aggregator->addAggregator($entity);
-				}
+				$aggregator->addChild($ec->get($uuid));
 			}
-			else {					// create new aggregator
+			else {
 				throw new \Exception('You have to specifiy a uuid to add');
 			}
 		}
-		else {
+		else {	// create new aggregator
 			$aggregator = new Model\Aggregator('group');	// TODO support for other aggregator types
 
 			foreach ($this->view->request->getParameters() as $parameter => $value) {
@@ -94,22 +87,15 @@ class AggregatorController extends EntityController {
 
 			if ($uuid) {
 				$ec = new EntityController($this->view, $this->em);
-				$entity = $ec->get($uuid);
-
-				if ($entity instanceof Model\Channel) {
-					$aggregator->removeChannel($entity);
-				}
-				elseif ($entity instanceof Model\Aggregator) {
-					$aggregator->removeAggregator($entity);
-				}
+				$aggregator->removeChild($ec->get($uuid));
 
 				$this->em->flush();
 			}
-			else {					// remove aggregator
+			else {
 				throw new \Exception('You have to specifiy a uuid to remove');
 			}
 		}
-		else {
+		else {	// remove aggregator
 			parent::delete($identifier);
 		}
 
diff --git a/backend/lib/Model/Aggregator.php b/backend/lib/Model/Aggregator.php
index 63d58c9..b04a9a9 100644
--- a/backend/lib/Model/Aggregator.php
+++ b/backend/lib/Model/Aggregator.php
@@ -39,28 +39,14 @@ use Doctrine\Common\Collections\ArrayCollection;
  */
 class Aggregator extends Entity {
 	/**
-	 * @ManyToMany(targetEntity="Channel", inversedBy="groups")
-	 * @JoinTable(name="groups_channel",
-	 * 		joinColumns={@JoinColumn(name="group_id", referencedColumnName="id")},
-	 * 		inverseJoinColumns={@JoinColumn(name="channel_id", referencedColumnName="id")}
-	 * )
-	 */
-	protected $channels = NULL;
-
-	/**
-	 * @ManyToMany(targetEntity="Aggregator", inversedBy="parents")
-	 * @JoinTable(name="groups_groups",
+	 * @ManyToMany(targetEntity="Entity", inversedBy="parents")
+	 * @JoinTable(name="entities_in_aggregator",
 	 * 		joinColumns={@JoinColumn(name="parent_id", referencedColumnName="id")},
 	 * 		inverseJoinColumns={@JoinColumn(name="child_id", referencedColumnName="id")}
 	 * )
 	 */
 	protected $children = NULL;
 
-	/**
-	 * @ManyToMany(targetEntity="Aggregator", mappedBy="children")
-	 */
-	protected $parents = NULL;
-
 	/**
 	 * Construct
 	 */
@@ -69,44 +55,33 @@ class Aggregator extends Entity {
 
 		$this->channels = new ArrayCollection();
 		$this->children = new ArrayCollection();
-		$this->parents = new ArrayCollection();
 	}
 
 	/**
-	 * Adds group as new child
+	 * Adds entity as new child
 	 *
-	 * @param Aggregator $child
-	 * @todo check against endless recursion
-	 * @todo check if the group is already member of the group
-	 * @todo add bidirectional association
+	 * @param Entity $child
+	 * @todo check if the entity is already member of the group
+	 * @todo add bidrectional association
 	 */
-	public function addAggregator(Aggregator $child) {
+	public function addChild(Entity $child) {
 		$this->children->add($child);
 	}
 
-	public function removeAggregator(Aggregator $child) {
-		return $this->children->removeElement($child);
-	}
-
 	/**
-	 * Adds channel as new child
+	 * Remove child from group
 	 *
-	 * @param Channel $child
-	 * @todo check if the channel is already member of the group
+	 * @param Entity $child
+	 * @todo check if the entity is member of the group
 	 * @todo add bidrectional association
 	 */
-	public function addChannel(Channel $child) {
-		$this->channels->add($child);
-	}
-
-	public function removeChannel(Channel $child) {
-		return $this->channels->removeElement($child);
+	public function removeChild(Entity $child) {
+		return $this->children->removeElement($child);
 	}
 
 	/*
 	 * Setter & getter
 	 */
-	public function getChannels() { return $this->channels->toArray(); }
 	public function getChildren() { return $this->children->toArray(); }
 }
 
diff --git a/backend/lib/Model/Entity.php b/backend/lib/Model/Entity.php
index da209bd..a50e889 100644
--- a/backend/lib/Model/Entity.php
+++ b/backend/lib/Model/Entity.php
@@ -69,6 +69,11 @@ abstract class Entity {
 	 */
 	protected $properties = NULL;
 
+	/**
+	 * @ManyToMany(targetEntity="Aggregator", mappedBy="children")
+	 */
+	protected $parents = NULL;
+
 	/**
 	 * Constructor
 	 *
@@ -84,6 +89,7 @@ abstract class Entity {
 
 		$this->tokens = new Collections\ArrayCollection();
 		$this->properties = new Collections\ArrayCollection();
+		$this->parents = new Collections\ArrayCollection();
 	}
 
 
diff --git a/backend/lib/Router.php b/backend/lib/Router.php
index cfdb731..f6043ad 100644
--- a/backend/lib/Router.php
+++ b/backend/lib/Router.php
@@ -76,7 +76,8 @@ class Router {
 		'group'			=> 'Volkszaehler\Controller\AggregatorController',
 		'token'			=> 'Volkszaehler\Controller\TokenController',
 		'capabilities'	=> 'Volkszaehler\Controller\CapabilitiesController',
-		'data'			=> 'Volkszaehler\Controller\DataController'
+		'data'			=> 'Volkszaehler\Controller\DataController',
+		'entity'		=> 'Volkszaehler\Controller\EntityController'
 	);
 
 	/**
diff --git a/backend/lib/View/JSON.php b/backend/lib/View/JSON.php
index 241cd19..629392b 100644
--- a/backend/lib/View/JSON.php
+++ b/backend/lib/View/JSON.php
@@ -172,12 +172,14 @@ class JSON extends View {
 	protected static function convertAggregator(Model\Aggregator $aggregator) {
 		$jsonAggregator = self::convertEntity($aggregator);
 
-		foreach ($aggregator->getChannels() as $channel) {
-			$jsonAggregator['channels'][] = self::convertEntity($channel);
-		}
+		foreach ($aggregator->getChildren() as $entity) {
 
-		foreach ($aggregator->getChildren() as $subAggregator) {
-			$jsonAggregator['groups'][] = self::convertAggregator($subAggregator);	// recursion
+			if ($entity instanceof Model\Channel) {
+				$jsonAggregator['channels'][] = self::convertEntity($entity);
+			}
+			elseif ($entity instanceof Model\Aggregator) {
+				$jsonAggregator['groups'][] = self::convertAggregator($entity);
+			}
 		}
 
 		return $jsonAggregator;
diff --git a/share/sql/mysql.sql b/share/sql/mysql.sql
index e06bba4..7d167c3 100644
--- a/share/sql/mysql.sql
+++ b/share/sql/mysql.sql
@@ -1,13 +1,12 @@
-CREATE TABLE entities (id SMALLINT AUTO_INCREMENT NOT NULL, uuid VARCHAR(36) NOT NULL, type VARCHAR(255) NOT NULL, class VARCHAR(255) NOT NULL, UNIQUE INDEX entities_uuid_uniq (uuid), PRIMARY KEY(id)) ENGINE = InnoDB;
-CREATE TABLE groups_channel (group_id SMALLINT NOT NULL, channel_id SMALLINT NOT NULL, PRIMARY KEY(group_id, channel_id)) ENGINE = InnoDB;
-CREATE TABLE groups_groups (parent_id SMALLINT NOT NULL, child_id SMALLINT NOT NULL, PRIMARY KEY(parent_id, child_id)) ENGINE = InnoDB;
-CREATE TABLE data (id SMALLINT AUTO_INCREMENT NOT NULL, channel_id SMALLINT DEFAULT NULL, timestamp BIGINT NOT NULL, value NUMERIC(5, 2) NOT NULL, UNIQUE INDEX unique_timestamp (timestamp, channel_id), PRIMARY KEY(id)) ENGINE = InnoDB;
-CREATE TABLE tokens (id SMALLINT AUTO_INCREMENT NOT NULL, entity_id SMALLINT DEFAULT NULL, token VARCHAR(255) NOT NULL, valid BIGINT NOT NULL, UNIQUE INDEX tokens_token_uniq (token), PRIMARY KEY(id)) ENGINE = InnoDB;
-CREATE TABLE properties (id SMALLINT AUTO_INCREMENT NOT NULL, entity_id SMALLINT DEFAULT NULL, `key` VARCHAR(255) NOT NULL, value VARCHAR(255) NOT NULL, UNIQUE INDEX unique_keys (entity_id, `key`), PRIMARY KEY(id)) ENGINE = InnoDB;
-ALTER TABLE groups_channel ADD FOREIGN KEY (group_id) REFERENCES entities(id);
-ALTER TABLE groups_channel ADD FOREIGN KEY (channel_id) REFERENCES entities(id);
-ALTER TABLE groups_groups ADD FOREIGN KEY (parent_id) REFERENCES entities(id);
-ALTER TABLE groups_groups ADD FOREIGN KEY (child_id) REFERENCES entities(id);
-ALTER TABLE data ADD FOREIGN KEY (channel_id) REFERENCES entities(id);
-ALTER TABLE tokens ADD FOREIGN KEY (entity_id) REFERENCES entities(id);
-ALTER TABLE properties ADD FOREIGN KEY (entity_id) REFERENCES entities(id)
+Creating database schema...
+
+
+                                                                                            
+  [PDOException]                                                                            
+  SQLSTATE[42S01]: Base table or view already exists: 1050 Table 'entities' already exists  
+                                                                                            
+
+
+orm:schema-tool:create [--dump-sql] [-h|--help] [-q|--quiet] [-v|--verbose] [-V|--version] [-a|--ansi] [-n|--no-interaction] command
+
+