diff --git a/src/AbstractConnection.php b/src/AbstractConnection.php
index 1354770..3008bf3 100644
--- a/src/AbstractConnection.php
+++ b/src/AbstractConnection.php
@@ -56,7 +56,7 @@ abstract class AbstractConnection extends Component implements ConnectionInterfa
     protected $_handler;
 
     /**
-     * @var QueryBuilder the query builder for this connection
+     * @var AbstractQueryBuilder the query builder for this connection
      */
     protected $_builder;
 
@@ -77,6 +77,10 @@ abstract class AbstractConnection extends Component implements ConnectionInterfa
      */
     protected $_errorChecker;
 
+    /**
+     * @param null $dbname
+     * @return ConnectionInterface|AbstractConnection
+     */
     public static function getDb($dbname = null)
     {
         return $dbname ? Yii::$app->get($dbname) : Yii::$container->get(ConnectionInterface::class);
@@ -144,7 +148,7 @@ public function createCommand(array $config = [])
     }
 
     /**
-     * @return QueryBuilder the query builder for this connection
+     * @return AbstractQueryBuilder the query builder for this connection
      */
     public function getQueryBuilder()
     {
@@ -220,45 +224,30 @@ public function setErrorChecker($checker)
     }
 
     /**
-     * Checks response with checkError method and raises exception if error.
+     * Checks response method and raises exception if error found.
      * @param ResponseInterface $response response data from API
-     * @throws ErrorResponseException
-     * @return mixed response data
+     * @throws ResponseErrorException when response is invalid
      */
     public function checkResponse(ResponseInterface $response)
-    {
-        $error = $this->checkError($response);
-        if ($error) {
-            throw new ErrorResponseException($error, [
-                'request' => $response->getRequest()->getParts(),
-                'response' => $response->getData(),
-            ]);
-        }
-    }
-
-    /**
-     * Checks response with errorChecker callback and returns error text if error.
-     * @param ResponseInterface $response
-     * @return string|false error text or false
-     */
-    public function checkError(ResponseInterface $response)
     {
         if (isset($this->_errorChecker)) {
-            return call_user_func($this->_errorChecker, $response);
+            $error = call_user_func($this->_errorChecker, $response);
         } else {
-            return $this->isError($response);
+            $error = $this->getResponseError($response);
+        }
+
+        if ($error) {
+            throw new ResponseErrorException($error, $response);
         }
     }
 
     /**
-     * Default error checker. TODO check something in response?
+     * Method checks whether the response is an error
+     *
      * @param ResponseInterface $response
-     * @return bool
+     * @return false|string the error text or boolean `false`, when the response is not an error
      */
-    public function isError(ResponseInterface $response)
-    {
-        return false;
-    }
+    abstract public function getResponseError(ResponseInterface $response);
 
     /**
      * Return API base uri.
diff --git a/src/AbstractQueryBuilder.php b/src/AbstractQueryBuilder.php
index 0b050c8..0870a49 100644
--- a/src/AbstractQueryBuilder.php
+++ b/src/AbstractQueryBuilder.php
@@ -81,7 +81,7 @@ abstract public function buildBody(Query $query);
      * @param string $table
      * @param array $columns
      * @param array $options
-     * @return Request
+     * @return AbstractRequest
      */
     public function insert($table, $columns, array $options = [])
     {
@@ -93,7 +93,7 @@ public function insert($table, $columns, array $options = [])
      * @param string $table
      * @param array $columns
      * @param array $options
-     * @return Request
+     * @return AbstractRequest
      */
     public function update($table, $columns, $condition = [], array $options = [])
     {
diff --git a/src/AbstractRequest.php b/src/AbstractRequest.php
index 3afe2f4..a2c6347 100644
--- a/src/AbstractRequest.php
+++ b/src/AbstractRequest.php
@@ -258,6 +258,9 @@ protected function prepareUserAgent()
         return $this->getDb()->getUserAgent();
     }
 
+    /**
+     * @return AbstractConnection|ConnectionInterface
+     */
     public function getDb()
     {
         return isset($this->builder) ? $this->builder->db : AbstractConnection::getDb($this->dbname);
diff --git a/src/AbstractResponse.php b/src/AbstractResponse.php
index cdcacce..aa71a6b 100644
--- a/src/AbstractResponse.php
+++ b/src/AbstractResponse.php
@@ -20,10 +20,15 @@ abstract class AbstractResponse implements ResponseInterface
     protected $request;
 
     /**
-     * @var mixed response data
+     * @var string response data. The property contains RAW response data
+     * @see decodeData()
+     * @see isDecoded
      */
     protected $data;
 
+    /**
+     * @var bool whether response is already decoded
+     */
     protected $isDecoded = false;
 
     public function getRequest()
@@ -44,20 +49,42 @@ public function getData()
     public function decodeData()
     {
         $data = $this->getRawData();
-        if (!$this->isRaw() && $this->isJson()) {
-            $data = Json::decode($data);
+
+        if ($this->isRaw()) {
+            return $data;
         }
 
+        if ($this->isJson()) {
+            return Json::decode($data);
+        }
+
+        // TODO: implement decoding for XML and other types
+
+        // throw new ResponseDecodingException('Failed to detect response data type', $this);
+        // TODO: throw exception instead of returning
         return $data;
     }
 
+    /**
+     * Method returns RAW request data
+     *
+     * @return string
+     */
     abstract public function getRawData();
 
+    /**
+     * Whether the request is RAW and should not be decoded
+     * @return bool
+     */
     public function isRaw()
     {
         return $this->request->isRaw();
     }
 
+    /**
+     * Method checks whether response is a JSON response
+     * @return bool
+     */
     public function isJson()
     {
         return !empty(preg_grep('|application/json|i', $this->getHeader('Content-Type')));
diff --git a/src/ActiveQuery.php b/src/ActiveQuery.php
index fbc5577..ee1ad58 100644
--- a/src/ActiveQuery.php
+++ b/src/ActiveQuery.php
@@ -10,6 +10,7 @@
 
 namespace hiqdev\hiart;
 
+use hiqdev\hiart\rest\QueryBuilder;
 use yii\db\ActiveQueryInterface;
 use yii\db\ActiveQueryTrait;
 use yii\db\ActiveRelationTrait;
diff --git a/src/ActiveRecord.php b/src/ActiveRecord.php
index 3f7e110..f596a9f 100644
--- a/src/ActiveRecord.php
+++ b/src/ActiveRecord.php
@@ -25,7 +25,7 @@ class ActiveRecord extends BaseActiveRecord
      * By default, the "hiart" application component is used as the database connection.
      * You may override this method if you want to use a different database connection.
      *
-     * @return Connection the database connection used by this AR class
+     * @return AbstractConnection the database connection used by this AR class
      */
     public static function getDb()
     {
diff --git a/src/Collection.php b/src/Collection.php
index cde5f0a..e8e1974 100644
--- a/src/Collection.php
+++ b/src/Collection.php
@@ -334,7 +334,7 @@ public function insert($runValidation = true, $attributes = null, array $options
             $model->afterSave(true, $changedAttributes);
         }
 
-        $this->afterSave(true);
+        $this->afterSave();
 
         return true;
     }
diff --git a/src/Command.php b/src/Command.php
index 4303da1..5247148 100644
--- a/src/Command.php
+++ b/src/Command.php
@@ -18,7 +18,7 @@
 class Command extends \yii\base\Component
 {
     /**
-     * @var Connection
+     * @var AbstractConnection
      */
     public $db;
 
diff --git a/src/Exception.php b/src/Exception.php
index a78f839..9e48ae8 100644
--- a/src/Exception.php
+++ b/src/Exception.php
@@ -10,6 +10,9 @@
 
 namespace hiqdev\hiart;
 
+/**
+ * Class Exception represent general exception occurred in HiArt
+ */
 class Exception extends \yii\db\Exception
 {
     /**
diff --git a/src/QueryBuilderInterface.php b/src/QueryBuilderInterface.php
index 47b5ba2..3682e4d 100644
--- a/src/QueryBuilderInterface.php
+++ b/src/QueryBuilderInterface.php
@@ -37,4 +37,6 @@ public function buildQueryParams(Query $query);
     public function buildFormParams(Query $query);
 
     public function buildBody(Query $query);
+
+    public function prepare(Query $query);
 }
diff --git a/src/RequestErrorException.php b/src/RequestErrorException.php
index 0880525..3d9fbca 100644
--- a/src/RequestErrorException.php
+++ b/src/RequestErrorException.php
@@ -11,12 +11,37 @@
 namespace hiqdev\hiart;
 
 /**
- * Request error exception.
- *
- * For exceptions during request sending.
+ * Class RequestErrorException represents an error occurred during the request sending
  */
 class RequestErrorException extends Exception
 {
+    /**
+     * @var RequestInterface
+     */
+    protected $request;
+
+    /**
+     * RequestErrorException constructor.
+     *
+     * @param string $message
+     * @param RequestInterface $request
+     * @param array $errorInfo
+     * @param int $code
+     * @param \Exception|null $previous
+     */
+    public function __construct(
+        $message,
+        RequestInterface $request,
+        array $errorInfo = [],
+        $code = 0,
+        \Exception $previous = null
+    ) {
+        $this->request = $request;
+        $errorInfo = array_merge($this->getDetailsArray(), $errorInfo);
+
+        parent::__construct($message, $errorInfo, $code, $previous);
+    }
+
     /**
      * @return RequestInterface
      */
@@ -24,4 +49,18 @@ public function getRequest()
     {
         return $this->errorInfo['request'];
     }
+
+    /**
+     * @return array
+     */
+    protected function getDetailsArray()
+    {
+        $request = $this->getRequest();
+
+        return [
+            'method' => $request->getMethod(),
+            'uri' => $request->getFullUri(),
+            'body' => $request->getBody(),
+        ];
+    }
 }
diff --git a/src/RequestInterface.php b/src/RequestInterface.php
index 1c7c1af..4e18563 100644
--- a/src/RequestInterface.php
+++ b/src/RequestInterface.php
@@ -10,7 +10,30 @@
 
 namespace hiqdev\hiart;
 
+use hiqdev\hiart\curl\Response;
+
 interface RequestInterface extends \Serializable
 {
+    /**
+     * @param array $options
+     * @return Response
+     * @throws RequestErrorException
+     */
     public function send($options = []);
+
+    /**
+     * @return string
+     */
+    public function getBody();
+
+    /**
+     * @return string
+     */
+    public function getFullUri();
+
+    /**
+     * Method returns the Request method in the uppercase, e.g. GET, POST, DELETE
+     * @return string
+     */
+    public function getMethod();
 }
diff --git a/src/ResponseDecodingException.php b/src/ResponseDecodingException.php
new file mode 100644
index 0000000..b91cf47
--- /dev/null
+++ b/src/ResponseDecodingException.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace hiqdev\hiart;
+
+class ResponseDecodingException extends ResponseErrorException
+{
+    /**
+     * @return mixed
+     */
+    public function getName()
+    {
+        return 'Failed to decode the response';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function getDetailsArray()
+    {
+        $request = $this->getRequest();
+        $response = $this->getResponse();
+
+        return [
+            'statusCode' => $response->getStatusCode(),
+            'responseData' => $response->getRawData(),
+            'request' => [
+                'method' => $request->getMethod(),
+                'uri' => $request->getFullUri(),
+                'body' => $request->getBody(),
+            ],
+        ];
+    }
+}
diff --git a/src/ResponseErrorException.php b/src/ResponseErrorException.php
index 97ea331..b6c21a8 100644
--- a/src/ResponseErrorException.php
+++ b/src/ResponseErrorException.php
@@ -11,17 +11,77 @@
 namespace hiqdev\hiart;
 
 /**
- * Response error exception.
- *
- * For exceptions during response processing.
+ * Class ResponseErrorException represent exception occurred during the response processing.
  */
 class ResponseErrorException extends Exception
 {
+    /**
+     * @var ResponseInterface
+     */
+    protected $response;
+
+    /**
+     * ResponseErrorException constructor
+     *
+     * @param string $message the error message
+     * @param ResponseInterface $response
+     * @param array $errorInfo
+     * @param int $code
+     * @param \Exception|null $previous
+     */
+    public function __construct(
+        $message,
+        ResponseInterface $response,
+        array $errorInfo = [],
+        $code = 0,
+        \Exception $previous = null
+    ) {
+        $this->response = $response;
+        $errorInfo = array_merge($this->getDetailsArray(), $errorInfo);
+
+        parent::__construct($message, $errorInfo, $code, $previous);
+    }
+
     /**
      * @return ResponseInterface
      */
     public function getResponse()
     {
-        return $this->errorInfo['response'];
+        return $this->response;
+    }
+
+    /**
+     * @return RequestInterface
+     */
+    public function getRequest()
+    {
+        return $this->response->getRequest();
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getResponseData()
+    {
+        return $this->getResponse()->getData();
+    }
+
+    /**
+     * @return array
+     */
+    protected function getDetailsArray()
+    {
+        $request = $this->getRequest();
+        $response = $this->getResponse();
+
+        return [
+            'statusCode' => $response->getStatusCode(),
+            'responseData' => $response->getData(),
+            'request' => [
+                'method' => $request->getMethod(),
+                'uri' => $request->getFullUri(),
+                'body' => $request->getBody(),
+            ],
+        ];
     }
 }
diff --git a/src/ResponseInterface.php b/src/ResponseInterface.php
index 72cd5a4..6be6c78 100644
--- a/src/ResponseInterface.php
+++ b/src/ResponseInterface.php
@@ -12,6 +12,9 @@
 
 interface ResponseInterface
 {
+    /**
+     * @return RequestInterface
+     */
     public function getRequest();
 
     public function getData();
@@ -19,4 +22,8 @@ public function getData();
     public function getRawData();
 
     public function getHeader($name);
+
+    public function getStatusCode();
+
+    public function getReasonPhrase();
 }
diff --git a/src/curl/Request.php b/src/curl/Request.php
index 404ea6c..6dcab75 100644
--- a/src/curl/Request.php
+++ b/src/curl/Request.php
@@ -13,15 +13,12 @@
 use hiqdev\hiart\AbstractRequest;
 
 /**
- * cURL request implementation.
- *
- * @author Andrii Vasyliev <sol@hiqdev.com>
+ * Class Request represents request using cURL library
  */
 class Request extends AbstractRequest
 {
-    protected $workerClass = RequestWorker::class;
-
-    protected function createWorker()
+    public function send($options = [])
     {
+
     }
 }
diff --git a/src/curl/Response.php b/src/curl/Response.php
index b4e6e14..391713e 100644
--- a/src/curl/Response.php
+++ b/src/curl/Response.php
@@ -19,8 +19,23 @@
  */
 class Response extends AbstractResponse
 {
-    /**
-     * @var ResponseWorker
-     */
-    protected $worker;
+    public function getRawData()
+    {
+
+    }
+
+    public function getHeader($name)
+    {
+
+    }
+
+    public function getStatusCode()
+    {
+
+    }
+
+    public function getReasonPhrase()
+    {
+
+    }
 }
diff --git a/src/rest/Connection.php b/src/rest/Connection.php
index 9a032e6..bbc9dcc 100644
--- a/src/rest/Connection.php
+++ b/src/rest/Connection.php
@@ -17,16 +17,20 @@ class Connection extends \hiqdev\hiart\AbstractConnection
 {
     public $queryBuilderClass = QueryBuilder::class;
 
-    public function checkResponse(ResponseInterface $response)
+    /**
+     * Method checks whether the response is an error
+     *
+     * @param ResponseInterface $response
+     * @return false|string the error text or boolean `false`, when the response is not an error
+     */
+    public function getResponseError(ResponseInterface $response)
     {
         $code = $response->getStatusCode();
         if ($code >= 200 && $code < 300) {
-            return;
+            return false;
         }
 
-        throw new ResponseErrorException($response->getReasonPhrase(), [
-            'request' => $response->getRequest()->getParts(),
-            'response' => $response->getData(),
-        ], $code);
+        return $response->getReasonPhrase();
+
     }
 }