diff --git a/lib/private/server.php b/lib/private/server.php
index 7fa06298b2..ff34cfdccb 100644
--- a/lib/private/server.php
+++ b/lib/private/server.php
@@ -14,6 +14,7 @@ use OC\Security\Crypto;
 use OC\Security\SecureRandom;
 use OCP\IServerContainer;
 use OCP\ISession;
+use OC\Tagging\TagMapper;
 
 /**
  * Class Server
@@ -68,9 +69,13 @@ class Server extends SimpleContainer implements IServerContainer {
 		$this->registerService('PreviewManager', function ($c) {
 			return new PreviewManager();
 		});
+		$this->registerService('TagMapper', function($c) {
+			return new TagMapper($c->getDb());
+		});
 		$this->registerService('TagManager', function ($c) {
+			$tagMapper = $c->query('TagMapper');
 			$user = \OC_User::getUser();
-			return new TagManager($user);
+			return new TagManager($tagMapper, $user);
 		});
 		$this->registerService('RootFolder', function ($c) {
 			// TODO: get user and user manager from container as well
diff --git a/lib/private/share/share.php b/lib/private/share/share.php
index 5314e09b8d..b827b84a9b 100644
--- a/lib/private/share/share.php
+++ b/lib/private/share/share.php
@@ -1181,7 +1181,7 @@ class Share extends \OC\Share\Constants {
 			}
 		}
 		// TODO Add option for collections to be collection of themselves, only 'folder' does it now...
-		if (!self::getBackend($itemType) instanceof \OCP\Share_Backend_Collection || $itemType != 'folder') {
+		if (isset(self::$backendTypes[$itemType]) && (!self::getBackend($itemType) instanceof \OCP\Share_Backend_Collection || $itemType != 'folder')) {
 			unset($collectionTypes[0]);
 		}
 		// Return array if collections were found or the item type is a
@@ -1192,6 +1192,57 @@ class Share extends \OC\Share\Constants {
 		return false;
 	}
 
+	/**
+	* Get the owners of items shared with a user.
+	*
+	* @param string $user The user the items are shared with.
+	* @param string $type The type of the items shared with the user.
+	* @param boolean $includeCollections Include collection item types (optional)
+	* @param boolean $includeOwner include owner in the list of users the item is shared with (optional)
+	* @return array
+	*/
+	public static function getSharedItemsOwners($user, $type, $includeCollections = false, $includeOwner = false) {
+		// First, we find out if $type is part of a collection (and if that collection is part of
+		// another one and so on).
+		$collectionTypes = array();
+		if (!$includeCollections || !$collectionTypes = self::getCollectionItemTypes($type)) {
+			$collectionTypes[] = $type;
+		}
+
+		// Of these collection types, along with our original $type, we make a
+		// list of the ones for which a sharing backend has been registered.
+		// FIXME: Ideally, we wouldn't need to nest getItemsSharedWith in this loop but just call it
+		// with its $includeCollections parameter set to true. Unfortunately, this fails currently.
+		$allMaybeSharedItems = array();
+		foreach ($collectionTypes as $collectionType) {
+			if (isset(self::$backends[$collectionType])) {
+				$allMaybeSharedItems[$collectionType] = self::getItemsSharedWithUser(
+					$collectionType,
+					$user,
+					self::FORMAT_NONE
+				);
+			}
+		}
+
+		$owners = array();
+		if ($includeOwner) {
+			$owners[] = $user;
+		}
+
+		// We take a look at all shared items of the given $type (or of the collections it is part of)
+		// and find out their owners. Then, we gather the tags for the original $type from all owners,
+		// and return them as elements of a list that look like "Tag (owner)".
+		foreach ($allMaybeSharedItems as $collectionType => $maybeSharedItems) {
+			foreach ($maybeSharedItems as $sharedItem) {
+				if (isset($sharedItem['id'])) { //workaround for https://github.com/owncloud/core/issues/2814
+					$owners[] = $sharedItem['uid_owner'];
+				}
+			}
+		}
+
+		return $owners;
+	}
+
 	/**
 	 * Get shared items from the database
 	 * @param string $itemType
diff --git a/lib/private/tagging/tag.php b/lib/private/tagging/tag.php
new file mode 100644
index 0000000000..3ea9fbac20
--- /dev/null
+++ b/lib/private/tagging/tag.php
@@ -0,0 +1,89 @@
+<?php
+/**
+* ownCloud - Tag class
+*
+* @author Bernhard Reiter
+* @copyright 2014 Bernhard Reiter <ockham@raz.or.at>
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
+* License as published by the Free Software Foundation; either
+* version 3 of the License, or any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU AFFERO GENERAL PUBLIC LICENSE for more details.
+*
+* You should have received a copy of the GNU Affero General Public
+* License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+*
+*/
+
+namespace OC\Tagging;
+
+use \OCP\AppFramework\Db\Entity;
+
+/**
+ * Class to represent a tag.
+ *
+ * @method string getOwner()
+ * @method void setOwner(string $owner)
+ * @method string getType()
+ * @method void setType(string $type)
+ * @method string getName()
+ * @method void setName(string $name)
+ */
+class Tag extends Entity {
+
+	protected $owner;
+	protected $type;
+	protected $name;
+
+	/**
+	* Constructor.
+	*
+	* @param string $owner The tag's owner
+	* @param string $type The type of item this tag is used for
+	* @param string $name The tag's name
+	*/
+	public function __construct($owner = null, $type = null, $name = null) {
+		$this->setOwner($owner);
+		$this->setType($type);
+		$this->setName($name);
+	}
+
+	/**
+	 * Transform a database columnname to a property
+	 *
+	 * @param string $columnName the name of the column
+	 * @return string the property name
+	 * @todo migrate existing database columns to the correct names
+	 * to be able to drop this direct mapping
+	 */
+	public function columnToProperty($columnName){
+		if ($columnName === 'category') {
+		    return 'name';
+		} elseif ($columnName === 'uid') {
+		    return 'owner';
+		} else {
+		    return parent::columnToProperty($columnName);
+		}
+	}
+
+	/**
+	 * Transform a property to a database column name
+	 *
+	 * @param string $property the name of the property
+	 * @return string the column name
+	 */
+	public function propertyToColumn($property){
+		if ($property === 'name') {
+		    return 'category';
+		} elseif ($property === 'owner') {
+		    return 'uid';
+		} else {
+		    return parent::propertyToColumn($property);
+		}
+	}
+}
diff --git a/lib/private/tagging/tagmapper.php b/lib/private/tagging/tagmapper.php
new file mode 100644
index 0000000000..6c9bec7aa5
--- /dev/null
+++ b/lib/private/tagging/tagmapper.php
@@ -0,0 +1,77 @@
+<?php
+/**
+* ownCloud - TagMapper class
+*
+* @author Bernhard Reiter
+* @copyright 2014 Bernhard Reiter <ockham@raz.or.at>
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
+* License as published by the Free Software Foundation; either
+* version 3 of the License, or any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU AFFERO GENERAL PUBLIC LICENSE for more details.
+*
+* You should have received a copy of the GNU Affero General Public
+* License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+*
+*/
+
+namespace OC\Tagging;
+
+use \OCP\AppFramework\Db\Mapper,
+    \OCP\AppFramework\Db\DoesNotExistException,
+    \OCP\IDb;
+
+/**
+ * Mapper for Tag entity
+ */
+class TagMapper extends Mapper {
+
+	/**
+	* Constructor.
+	*
+	* @param IDb $db Instance of the Db abstraction layer.
+	*/
+	public function __construct(IDb $db) {
+		parent::__construct($db, 'vcategory', 'OC\Tagging\Tag');
+	}
+
+	/**
+	* Load tags from the database.
+	*
+	* @param array|string $owners The user(s) whose tags we are going to load.
+	* @param string $type The type of item for which we are loading tags.
+	* @return array An array of Tag objects.
+	*/
+	public function loadTags($owners, $type) {
+		if(!is_array($owners)) {
+			$owners = array($owners);
+		}
+
+		$sql = 'SELECT `id`, `uid`, `type`, `category` FROM `' . $this->getTableName() . '` '
+			. 'WHERE `uid` IN (' . str_repeat('?,', count($owners)-1) . '?) AND `type` = ? ORDER BY `category`';
+		return $this->findEntities($sql, array_merge($owners, array($type)));
+	}
+
+	/**
+	* Check if a given Tag object already exists in the database.
+	*
+	* @param Tag $tag The tag to look for in the database.
+	* @return bool
+	*/
+	public function tagExists($tag) {
+		$sql = 'SELECT `id`, `uid`, `type`, `category` FROM `' . $this->getTableName() . '` '
+			. 'WHERE `uid` = ? AND `type` = ? AND `category` = ?';
+		try {
+			$this->findEntity($sql, array($tag->getOwner(), $tag->getType(), $tag->getName()));
+		} catch (DoesNotExistException $e) {
+			return false;
+		}
+		return true;
+	}
+}
+
diff --git a/lib/private/tagmanager.php b/lib/private/tagmanager.php
index 9a371a1125..d5bff04acf 100644
--- a/lib/private/tagmanager.php
+++ b/lib/private/tagmanager.php
@@ -33,6 +33,8 @@
 
 namespace OC;
 
+use OC\Tagging\TagMapper;
+
 class TagManager implements \OCP\ITagManager {
 
 	/**
@@ -40,15 +42,24 @@ class TagManager implements \OCP\ITagManager {
 	 *
 	 * @var string
 	 */
-	private $user = null;
+	private $user;
+
+	/**
+	 * TagMapper
+	 *
+	 * @var TagMapper
+	 */
+	private $mapper;
 
 	/**
 	* Constructor.
 	*
-	* @param string $user The user whos data the object will operate on.
+	* @param TagMapper $mapper Instance of the TagMapper abstraction layer.
+	* @param string $user The user whose data the object will operate on.
 	*/
-	public function __construct($user) {
+	public function __construct(TagMapper $mapper, $user) {
 
+		$this->mapper = $mapper;
 		$this->user = $user;
 
 	}
@@ -59,10 +70,11 @@ class TagManager implements \OCP\ITagManager {
 	* @see \OCP\ITags
 	* @param string $type The type identifier e.g. 'contact' or 'event'.
 	* @param array $defaultTags An array of default tags to be used if none are stored.
+	* @param boolean $includeShared Whether to include tags for items shared with this user by others.
 	* @return \OCP\ITags
 	*/
-	public function load($type, $defaultTags=array()) {
-		return new Tags($this->user, $type, $defaultTags);
+	public function load($type, $defaultTags=array(), $includeShared=false) {
+		return new Tags($this->mapper, $this->user, $type, $defaultTags, $includeShared);
 	}
 
-}
\ No newline at end of file
+}
diff --git a/lib/private/tags.php b/lib/private/tags.php
index 0e58789ecd..bab3d49528 100644
--- a/lib/private/tags.php
+++ b/lib/private/tags.php
@@ -34,6 +34,9 @@
 
 namespace OC;
 
+use \OC\Tagging\Tag,
+    \OC\Tagging\TagMapper;
+
 class Tags implements \OCP\ITags {
 
 	/**
@@ -55,14 +58,44 @@ class Tags implements \OCP\ITags {
 	 *
 	 * @var string
 	 */
-	private $type = null;
+	private $type;
 
 	/**
 	 * User
 	 *
 	 * @var string
 	 */
-	private $user = null;
+	private $user;
+
+	/**
+	 * Are we including tags for shared items?
+	 *
+	 * @var bool
+	 */
+	private $includeShared = false;
+
+	/**
+	 * The current user, plus any owners of the items shared with the current
+	 * user, if $this->includeShared === true.
+	 *
+	 * @var array
+	 */
+	private $owners = array();
+
+	/**
+	 * The Mapper we're using to communicate our Tag objects to the database.
+	 *
+	 * @var TagMapper
+	 */
+	private $mapper;
+
+	/**
+	 * The sharing backend for objects of $this->type. Required if
+	 * $this->includeShared === true to determine ownership of items.
+	 *
+	 * @var \OCP\Share_Backend
+	 */
+	private $backend;
 
 	const TAG_TABLE = '*PREFIX*vcategory';
 	const RELATION_TABLE = '*PREFIX*vcategory_to_object';
@@ -72,47 +105,29 @@ class Tags implements \OCP\ITags {
 	/**
 	* Constructor.
 	*
-	* @param string $user The user whos data the object will operate on.
-	* @param string $type
+	* @param TagMapper $mapper Instance of the TagMapper abstraction layer.
+	* @param string $user The user whose data the object will operate on.
+	* @param string $type The type of items for which tags will be loaded.
+	* @param array $defaultTags Tags that should be created at construction.
+	* @param boolean $includeShared Whether to include tags for items shared with this user by others.
 	*/
-	public function __construct($user, $type, $defaultTags = array()) {
+	public function __construct(TagMapper $mapper, $user, $type, $defaultTags = array(), $includeShared = false) {
+		$this->mapper = $mapper;
 		$this->user = $user;
 		$this->type = $type;
-		$this->loadTags($defaultTags);
-	}
-
-	/**
-	* Load tags from db.
-	*
-	*/
-	protected function loadTags($defaultTags=array()) {
-		$this->tags = array();
-		$result = null;
-		$sql = 'SELECT `id`, `category` FROM `' . self::TAG_TABLE . '` '
-			. 'WHERE `uid` = ? AND `type` = ? ORDER BY `category`';
-		try {
-			$stmt = \OCP\DB::prepare($sql);
-			$result = $stmt->execute(array($this->user, $this->type));
-			if (\OCP\DB::isError($result)) {
-				\OCP\Util::writeLog('core', __METHOD__. ', DB error: ' . \OCP\DB::getErrorMessage($result), \OCP\Util::ERROR);
-			}
-		} catch(\Exception $e) {
-			\OCP\Util::writeLog('core', __METHOD__.', exception: '.$e->getMessage(),
-				\OCP\Util::ERROR);
-		}
-
-		if(!is_null($result)) {
-			while( $row = $result->fetchRow()) {
-				$this->tags[$row['id']] = $row['category'];
-			}
+		$this->includeShared = $includeShared;
+		$this->owners = array($this->user);
+		if ($this->includeShared) {
+			$this->owners = array_merge($this->owners, \OC\Share\Share::getSharedItemsOwners($this->user, $this->type, true));
+			$this->backend = \OC\Share\Share::getBackend($this->type);
 		}
+		$this->tags = $this->mapper->loadTags($this->owners, $this->type);
 
 		if(count($defaultTags) > 0 && count($this->tags) === 0) {
 			$this->addMultiple($defaultTags, true);
 		}
 		\OCP\Util::writeLog('core', __METHOD__.', tags: ' . print_r($this->tags, true),
 			\OCP\Util::DEBUG);
-
 	}
 
 	/**
@@ -124,13 +139,28 @@ class Tags implements \OCP\ITags {
 		return count($this->tags) === 0;
 	}
 
+	/**
+	* Returns an array mapping a given tag's properties to its values:
+	* ['id' => 0, 'name' = 'Tag', 'owner' = 'User', 'type' => 'tagtype']
+	*
+	* @param string $id The ID of the tag that is going to be mapped
+	* @return array|false
+	*/
+	public function getTag($id) {
+		$key = $this->getTagById($id);
+		if ($key !== false) {
+			return $this->tagMap($this->tags[$key]);
+		}
+		return false;
+	}
+
 	/**
 	* Get the tags for a specific user.
 	*
-	* This returns an array with id/name maps:
+	* This returns an array with maps containing each tag's properties:
 	* [
-	* 	['id' => 0, 'name' = 'First tag'],
-	* 	['id' => 1, 'name' = 'Second tag'],
+	* 	['id' => 0, 'name' = 'First tag', 'owner' = 'User', 'type' => 'tagtype'],
+	* 	['id' => 1, 'name' = 'Shared tag', 'owner' = 'Other user', 'type' => 'tagtype'],
 	* ]
 	*
 	* @return array
@@ -140,22 +170,35 @@ class Tags implements \OCP\ITags {
 			return array();
 		}
 
-		$tags = array_values($this->tags);
-		uasort($tags, 'strnatcasecmp');
+		usort($this->tags, function($a, $b) {
+			return strnatcasecmp($a->getName(), $b->getName());
+		});
 		$tagMap = array();
 
-		foreach($tags as $tag) {
-			if($tag !== self::TAG_FAVORITE) {
-				$tagMap[] = array(
-					'id' => $this->array_searchi($tag, $this->tags),
-					'name' => $tag
-					);
+		foreach($this->tags as $tag) {
+			if($tag->getName() !== self::TAG_FAVORITE) {
+				$tagMap[] = $this->tagMap($tag);
 			}
 		}
 		return $tagMap;
 
 	}
 
+	/**
+	* Return only the tags owned by the given user, omitting any tags shared
+	* by other users.
+	*
+	* @param string $user The user whose tags are to be checked.
+	* @return array An array of Tag objects.
+	*/
+	public function getTagsForUser($user) {
+		return array_filter($this->tags,
+			function($tag) use($user) {
+				return $tag->getOwner() === $user;
+			}
+		);
+	}
+
 	/**
 	* Get the a list if items tagged with $tag.
 	*
@@ -174,7 +217,7 @@ class Tags implements \OCP\ITags {
 				\OCP\Util::writeLog('core', __METHOD__.', Cannot use empty tag names', \OCP\Util::DEBUG);
 				return false;
 			}
-			$tagId = $this->array_searchi($tag, $this->tags);
+			$tagId = $this->getTagId($tag);
 		}
 
 		if($tagId === false) {
@@ -203,7 +246,22 @@ class Tags implements \OCP\ITags {
 
 		if(!is_null($result)) {
 			while( $row = $result->fetchRow()) {
-				$ids[] = (int)$row['objid'];
+				$id = (int)$row['objid'];
+
+				if ($this->includeShared) {
+					// We have to check if we are really allowed to access the
+					// items that are tagged with $tag. To that end, we ask the
+					// corresponding sharing backend if the item identified by $id
+					// is owned by any of $this->owners.
+					foreach ($this->owners as $owner) {
+						if ($this->backend->isValidSource($id, $owner)) {
+							$ids[] = $id;
+							break;
+						}
+					}
+				} else {
+					$ids[] = $id;
+				}
 			}
 		}
 
@@ -211,13 +269,26 @@ class Tags implements \OCP\ITags {
 	}
 
 	/**
-	* Checks whether a tag is already saved.
+	* Checks whether a tag is saved for the given user,
+	* disregarding the ones shared with him or her.
 	*
-	* @param string $name The name to check for.
+	* @param string $name The tag name to check for.
+	* @param string $user The user whose tags are to be checked.
+	* @return bool
+	*/
+	public function userHasTag($name, $user) {
+		$key = $this->array_searchi($name, $this->getTagsForUser($user));
+		return ($key !== false) ? $this->tags[$key]->getId() : false;
+	}
+
+	/**
+	* Checks whether a tag is saved for or shared with the current user.
+	*
+	* @param string $name The tag name to check for.
 	* @return bool
 	*/
 	public function hasTag($name) {
-		return $this->in_arrayi($name, $this->tags);
+		return $this->getTagId($name) !== false;
 	}
 
 	/**
@@ -233,41 +304,27 @@ class Tags implements \OCP\ITags {
 			\OCP\Util::writeLog('core', __METHOD__.', Cannot add an empty tag', \OCP\Util::DEBUG);
 			return false;
 		}
-		if($this->hasTag($name)) {
+		if($this->userHasTag($name, $this->user)) {
 			\OCP\Util::writeLog('core', __METHOD__.', name: ' . $name. ' exists already', \OCP\Util::DEBUG);
 			return false;
 		}
 		try {
-			$result = \OCP\DB::insertIfNotExist(
-				self::TAG_TABLE,
-				array(
-					'uid' => $this->user,
-					'type' => $this->type,
-					'category' => $name,
-				)
-			);
-			if (\OCP\DB::isError($result)) {
-				\OCP\Util::writeLog('core', __METHOD__. 'DB error: ' . \OCP\DB::getErrorMessage($result), \OCP\Util::ERROR);
-				return false;
-			} elseif((int)$result === 0) {
-				\OCP\Util::writeLog('core', __METHOD__.', Tag already exists: ' . $name, \OCP\Util::DEBUG);
-				return false;
-			}
+			$tag = new Tag($this->user, $this->type, $name);
+			$tag = $this->mapper->insert($tag);
+			$this->tags[] = $tag;
 		} catch(\Exception $e) {
 			\OCP\Util::writeLog('core', __METHOD__.', exception: '.$e->getMessage(),
 				\OCP\Util::ERROR);
 			return false;
 		}
-		$id = \OCP\DB::insertid(self::TAG_TABLE);
-		\OCP\Util::writeLog('core', __METHOD__.', id: ' . $id, \OCP\Util::DEBUG);
-		$this->tags[$id] = $name;
-		return $id;
+		\OCP\Util::writeLog('core', __METHOD__.', id: ' . $tag->getId(), \OCP\Util::DEBUG);
+		return $tag->getId();
 	}
 
 	/**
 	* Rename tag.
 	*
-	* @param string $from The name of the existing tag
+	* @param string|integer $from The name or ID of the existing tag
 	* @param string $to The new name of the tag.
 	* @return bool
 	*/
@@ -280,27 +337,30 @@ class Tags implements \OCP\ITags {
 			return false;
 		}
 
-		$id = $this->array_searchi($from, $this->tags);
-		if($id === false) {
+		if (is_numeric($from)) {
+			$key = $this->getTagById($from);
+		} else {
+			$key = $this->getTagByName($from);
+		}
+		if($key === false) {
 			\OCP\Util::writeLog('core', __METHOD__.', tag: ' . $from. ' does not exist', \OCP\Util::DEBUG);
 			return false;
 		}
+		$tag = $this->tags[$key];
+
+		if($this->userHasTag($to, $tag->getOwner())) {
+			\OCP\Util::writeLog('core', __METHOD__.', A tag named ' . $to. ' already exists for user ' . $tag->getOwner() . '.', \OCP\Util::DEBUG);
+			return false;
+		}
 
-		$sql = 'UPDATE `' . self::TAG_TABLE . '` SET `category` = ? '
-			. 'WHERE `uid` = ? AND `type` = ? AND `id` = ?';
 		try {
-			$stmt = \OCP\DB::prepare($sql);
-			$result = $stmt->execute(array($to, $this->user, $this->type, $id));
-			if (\OCP\DB::isError($result)) {
-				\OCP\Util::writeLog('core', __METHOD__. 'DB error: ' . \OCP\DB::getErrorMessage($result), \OCP\Util::ERROR);
-				return false;
-			}
+			$tag->setName($to);
+			$this->tags[$key] = $this->mapper->update($tag);
 		} catch(\Exception $e) {
 			\OCP\Util::writeLog('core', __METHOD__.', exception: '.$e->getMessage(),
 				\OCP\Util::ERROR);
 			return false;
 		}
-		$this->tags[$id] = $to;
 		return true;
 	}
 
@@ -308,7 +368,7 @@ class Tags implements \OCP\ITags {
 	* Add a list of new tags.
 	*
 	* @param string[] $names A string with a name or an array of strings containing
-	* the name(s) of the to add.
+	* the name(s) of the tag(s) to add.
 	* @param bool $sync When true, save the tags
 	* @param int|null $id int Optional object id to add to this|these tag(s)
 	* @return bool Returns false on error.
@@ -322,9 +382,8 @@ class Tags implements \OCP\ITags {
 
 		$newones = array();
 		foreach($names as $name) {
-			if(($this->in_arrayi(
-				$name, $this->tags) == false) && $name !== '') {
-				$newones[] = $name;
+			if(!$this->hasTag($name) && $name !== '') {
+				$newones[] = new Tag($this->user, $this->type, $name);
 			}
 			if(!is_null($id) ) {
 				// Insert $objectid, $categoryid  pairs if not exist.
@@ -346,26 +405,26 @@ class Tags implements \OCP\ITags {
 		if(is_array($this->tags)) {
 			foreach($this->tags as $tag) {
 				try {
-					\OCP\DB::insertIfNotExist(self::TAG_TABLE,
-						array(
-							'uid' => $this->user,
-							'type' => $this->type,
-							'category' => $tag,
-						));
+					if (!$this->mapper->tagExists($tag)) {
+						$this->mapper->insert($tag);
+					}
 				} catch(\Exception $e) {
 					\OCP\Util::writeLog('core', __METHOD__.', exception: '.$e->getMessage(),
 						\OCP\Util::ERROR);
 				}
 			}
+
 			// reload tags to get the proper ids.
-			$this->loadTags();
+			$this->tags = $this->mapper->loadTags($this->owners, $this->type);
+			\OCP\Util::writeLog('core', __METHOD__.', tags: ' . print_r($this->tags, true),
+				\OCP\Util::DEBUG);
 			// Loop through temporarily cached objectid/tagname pairs
 			// and save relations.
 			$tags = $this->tags;
 			// For some reason this is needed or array_search(i) will return 0..?
 			ksort($tags);
 			foreach(self::$relations as $relation) {
-				$tagId = $this->array_searchi($relation['tag'], $tags);
+				$tagId = $this->getTagId($relation['tag']);
 				\OCP\Util::writeLog('core', __METHOD__ . 'catid, ' . $relation['tag'] . ' ' . $tagId, \OCP\Util::DEBUG);
 				if($tagId) {
 					try {
@@ -493,7 +552,7 @@ class Tags implements \OCP\ITags {
 	* @return boolean
 	*/
 	public function addToFavorites($objid) {
-		if(!$this->hasTag(self::TAG_FAVORITE)) {
+		if(!$this->userHasTag(self::TAG_FAVORITE, $this->user)) {
 			$this->add(self::TAG_FAVORITE);
 		}
 		return $this->tagAs($objid, self::TAG_FAVORITE);
@@ -526,7 +585,7 @@ class Tags implements \OCP\ITags {
 			if(!$this->hasTag($tag)) {
 				$this->add($tag);
 			}
-			$tagId =  $this->array_searchi($tag, $this->tags);
+			$tagId =  $this->getTagId($tag);
 		} else {
 			$tagId = $tag;
 		}
@@ -559,7 +618,7 @@ class Tags implements \OCP\ITags {
 				\OCP\Util::writeLog('core', __METHOD__.', Tag name is empty', \OCP\Util::DEBUG);
 				return false;
 			}
-			$tagId =  $this->array_searchi($tag, $this->tags);
+			$tagId =  $this->getTagId($tag);
 		} else {
 			$tagId = $tag;
 		}
@@ -578,9 +637,9 @@ class Tags implements \OCP\ITags {
 	}
 
 	/**
-	* Delete tags from the
+	* Delete tags from the database.
 	*
-	* @param string[] $names An array of tags to delete
+	* @param string[]|integer[] $names An array of tags (names or IDs) to delete
 	* @return bool Returns false on error
 	*/
 	public function delete($names) {
@@ -596,21 +655,19 @@ class Tags implements \OCP\ITags {
 		foreach($names as $name) {
 			$id = null;
 
-			if($this->hasTag($name)) {
-				$id = $this->array_searchi($name, $this->tags);
-				unset($this->tags[$id]);
+			if (is_numeric($name)) {
+				$key = $this->getTagById($name);
+			} else {
+				$key = $this->getTagByName($name);
 			}
-			try {
-				$stmt = \OCP\DB::prepare('DELETE FROM `' . self::TAG_TABLE . '` WHERE '
-					. '`uid` = ? AND `type` = ? AND `category` = ?');
-				$result = $stmt->execute(array($this->user, $this->type, $name));
-				if (\OCP\DB::isError($result)) {
-					\OCP\Util::writeLog('core', __METHOD__. 'DB error: ' . \OCP\DB::getErrorMessage($result), \OCP\Util::ERROR);
-				}
-			} catch(\Exception $e) {
-				\OCP\Util::writeLog('core', __METHOD__ . ', exception: '
-					. $e->getMessage(), \OCP\Util::ERROR);
-				return false;
+			if ($key !== false) {
+				$tag = $this->tags[$key];
+				$id = $tag->getId();
+				unset($this->tags[$key]);
+				$this->mapper->delete($tag);
+			} else {
+				\OCP\Util::writeLog('core', __METHOD__ . 'Cannot delete tag ' . $name
+					. ': not found.', \OCP\Util::ERROR);
 			}
 			if(!is_null($id) && $id !== false) {
 				try {
@@ -634,19 +691,67 @@ class Tags implements \OCP\ITags {
 		return true;
 	}
 
-	// case-insensitive in_array
-	private function in_arrayi($needle, $haystack) {
+	// case-insensitive array_search
+	protected function array_searchi($needle, $haystack, $mem='getName') {
 		if(!is_array($haystack)) {
 			return false;
 		}
-		return in_array(strtolower($needle), array_map('strtolower', $haystack));
+		return array_search(strtolower($needle), array_map(
+			function($tag) use($mem) {
+				return strtolower(call_user_func(array($tag, $mem)));
+			}, $haystack)
+		);
 	}
 
-	// case-insensitive array_search
-	private function array_searchi($needle, $haystack) {
-		if(!is_array($haystack)) {
-			return false;
+	/**
+	* Get a tag's ID.
+	*
+	* @param string $name The tag name to look for.
+	* @return string|bool The tag's id or false if no matching tag is found.
+	*/
+	private function getTagId($name) {
+		$key = $this->array_searchi($name, $this->tags);
+		if ($key !== false) {
+			return $this->tags[$key]->getId();
 		}
-		return array_search(strtolower($needle), array_map('strtolower', $haystack));
+		return false;
+	}
+
+	/**
+	* Get a tag by its name.
+	*
+	* @param string $name The tag name.
+	* @return integer|bool The tag object's offset within the $this->tags
+	*                      array or false if it doesn't exist.
+	*/
+	private function getTagByName($name) {
+		return $this->array_searchi($name, $this->tags, 'getName');
+	}
+
+	/**
+	* Get a tag by its ID.
+	*
+	* @param string $id The tag ID to look for.
+	* @return integer|bool The tag object's offset within the $this->tags
+	*                      array or false if it doesn't exist.
+	*/
+	private function getTagById($id) {
+		return $this->array_searchi($id, $this->tags, 'getId');
+	}
+
+	/**
+	* Returns an array mapping a given tag's properties to its values:
+	* ['id' => 0, 'name' = 'Tag', 'owner' = 'User', 'type' => 'tagtype']
+	*
+	* @param Tag $tag The tag that is going to be mapped
+	* @return array
+	*/
+	private function tagMap(Tag $tag) {
+		return array(
+			'id'    => $tag->getId(),
+			'name'  => $tag->getName(),
+			'owner' => $tag->getOwner(),
+			'type'  => $tag->getType()
+		);
 	}
 }
diff --git a/lib/public/itagmanager.php b/lib/public/itagmanager.php
index 40487de42b..54daa5cc1c 100644
--- a/lib/public/itagmanager.php
+++ b/lib/public/itagmanager.php
@@ -48,8 +48,9 @@ interface ITagManager {
 	* @see \OCP\ITags
 	* @param string $type The type identifier e.g. 'contact' or 'event'.
 	* @param array $defaultTags An array of default tags to be used if none are stored.
+	* @param boolean $includeShared Whether to include tags for items shared with this user by others.
 	* @return \OCP\ITags
 	*/
-	public function load($type, $defaultTags=array());
+	public function load($type, $defaultTags=array(), $includeShared=false);
 
-}
\ No newline at end of file
+}
diff --git a/lib/public/itags.php b/lib/public/itags.php
index 1cba07e9b5..4514746bbe 100644
--- a/lib/public/itags.php
+++ b/lib/public/itags.php
@@ -53,6 +53,15 @@ interface ITags {
 	*/
 	public function isEmpty();
 
+	/**
+	* Returns an array mapping a given tag's properties to its values:
+	* ['id' => 0, 'name' = 'Tag', 'owner' = 'User', 'type' => 'tagtype']
+	*
+	* @param string $id The ID of the tag that is going to be mapped
+	* @return array|false
+	*/
+	public function getTag($id);
+
 	/**
 	* Get the tags for a specific user.
 	*
@@ -84,6 +93,16 @@ interface ITags {
 	*/
 	public function hasTag($name);
 
+	/**
+	* Checks whether a tag is saved for the given user,
+	* disregarding the ones shared with him or her.
+	*
+	* @param string $name The tag name to check for.
+	* @param string $user The user whose tags are to be checked.
+	* @return bool
+	*/
+	public function userHasTag($name, $user);
+
 	/**
 	* Add a new tag.
 	*
@@ -95,7 +114,7 @@ interface ITags {
 	/**
 	* Rename tag.
 	*
-	* @param string $from The name of the existing tag
+	* @param string|integer $from The name or ID of the existing tag
 	* @param string $to The new name of the tag.
 	* @return bool
 	*/
@@ -162,11 +181,11 @@ interface ITags {
 	public function unTag($objid, $tag);
 
 	/**
-	* Delete tags from the
+	* Delete tags from the database
 	*
-	* @param string[] $names An array of tags to delete
+	* @param string[]|integer[] $names An array of tags (names or IDs) to delete
 	* @return bool Returns false on error
 	*/
 	public function delete($names);
 
-}
\ No newline at end of file
+}
diff --git a/tests/lib/share/backend.php b/tests/lib/share/backend.php
index 50ce24e07b..61b8f262a4 100644
--- a/tests/lib/share/backend.php
+++ b/tests/lib/share/backend.php
@@ -29,9 +29,10 @@ class Test_Share_Backend implements OCP\Share_Backend {
 
 	private $testItem1 = 'test.txt';
 	private $testItem2 = 'share.txt';
+	private $testId = 1;
 
 	public function isValidSource($itemSource, $uidOwner) {
-		if ($itemSource == $this->testItem1 || $itemSource == $this->testItem2) {
+		if ($itemSource == $this->testItem1 || $itemSource == $this->testItem2 || $itemSource == 1) {
 			return true;
 		}
 	}
diff --git a/tests/lib/tags.php b/tests/lib/tags.php
index 976b4b4fdc..2f7a1e817f 100644
--- a/tests/lib/tags.php
+++ b/tests/lib/tags.php
@@ -34,7 +34,8 @@ class Test_Tags extends PHPUnit_Framework_TestCase {
 		$this->objectType = uniqid('type_');
 		OC_User::createUser($this->user, 'pass');
 		OC_User::setUserId($this->user);
-		$this->tagMgr = new OC\TagManager($this->user);
+		$this->tagMapper = new OC\Tagging\TagMapper(new OC\AppFramework\Db\Db());
+		$this->tagMgr = new OC\TagManager($this->tagMapper, $this->user);
 
 	}
 
@@ -84,7 +85,36 @@ class Test_Tags extends PHPUnit_Framework_TestCase {
 			$this->assertTrue($tagger->hasTag($tag));
 		}
 
-		$this->assertCount(4, $tagger->getTags(), 'Not all tags added');
+		$tagMaps = $tagger->getTags();
+		$this->assertCount(4, $tagMaps, 'Not all tags added');
+		foreach($tagMaps as $tagMap) {
+			$this->assertEquals(null, $tagMap['id']);
+		}
+
+		// As addMultiple has been called without $sync=true, the tags aren't
+		// saved to the database, so they're gone when we reload $tagger:
+
+		$tagger = $this->tagMgr->load($this->objectType);
+		$this->assertEquals(0, count($tagger->getTags()));
+
+		// Now, we call addMultiple() with $sync=true so the tags will be
+		// be saved to the database.
+		$result = $tagger->addMultiple($tags, true);
+		$this->assertTrue((bool)$result);
+
+		$tagMaps = $tagger->getTags();
+		foreach($tagMaps as $tagMap) {
+			$this->assertNotEquals(null, $tagMap['id']);
+		}
+
+		// Reload the tagger.
+		$tagger = $this->tagMgr->load($this->objectType);
+
+		foreach($tags as $tag) {
+			$this->assertTrue($tagger->hasTag($tag));
+		}
+
+		$this->assertCount(4, $tagger->getTags(), 'Not all previously saved tags found');
 	}
 
 	public function testIsEmpty() {
@@ -120,8 +150,8 @@ class Test_Tags extends PHPUnit_Framework_TestCase {
 		$this->assertTrue($tagger->rename('Wrok', 'Work'));
 		$this->assertTrue($tagger->hasTag('Work'));
 		$this->assertFalse($tagger->hastag('Wrok'));
-		$this->assertFalse($tagger->rename('Wrok', 'Work'));
-
+		$this->assertFalse($tagger->rename('Wrok', 'Work')); // Rename non-existant tag.
+		$this->assertFalse($tagger->rename('Work', 'Family')); // Collide with existing tag.
 	}
 
 	public function testTagAs() {
@@ -160,7 +190,33 @@ class Test_Tags extends PHPUnit_Framework_TestCase {
 	public function testFavorite() {
 		$tagger = $this->tagMgr->load($this->objectType);
 		$this->assertTrue($tagger->addToFavorites(1));
+		$this->assertEquals(array(1), $tagger->getFavorites());
 		$this->assertTrue($tagger->removeFromFavorites(1));
+		$this->assertEquals(array(), $tagger->getFavorites());
+	}
+
+	public function testShareTags() {
+		$test_tag = 'TestTag';
+		OCP\Share::registerBackend('test', 'Test_Share_Backend');
+
+		$tagger = $this->tagMgr->load('test');
+		$tagger->tagAs(1, $test_tag);
+
+		$other_user = uniqid('user2_');
+		OC_User::createUser($other_user, 'pass');
+
+		OC_User::setUserId($other_user);
+		$other_tagMgr = new OC\TagManager($this->tagMapper, $other_user);
+		$other_tagger = $other_tagMgr->load('test');
+		$this->assertFalse($other_tagger->hasTag($test_tag));
+
+		OC_User::setUserId($this->user);
+		OCP\Share::shareItem('test', 1, OCP\Share::SHARE_TYPE_USER, $other_user, OCP\PERMISSION_READ);
+
+		OC_User::setUserId($other_user);
+		$other_tagger = $other_tagMgr->load('test', array(), true); // Update tags, load shared ones.
+		$this->assertTrue($other_tagger->hasTag($test_tag));
+		$this->assertContains(1, $other_tagger->getIdsForTag($test_tag));
 	}
 
 }