diff --git a/backend/lib/view/jsonview.php b/backend/lib/view/jsonview.php
index 5290bf8..4d3d78a 100644
--- a/backend/lib/view/jsonview.php
+++ b/backend/lib/view/jsonview.php
@@ -20,83 +20,70 @@
  */
 
 class JsonView extends View {
-	public $data = array();
+	public $jsonData = array();
 
 	public function __construct(HttpRequest $request, HttpResponse $response) {
 		parent::__construct($request, $response);
 
 		$config = Registry::get('config');
 
-		$this->data['source'] = 'volkszaehler.org';
-		$this->data['version'] = VZ_VERSION;
-		$this->data['storage'] = $config['db']['backend'];
-		$this->data['controller'] = $request->get['controller'];
-		$this->data['action'] = $request->get['action'];
+		$this->jsonData['source'] = 'volkszaehler.org';
+		$this->jsonData['version'] = VZ_VERSION;
+		$this->jsonData['storage'] = $config['db']['backend'];
+		$this->jsonData['controller'] = $request->get['controller'];
+		$this->jsonData['action'] = $request->get['action'];
 
 		$this->response->setHeader('Content-type', 'application/json');
 	}
 
 	public function render() {
-		$this->data['time'] = round(microtime(true) - $this->created, 4);
-		echo json_encode($this->data);
+		$this->jsonData['time'] = $this->getTime();
+		echo json_encode($this->jsonData);
 	}
 
-	public function exceptionHandler(Exception $exception) {
-		$this->data['exception'] = array('message' => $exception->getMessage(),
+	protected function addException(Exception $exception) {
+		$this->jsonData['exception'] = array('message' => $exception->getMessage(),
 										'code' => $exception->getCode(),
 										'file' => $exception->getFile(),
 										'line' => $exception->getLine(),
 										'trace' => $exception->getTrace()
 		);
-		$this->data['status'] = 'exception';
-		$this->render();
-		die();
 	}
 
 	public function addChannel(Channel $obj, $data = NULL) {
-			$channel['id'] = (int) $obj->id;
-			$channel['ucid'] = $obj->ucid;
-			$channel['type'] = $obj->type;
-			$channel['unit'] = $obj->unit;
-			$channel['description'] = $obj->description;
-			$channel['resolution'] = (int) $obj->resolution;
-			$channel['costs'] = (float) $obj->cost;
+		$channel['id'] = (int) $obj->id;
+		$channel['ucid'] = $obj->ucid;
+		$channel['type'] = $obj->type;
+		$channel['unit'] = $obj->unit;
+		$channel['description'] = $obj->description;
+		$channel['resolution'] = (int) $obj->resolution;
+		$channel['cost'] = (float) $obj->cost;
 			
-			// TODO check for optional data in second param
-			if (!is_null($data) && is_array($data)) {
-				$channel['data'] = array();
-				foreach ($data as $reading) {
-					$channel['data'][] = array($reading['timestamp'], $reading['value'], $reading['count']);
-				}
+		if (!is_null($data) && is_array($data)) {
+			$channel['data'] = array();
+			foreach ($data as $reading) {
+				$channel['data'][] = array($reading['timestamp'], $reading['value'], $reading['count']);
 			}
+		}
 			
-			$this->data['channels'][] = $channel;
-	}
-			
-	public function addUser(User $obj) {
-			$user['id'] = (int) $obj->id;
-			$user['uuid'] = $obj->uuid;
-			
-			$this->data['users'][] = $user;
+		$this->jsonData['channels'][] = $channel;
 	}
 		
-	public function addGroup(Group $obj) {
-			$group['id'] = (int) $obj->id;
-			$group['ugid'] = $obj->ugid;
-			$group['description'] = $obj->description;
+	public function addUser(User $obj) {
+		$user['id'] = (int) $obj->id;
+		$user['uuid'] = $obj->uuid;
 			
-			// TODO include sub groups?
-			
-			$this->data['groups'][] = $group;
+		$this->jsonData['users'][] = $user;
 	}
+
+	public function addGroup(Group $obj) {
+		$group['id'] = (int) $obj->id;
+		$group['ugid'] = $obj->ugid;
+		$group['description'] = $obj->description;
 			
-	public function add($obj) {
-		if (is_array($obj)) {
-			array_merge($this->data, $obj);	// TODO check array_merge beavior with duplicate keys
-		}
-		else {
-			$this->data[] = $obj;
-		}
+		// TODO include sub groups?
+			
+		$this->jsonData['groups'][] = $group;
 	}
 }
 
diff --git a/backend/lib/view/view.php b/backend/lib/view/view.php
index c96f24d..1db0caa 100644
--- a/backend/lib/view/view.php
+++ b/backend/lib/view/view.php
@@ -25,7 +25,6 @@ interface ViewInterface {
 	public function exceptionHandler(Exception $exception);
 	public function errorHandler($errno, $errstr, $errfile, $errline);
 	
-	public function add($obj);
 	public function addChannel(Channel $obj);
 	public function addUser(User $obj);
 	public function addGroup(Group $obj);
@@ -34,7 +33,7 @@ interface ViewInterface {
 abstract class View implements ViewInterface {
 	public $request;
 	protected $response;
-	protected $created;	// holds timestamp of creation, used later to return time of execution
+	private $created;	// holds timestamp of creation, used later to return time of execution
 	
 	public function __construct(HttpRequest $request, HttpResponse $response) {
 		$this->request = $request;
@@ -50,6 +49,20 @@ abstract class View implements ViewInterface {
 		$this->exceptionHandler(new ErrorException($errstr, 0, $errno, $errfile, $errline));
 	}
 	
+	final public function exceptionHandler(Exception $exception) {
+		$this->addException($exception);
+		
+		//$this->status = STATUS_EXCEPTION;	// TODO add status reporting to API
+		$this->code = 400;					// TODO add Exception => HTTP code mapping
+		
+		$this->render();
+		die();
+	}
+	
+	protected function getTime() {
+		return round(microtime(true) - $this->created, 4);
+	}
+	
 	public function __destruct() {
 		$this->response->send();	// send response
 	}
diff --git a/backend/lib/view/xmlview.php b/backend/lib/view/xmlview.php
index 5792d1d..fa4ef85 100644
--- a/backend/lib/view/xmlview.php
+++ b/backend/lib/view/xmlview.php
@@ -20,77 +20,140 @@
  */
 
 class XmlView extends View {
-	public $doc;
+	private $xmlDoc;
+	private $xml;
+	private $xmlChannels;
+	private $xmlUsers;
+	private $xmlGroups;
 
 	public function __construct(HttpRequest $request, HttpResponse $response) {
 		parent::__construct($request, $response);
 
 		$config = Registry::get('config');
 
-		$this->doc = new DOMDocument('1.0', 'UTF-8');
+		$this->xmlDoc = new DOMDocument('1.0', 'UTF-8');
 
-		$this->source = 'volkszaehler.org';		// TODO create XML
-		$this->version = VZ_VERSION;
-		$this->storage = $config['db']['backend'];
-		$this->controller = $request->get['controller'];
-		$this->action = $request->get['action'];
+		$this->xml = $this->xmlDoc->createElement('volkszaehler');
+		$this->xml->setAttribute('version', VZ_VERSION);
+		$this->xmlChannels = $this->xmlDoc->createElement('channels');
+		$this->xmlUsers = $this->xmlDoc->createElement('users');
+		$this->xmlGroups = $this->xmlDoc->createElement('groups');
 
-		$this->response->headers['Content-type'] = 'application/json';
+		$this->xml->appendChild($this->xmlDoc->createElement('source', 'volkszaehler.org'));
+		$this->xml->appendChild($this->xmlDoc->createElement('storage', $config['db']['backend']));
+		$this->xml->appendChild($this->xmlDoc->createElement('controller', $request->get['controller']));
+		$this->xml->appendChild($this->xmlDoc->createElement('action', $request->get['action']));
+		
+		$this->response->setHeader('Content-type', 'text/xml');
 	}
-	
-	public function getChannel(Channel $channel) {		// TODO improve view interface
-	return array('id' => (int) $channel->id,
-						'ucid' => $channel->ucid,
-						'resolution' => (int) $channel->resolution,
-						'description' => $channel->description,
-						'type' => $channel->type,
-						'costs' => $channel->cost);
+
+	public function addChannel(Channel $obj, $data = NULL) {
+		$xmlChannel = $this->xmlDoc->createElement('channel');
+		$xmlChannel->setAttribute('id', (int) $obj->id);
+		
+		$xmlChannel->appendChild($this->xmlDoc->createElement('ucid', $obj->ucid));
+		$xmlChannel->appendChild($this->xmlDoc->createElement('type', $obj->type));
+		$xmlChannel->appendChild($this->xmlDoc->createElement('unit', $obj->unit));
+		$xmlChannel->appendChild($this->xmlDoc->createElement('description', $obj->description));
+		$xmlChannel->appendChild($this->xmlDoc->createElement('resolution', (int) $obj->resolution));
+		$xmlChannel->appendChild($this->xmlDoc->createElement('cost', (float) $obj->cost));
+		
+		if (!is_null($data) && is_array($data)) {
+			$xmlData = $this->xmlDoc->createElement('data');
+			
+			foreach ($data as $reading) {
+				$xmlReading = $this->xmlDoc->createElement('reading');
+				
+				$xmlReading->setAttribute('timestamp', $reading['timestamp']);	// hardcoded data fields for performance optimization
+				$xmlReading->setAttribute('value', $reading['value']);
+				$xmlReading->setAttribute('count', $reading['count']);
+				
+				$xmlData->appendChild($xmlReading);
+			}
+			
+			$xmlChannel->appendChild($xmlData);
+		}
+			
+		$this->xmlChannels->appendChild($xmlChannel);
+	}
+		
+	public function addUser(User $obj) {
+		$xmlUser = $this->xmlDoc->createElement('user');
+		$xmlUser->setAttribute('id', (int) $obj->id);
+		$xmlUser->appendChild($this->xmlDoc->createElement('uuid', $obj->uuid));
+			
+		$this->xmlUsers->appendChild($xmlUser);
+	}
+
+	public function addGroup(Group $obj) {
+		$xmlGroup = $this->xmlDoc->createElement('group');
+		$xmlGroup->setAttribute('id', (int) $obj->id);
+		$xmlGroup->appendChild($this->xmlDoc->createElement('ugid', $obj->uuid));
+		$xmlGroup->appendChild($this->xmlDoc->createElement('description', $obj->description));
+			
+		// TODO include sub groups?
+			
+		$this->xmlGroups->appendChild($xmlGroup);
 	}
 
 	public function render() {
-		$this->time = round(microtime(true) - $this->created, 4);
-		echo json_encode($this->data);
+		$this->xml->appendChild($this->xmlDoc->createElement('time', $this->getTime()));
+		
+		// channels
+		if ($this->xmlChannels->hasChildNodes()) {
+			$this->xml->appendChild($this->xmlChannels);
+		}
+		
+		// users
+		if ($this->xmlUsers->hasChildNodes()) {
+			$this->xml->appendChild($this->xmlUsers);
+		}
+		
+		// groups
+		if ($this->xmlGroups->hasChildNodes()) {
+			$this->xml->appendChild($this->xmlGroups);
+		}
+		
+		$this->xmlDoc->appendChild($this->xml);
+		echo $this->xmlDoc->saveXML();
 	}
 
-	public function exceptionHandler(Exception $exception) {
-		$xmlException = $this->doc->createElement('exception');
-
+	protected function addException(Exception $exception) {
+		$xmlException = $this->xmlDoc->createElement('exception');
 		$xmlException->setAttribute('code', $exception->getCode());
+		$xmlException->appendChild($this->xmlDoc->createElement('message', $exception->getMessage()));
+		$xmlException->appendChild($this->xmlDoc->createElement('line', $exception->getLine()));
+		$xmlException->appendChild($this->xmlDoc->createElement('file', $exception->getFile()));
+		$xmlException->appendChild($this->fromTrace($exception->getTrace()));
 
-		$xmlException->appendChild($this->doc->createElement('message', $exception->getMessage()));
-		$xmlException->appendChild($this->doc->createElement('line', $exception->getLine()));
-		$xmlException->appendChild($this->doc->createElement('file', $exception->getFile()));
-
-		$xmlException->appendChild($this->backtrace($exception->getTrace()));
-
-		$this->render();
-		die();
+		$this->xml->appendChild($xmlException);
 	}
 
-	function backtrace($traces) {
-		$xmlTraces = $this->doc->createElement('backtrace');
+	private function fromTrace($traces) {
+		$xmlTraces = $this->xmlDoc->createElement('backtrace');
 
 		foreach ($traces as $step => $trace) {
-			$xmlTrace = $this->doc->createElement('trace');
+			$xmlTrace = $this->xmlDoc->createElement('trace');
 			$xmlTraces->appendChild($xmlTrace);
 			$xmlTrace->setAttribute('step', $step);
 
 			foreach ($trace as $key => $value) {
 				switch ($key) {
+					case 'args':
+						$xmlArgs = $this->xmlDoc->createElement($key);
+						$xmlTrace->appendChild($xmlArgs);
+						foreach ($value as $arg) {
+							$xmlArgs->appendChild($this->xmlDoc->createElement('arg', print_r($value, true))); // TODO check $value content
+						}
+						break;
+							
+					case 'type':
 					case 'function':
 					case 'line':
 					case 'file':
 					case 'class':
-					case 'type':
-						$xmlTrace->appendChild($this->doc->createElement($key, $value));
-						break;
-					case 'args':
-						$xmlArgs = $doc->createElement($key);
-						$xmlTrace->appendChild($xmlArgs);
-						foreach ($value as $arg) {
-							$xmlArgs->appendChild($this->doc->createElement('arg', $value));
-						}
-						break;
+					default:
+						$xmlTrace->appendChild($this->xmlDoc->createElement($key, $value));
 				}
 			}
 		}