diff --git a/framework/caching/Cache.php b/framework/caching/Cache.php
index 20631a7..a35785c 100644
--- a/framework/caching/Cache.php
+++ b/framework/caching/Cache.php
@@ -9,8 +9,7 @@
 
 namespace yii\caching;
 
-use yii\base\ApplicationComponent;
-use yii\base\InvalidCallException;
+use yii\base\Component;
 
 /**
  * Cache is the base class for cache classes supporting different cache storage implementation.
@@ -21,13 +20,16 @@ use yii\base\InvalidCallException;
  * can also be specified when calling [[set()]]. If the data item expires or the dependency
  * changes at the time of calling [[get()]], the cache will return no data.
  *
- * Derived classes should implement the following methods:
+ * A typical usage pattern of cache is like the following:
  *
- * - [[getValue]]: retrieve the value with a key (if any) from cache
- * - [[setValue]]: store the value with a key into cache
- * - [[addValue]]: store the value only if the cache does not have this key before
- * - [[deleteValue]]: delete the value with the specified key from cache
- * - [[flushValues]]: delete all values from cache
+ * ~~~
+ * $key = 'demo';
+ * $data = $cache->get($key);
+ * if ($data === false) {
+ *     // ...generate $data here...
+ *     $cache->set($key, $data, $expire, $dependency);
+ * }
+ * ~~~
  *
  * Because Cache implements the ArrayAccess interface, it can be used like an array. For example,
  *
@@ -36,10 +38,19 @@ use yii\base\InvalidCallException;
  * echo $cache['foo'];
  * ~~~
  *
+ * Derived classes should implement the following methods:
+ *
+ * - [[getValue()]]: retrieve the value with a key (if any) from cache
+ * - [[setValue()]]: store the value with a key into cache
+ * - [[addValue()]]: store the value only if the cache does not have this key before
+ * - [[deleteValue()]]: delete the value with the specified key from cache
+ * - [[flushValues()]]: delete all values from cache
+ *
+ *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
-abstract class Cache extends ApplicationComponent implements \ArrayAccess
+abstract class Cache extends Component implements \ArrayAccess
 {
 	/**
 	 * @var string a string prefixed to every cache key so that it is unique. Defaults to null, meaning using
@@ -59,64 +70,45 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 	 */
 	public $serializer;
 
-	/**
-	 * Initializes the application component.
-	 * This method overrides the parent implementation by setting default cache key prefix.
-	 */
-	public function init()
-	{
-		parent::init();
-		if ($this->keyPrefix === null) {
-			$this->keyPrefix = \Yii::$application->id;
-		}
-	}
 
 	/**
-	 * Generates a cache key from one or multiple parameters.
-	 * The cache key generated is safe to be used to access cache via methods such as [[get()]], [[set()]].
-	 * For example:
+	 * Builds a normalized cache key from one or multiple parameters.
+	 *
+	 * The generated key contains letters and digits only, and its length is no more than 32.
+	 * 
+	 * If only one parameter is given and it is already a normalized key, then
+	 * it will be returned back without change. Otherwise, a normalized key
+	 * is generated by serializing all given parameters and applying MD5 hashing. 
+	 * 
+	 * The following example builds a cache key using three parameters:
 	 *
 	 * ~~~
 	 * $key = $cache->buildKey($className, $method, $id);
 	 * ~~~
 	 *
-	 * @param string $id the
-	 * @return string the cache key
-	 * @throws InvalidCallException if the method receives no parameter
+	 * @param string $key the first parameter
+	 * @return string the generated cache key
 	 */
-	public function generateKey($id)
+	public function buildKey($key)
 	{
-		$n = func_num_args();
-		if ($n === 1 && is_string($id) && ctype_alnum($id) && strlen($id) <= 32) {
-			return $this->keyPrefix . $id;
-		} elseif ($n < 1) {
-			throw new InvalidCallException(__METHOD__ . ' requires at least one parameter.');
+		if (func_num_args() === 1 && ctype_alnum($key) && strlen($key) <= 32) {
+			return (string)$key;
 		} else {
 			$params = func_get_args();
-			return $this->keyPrefix . md5(serialize($params));
+			return md5(serialize($params));
 		}
 	}
 
 	/**
-	 * Generates a normalized key from a given key.
-	 * The normalized key is obtained by hashing the given key via MD5 and then prefixing it with [[keyPrefix]].
-	 * @param string $key a key identifying a value to be cached
-	 * @return string a key generated from the provided key which ensures the uniqueness across applications
-	 */
-	protected function generateKey($key)
-	{
-		return $this->keyPrefix . md5($key);
-	}
-
-	/**
 	 * Retrieves a value from cache with a specified key.
-	 * @param string $id a key identifying the cached value
+	 * @param string $key a key identifying the cached value
 	 * @return mixed the value stored in cache, false if the value is not in the cache, expired,
 	 * or the dependency associated with the cached data has changed.
 	 */
-	public function get($id)
+	public function get($key)
 	{
-		$value = $this->getValue($this->generateKey($id));
+		$key = $this->keyPrefix . $this->buildKey($key);
+		$value = $this->getValue($key);
 		if ($value === false || $this->serializer === false) {
 			return $value;
 		} elseif ($this->serializer === null) {
@@ -124,7 +116,7 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 		} else {
 			$value = call_user_func($this->serializer[1], $value);
 		}
-		if (is_array($value) && ($value[1] instanceof Dependency) || !$value[1]->getHasChanged()) {
+		if (is_array($value) && !($value[1] instanceof Dependency && $value[1]->getHasChanged())) {
 			return $value[0];
 		} else {
 			return false;
@@ -136,30 +128,30 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 	 * Some caches (such as memcache, apc) allow retrieving multiple cached values at the same time,
 	 * which may improve the performance. In case a cache does not support this feature natively,
 	 * this method will try to simulate it.
-	 * @param array $ids list of keys identifying the cached values
+	 * @param array $keys list of keys identifying the cached values
 	 * @return array list of cached values corresponding to the specified keys. The array
 	 * is returned in terms of (key,value) pairs.
 	 * If a value is not cached or expired, the corresponding array value will be false.
 	 */
-	public function mget($ids)
+	public function mget($keys)
 	{
-		$uids = array();
-		foreach ($ids as $id) {
-			$uids[$id] = $this->generateKey($id);
+		$keyMap = array();
+		foreach ($keys as $key) {
+			$keyMap[$key] = $this->keyPrefix . $this->buildKey($key);
 		}
-		$values = $this->getValues($uids);
+		$values = $this->getValues(array_values($keyMap));
 		$results = array();
-		if ($this->serializer === false) {
-			foreach ($uids as $id => $uid) {
-				$results[$id] = isset($values[$uid]) ? $values[$uid] : false;
-			}
-		} else {
-			foreach ($uids as $id => $uid) {
-				$results[$id] = false;
-				if (isset($values[$uid])) {
-					$value = $this->serializer === null ? unserialize($values[$uid]) : call_user_func($this->serializer[1], $values[$uid]);
-					if (is_array($value) && (!($value[1] instanceof Dependency) || !$value[1]->getHasChanged())) {
-						$results[$id] = $value[0];
+		foreach ($keyMap as $key => $newKey) {
+			$results[$key] = false;
+			if (isset($values[$newKey])) {
+				if ($this->serializer === false) {
+					$results[$key] = $values[$newKey];
+				} else {
+					$value = $this->serializer === null ? unserialize($values[$newKey])
+							: call_user_func($this->serializer[1], $values[$newKey]);
+
+					if (is_array($value) && !($value[1] instanceof Dependency && $value[1]->getHasChanged())) {
+						$results[$key] = $value[0];
 					}
 				}
 			}
@@ -172,14 +164,15 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 	 * If the cache already contains such a key, the existing value and
 	 * expiration time will be replaced with the new ones, respectively.
 	 *
-	 * @param string $id the key identifying the value to be cached
+	 * @param string $key the key identifying the value to be cached
 	 * @param mixed $value the value to be cached
 	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @param Dependency $dependency dependency of the cached item. If the dependency changes,
 	 * the corresponding value in the cache will be invalidated when it is fetched via [[get()]].
+	 * This parameter is ignored if [[serializer]] is false.
 	 * @return boolean whether the value is successfully stored into cache
 	 */
-	public function set($id, $value, $expire = 0, $dependency = null)
+	public function set($key, $value, $expire = 0, $dependency = null)
 	{
 		if ($dependency !== null && $this->serializer !== false) {
 			$dependency->evaluateDependency();
@@ -189,20 +182,22 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 		} elseif ($this->serializer !== false) {
 			$value = call_user_func($this->serializer[0], array($value, $dependency));
 		}
-		return $this->setValue($this->generateKey($id), $value, $expire);
+		$key = $this->keyPrefix . $this->buildKey($key);
+		return $this->setValue($key, $value, $expire);
 	}
 
 	/**
 	 * Stores a value identified by a key into cache if the cache does not contain this key.
 	 * Nothing will be done if the cache already contains the key.
-	 * @param string $id the key identifying the value to be cached
+	 * @param string $key the key identifying the value to be cached
 	 * @param mixed $value the value to be cached
 	 * @param integer $expire the number of seconds in which the cached value will expire. 0 means never expire.
 	 * @param Dependency $dependency dependency of the cached item. If the dependency changes,
 	 * the corresponding value in the cache will be invalidated when it is fetched via [[get()]].
+	 * This parameter is ignored if [[serializer]] is false.
 	 * @return boolean whether the value is successfully stored into cache
 	 */
-	public function add($id, $value, $expire = 0, $dependency = null)
+	public function add($key, $value, $expire = 0, $dependency = null)
 	{
 		if ($dependency !== null && $this->serializer !== false) {
 			$dependency->evaluateDependency();
@@ -212,17 +207,19 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 		} elseif ($this->serializer !== false) {
 			$value = call_user_func($this->serializer[0], array($value, $dependency));
 		}
-		return $this->addValue($this->generateKey($id), $value, $expire);
+		$key = $this->keyPrefix . $this->buildKey($key);
+		return $this->addValue($key, $value, $expire);
 	}
 
 	/**
 	 * Deletes a value with the specified key from cache
-	 * @param string $id the key of the value to be deleted
+	 * @param string $key the key of the value to be deleted
 	 * @return boolean if no error happens during deletion
 	 */
-	public function delete($id)
+	public function delete($key)
 	{
-		return $this->deleteValue($this->generateKey($id));
+		$key = $this->keyPrefix . $this->buildKey($key);
+		return $this->deleteValue($key);
 	}
 
 	/**
@@ -301,23 +298,23 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 	/**
 	 * Returns whether there is a cache entry with a specified key.
 	 * This method is required by the interface ArrayAccess.
-	 * @param string $id a key identifying the cached value
+	 * @param string $key a key identifying the cached value
 	 * @return boolean
 	 */
-	public function offsetExists($id)
+	public function offsetExists($key)
 	{
-		return $this->get($id) !== false;
+		return $this->get($key) !== false;
 	}
 
 	/**
 	 * Retrieves the value from cache with a specified key.
 	 * This method is required by the interface ArrayAccess.
-	 * @param string $id a key identifying the cached value
+	 * @param string $key a key identifying the cached value
 	 * @return mixed the value stored in cache, false if the value is not in the cache or expired.
 	 */
-	public function offsetGet($id)
+	public function offsetGet($key)
 	{
-		return $this->get($id);
+		return $this->get($key);
 	}
 
 	/**
@@ -325,21 +322,21 @@ abstract class Cache extends ApplicationComponent implements \ArrayAccess
 	 * If the cache already contains such a key, the existing value will be
 	 * replaced with the new ones. To add expiration and dependencies, use the [[set()]] method.
 	 * This method is required by the interface ArrayAccess.
-	 * @param string $id the key identifying the value to be cached
+	 * @param string $key the key identifying the value to be cached
 	 * @param mixed $value the value to be cached
 	 */
-	public function offsetSet($id, $value)
+	public function offsetSet($key, $value)
 	{
-		$this->set($id, $value);
+		$this->set($key, $value);
 	}
 
 	/**
 	 * Deletes the value with the specified key from cache
 	 * This method is required by the interface ArrayAccess.
-	 * @param string $id the key of the value to be deleted
+	 * @param string $key the key of the value to be deleted
 	 */
-	public function offsetUnset($id)
+	public function offsetUnset($key)
 	{
-		$this->delete($id);
+		$this->delete($key);
 	}
 }
\ No newline at end of file
diff --git a/framework/caching/ChainedDependency.php b/framework/caching/ChainedDependency.php
index e885308..570715d 100644
--- a/framework/caching/ChainedDependency.php
+++ b/framework/caching/ChainedDependency.php
@@ -81,9 +81,9 @@ class ChainedDependency extends Dependency
 	 */
 	public function getHasChanged()
 	{
-		foreach ($this->dependencies as $dependency) {
+		foreach ($this->dependencies as $i => $dependency) {
 			if (!$dependency instanceof Dependency) {
-				$dependency = \Yii::createObject($dependency);
+				$this->dependencies[$i] = $dependency = \Yii::createObject($dependency);
 			}
 			if ($this->dependOnAll && $dependency->getHasChanged()) {
 				return true;
diff --git a/framework/caching/DbCache.php b/framework/caching/DbCache.php
index 23d8b1f..4b84bfd 100644
--- a/framework/caching/DbCache.php
+++ b/framework/caching/DbCache.php
@@ -9,7 +9,7 @@
 
 namespace yii\caching;
 
-use yii\base\Exception;
+use yii\base\InvalidConfigException;
 use yii\db\Connection;
 use yii\db\Query;
 
@@ -21,11 +21,11 @@ use yii\db\Query;
  *
  * ~~~
  * CREATE TABLE tbl_cache (
- *   id char(128) NOT NULL,
- *   expire int(11) DEFAULT NULL,
- *   data LONGBLOB,
- *   PRIMARY KEY (id),
- *   KEY expire (expire)
+ *     id char(128) NOT NULL,
+ *     expire int(11) DEFAULT NULL,
+ *     data LONGBLOB,
+ *     PRIMARY KEY (id),
+ *     KEY expire (expire)
  * );
  * ~~~
  *
@@ -57,7 +57,7 @@ class DbCache extends Cache
 	public $cacheTableName = 'tbl_cache';
 	/**
 	 * @var integer the probability (parts per million) that garbage collection (GC) should be performed
-	 * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
+	 * when storing a piece of data in the cache. Defaults to 10, meaning 0.001% chance.
 	 * This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.
 	 **/
 	public $gcProbability = 100;
@@ -69,7 +69,7 @@ class DbCache extends Cache
 	/**
 	 * Returns the DB connection instance used for caching purpose.
 	 * @return Connection the DB connection instance
-	 * @throws Exception if [[connectionID]] does not point to a valid application component.
+	 * @throws InvalidConfigException if [[connectionID]] does not point to a valid application component.
 	 */
 	public function getDb()
 	{
@@ -78,7 +78,7 @@ class DbCache extends Cache
 			if ($db instanceof Connection) {
 				$this->_db = $db;
 			} else {
-				throw new Exception("DbCache.connectionID must refer to the ID of a DB connection application component.");
+				throw new InvalidConfigException("DbCache::connectionID must refer to the ID of a DB application component.");
 			}
 		}
 		return $this->_db;
@@ -163,13 +163,13 @@ class DbCache extends Cache
 	 */
 	protected function setValue($key, $value, $expire)
 	{
-		$query = new Query;
-		$command = $query->update($this->cacheTableName, array(
+		$command = $this->getDb()->createCommand();
+		$command->update($this->cacheTableName, array(
 			'expire' => $expire > 0 ? $expire + time() : 0,
 			'data' => array($value, \PDO::PARAM_LOB),
 		), array(
 			'id' => $key,
-		))->createCommand($this->getDb());
+		));;
 
 		if ($command->execute()) {
 			$this->gc();
@@ -198,16 +198,16 @@ class DbCache extends Cache
 			$expire = 0;
 		}
 
-		$query = new Query;
-		$command = $query->insert($this->cacheTableName, array(
+		$command = $this->getDb()->createCommand();
+		$command->insert($this->cacheTableName, array(
 			'id' => $key,
 			'expire' => $expire,
 			'data' => array($value, \PDO::PARAM_LOB),
-		))->createCommand($this->getDb());
+		));
 		try {
 			$command->execute();
 			return true;
-		} catch (Exception $e) {
+		} catch (\Exception $e) {
 			return false;
 		}
 	}
@@ -220,10 +220,8 @@ class DbCache extends Cache
 	 */
 	protected function deleteValue($key)
 	{
-		$query = new Query;
-		$query->delete($this->cacheTableName, array('id' => $key))
-			->createCommand($this->getDb())
-			->execute();
+		$command = $this->getDb()->createCommand();
+		$command->delete($this->cacheTableName, array('id' => $key))->execute();
 		return true;
 	}
 
@@ -235,10 +233,8 @@ class DbCache extends Cache
 	public function gc($force = false)
 	{
 		if ($force || mt_rand(0, 1000000) < $this->gcProbability) {
-			$query = new Query;
-			$query->delete($this->cacheTableName, 'expire > 0 AND expire < ' . time())
-				->createCommand($this->getDb())
-				->execute();
+			$command = $this->getDb()->createCommand();
+			$command->delete($this->cacheTableName, 'expire > 0 AND expire < ' . time())->execute();
 		}
 	}
 
@@ -249,10 +245,8 @@ class DbCache extends Cache
 	 */
 	protected function flushValues()
 	{
-		$query = new Query;
-		$query->delete($this->cacheTableName)
-			->createCommand($this->getDb())
-			->execute();
+		$command = $this->getDb()->createCommand();
+		$command->delete($this->cacheTableName)->execute();
 		return true;
 	}
 }
diff --git a/framework/caching/DbDependency.php b/framework/caching/DbDependency.php
index dcc7e37..7ffdb4e 100644
--- a/framework/caching/DbDependency.php
+++ b/framework/caching/DbDependency.php
@@ -9,7 +9,7 @@
 
 namespace yii\caching;
 
-use yii\base\Exception;
+use yii\base\InvalidConfigException;
 use yii\db\Connection;
 use yii\db\Query;
 
@@ -68,6 +68,9 @@ class DbDependency extends Dependency
 	protected function generateDependencyData()
 	{
 		$db = $this->getDb();
+		/**
+		 * @var \yii\db\Command $command
+		 */
 		$command = $this->query->createCommand($db);
 		if ($db->enableQueryCache) {
 			// temporarily disable and re-enable query caching
@@ -83,7 +86,7 @@ class DbDependency extends Dependency
 	/**
 	 * Returns the DB connection instance used for caching purpose.
 	 * @return Connection the DB connection instance
-	 * @throws Exception if [[connectionID]] does not point to a valid application component.
+	 * @throws InvalidConfigException if [[connectionID]] does not point to a valid application component.
 	 */
 	public function getDb()
 	{
@@ -92,7 +95,7 @@ class DbDependency extends Dependency
 			if ($db instanceof Connection) {
 				$this->_db = $db;
 			} else {
-				throw new Exception("DbDependency.connectionID must refer to the ID of a DB connection application component.");
+				throw new InvalidConfigException("DbCache::connectionID must refer to the ID of a DB application component.");
 			}
 		}
 		return $this->_db;
diff --git a/framework/caching/FileCache.php b/framework/caching/FileCache.php
index 330ef86..f97861f 100644
--- a/framework/caching/FileCache.php
+++ b/framework/caching/FileCache.php
@@ -9,7 +9,7 @@
 
 namespace yii\caching;
 
-use yii\base\Exception;
+use yii\base\InvalidConfigException;
 
 /**
  * FileCache implements a cache component using files.
@@ -42,10 +42,10 @@ class FileCache extends Cache
 	public $directoryLevel = 1;
 	/**
 	 * @var integer the probability (parts per million) that garbage collection (GC) should be performed
-	 * when storing a piece of data in the cache. Defaults to 100, meaning 0.01% chance.
-	 * This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.
+	 * when storing a piece of data in the cache. Defaults to 10, meaning 0.001% chance.
+	 * This number should be between 0 and 1000000. A value 0 means no GC will be performed at all.
 	 **/
-	public $gcProbability = 100;
+	public $gcProbability = 10;
 
 	/**
 	 * Initializes this component by ensuring the existence of the cache path.
@@ -55,7 +55,7 @@ class FileCache extends Cache
 		parent::init();
 		$this->cachePath = \Yii::getAlias($this->cachePath);
 		if ($this->cachePath === false) {
-			throw new Exception('FileCache.cachePath must be a valid path alias.');
+			throw new InvalidConfigException('FileCache.cachePath must be a valid path alias.');
 		}
 		if (!is_dir($this->cachePath)) {
 			mkdir($this->cachePath, 0777, true);
diff --git a/framework/caching/MemCache.php b/framework/caching/MemCache.php
index 1c153d9..288c3ee 100644
--- a/framework/caching/MemCache.php
+++ b/framework/caching/MemCache.php
@@ -10,6 +10,7 @@
 namespace yii\caching;
 
 use yii\base\Exception;
+use yii\base\InvalidConfigException;
 
 /**
  * MemCache implements a cache application component based on [memcache](http://pecl.php.net/package/memcache)
@@ -109,12 +110,12 @@ class MemCache extends Cache
 	 * @return \Memcache|\Memcached the memcache (or memcached) object used by this cache component.
 	 * @throws Exception if memcache or memcached extension is not loaded
 	 */
-	public function getMemCache()
+	public function getMemcache()
 	{
 		if ($this->_cache === null) {
 			$extension = $this->useMemcached ? 'memcached' : 'memcache';
 			if (!extension_loaded($extension)) {
-				throw new Exception("MemCache requires PHP $extension extension to be loaded.");
+				throw new InvalidConfigException("MemCache requires PHP $extension extension to be loaded.");
 			}
 			$this->_cache = $this->useMemcached ? new \Memcached : new \Memcache;
 		}
diff --git a/framework/caching/ZendDataCache.php b/framework/caching/ZendDataCache.php
index b9941e5..8716a36 100644
--- a/framework/caching/ZendDataCache.php
+++ b/framework/caching/ZendDataCache.php
@@ -31,7 +31,7 @@ class ZendDataCache extends Cache
 	protected function getValue($key)
 	{
 		$result = zend_shm_cache_fetch($key);
-		return $result !== NULL ? $result : false;
+		return $result === null ? false : $result;
 	}
 
 	/**